**4. Water quality index**

Water quality was identified based on the water quality index (WQI) [41].

$$\text{WQI} = \mathbf{100} - \sqrt{\left(\mathbf{F}\_1^2 + \mathbf{F}\_2^2 + \mathbf{F}\_3^2\right)} / \mathbf{1.73}$$

Where,

F1 **=** [Water variables that do not meet objectives/Total number of water variables]\*100 F2 **=** [Number of tests that do not meet objectives/Total number of tests]\*100 F3 = nse/0.01 nse + 0.01

### Where,

nse (normalized sum of excursions) = Σn departure/number of tests.

The variables that do not meet objectives are those parameters that exceed the WHO permissible limits. At the same time, the number of tests that do not meet objectives is the number of replicates that do not fall between permissible limits. WQI, the score was scaled between 0 to 100; higher values represent better quality of water, e.g., excellent >80, good 60–80, fair 60–40, and poor <40.


**5. Conclusion**

The study investigated green spaces in Altstetten–Albisrieden, Zürich, at two scales. At the district scale, public, community and private green spaces, categorised by their ownership and accessibility, were used to depict green space structure. The connectivity analysis of the three green-space types suggested the role of each space in the urban fabric. Four significant green space clusters and their 400-m service areas were selected as subsite cases for further investigation concerning their potential for social integration at the neighbourhood scale.

The study probed the disparities between public green spaces' structural significance and their land areas. These gaps might indicate the misfunction of some spaces and suggest that designing public green spaces entails more than merely facilitating leftover land. Providing and designing public green spaces require more careful consideration of location, size, and roles in the urban fabric. A further investigation shall also take into account public transportation networks and other transport means, which may enlarge public green spaces' service coverage and modify their connectivity at the city scale, thus generating more accurate results.

Providing more or enlarging public green spaces might encourage space use frequency and duration and, hence, improve individual health. The relation between space sizes, space-use frequency, and duration, indicated in the subsites, is not a simple linear relationship but is also impacted by other factors.

Nevertheless, the study showed that the green space structure, represented by the four subsite cases, or, more specifically, the combination of the space types, the provision of facilities and enabling various activities to be undertaken, and the setting of boundaries could impact space-use activities and its social cohesion potential. Among the subsite cases, relatively small green spaces (demonstrated in Süsslerenanlage) interwoven with private areas can benefit the community exclusively. In contrast, green spaces with clear boundaries and various functions (as in Bachwiesen) can strengthen social diversity.

The current findings naturally have some limits. The space use analysis can be improved to reflect the actual situation more accurately by obtaining more onsite observation data during different periods of the year. The demographic data of the four subsites needs to be included. This data may explain the gender or age difference and cultural structures to further our understanding of how green spaces' support for people's outdoor activities can equally cover the different social groups.

Given the challenge that Altstetten–Albisrieden needs to house another 20% population in the coming decade, the study on public green space provision and distribution will synthesise with urban densification scenarios and building typologies as the next step. Green spaces would extend and connect well to each other horizontally on the ground and vertically in building structures. Buildings and green spaces might convert their competitive relationship into collaboration. Levels of green spaces with different accessibility might encourage further community integration with various needs. Nevertheless, a careful planning and design approach involving stakeholders is necessary to optimise development and future performance.


**2. Clinical examination**

The main presenting complaints in cases of TP are often vague and non-specific; relating to milk drop, anorexia, lethargy, and weight loss [4, 10]. A review study demonstrated that in 60 animals diagnosed with fatal traumatic reticulitis (15 of which developed TP), the most common presenting sign was a sudden reduction in milk yield, which was observed in 68% of the cases.

Early signs of pericarditis, which can be detected through a clinical exam, include muffled heart sounds with associated splashing sounds, pericardial friction rubs, tachycardia, and pyrexia [10, 12]. Fluctuations in parameters such as rumen turnover, faecal output, heart rhythm, lung sounds and demeanour may also be found [12].

Pain is also an important component of TP which may present as bruxism, grunting, unwillingness to move, abducted elbows or a positive response to the cranial bar and withers test [10, 12]. Not all signs are present in every case, and they are also not exclusive to TP [12], other pathologies and physiological changes can be associated with such signs [11].

The signs mentioned above are also commonly seen in TRP cases irrespective of known TP development [7]. Clinical examinations alone have been shown to miss instances of TP. In a group of 28 animals which had TP, confirmed by necropsy, only 15 were diagnosed with TP using clinical examinations alone [13]. The lack of consistency in clinical signs between TP cattle is attributed to individuals presenting at different stages of disease with some showing evidence of HF. In addition, differences are observed as a result of the location of the foreign object, which specific anatomical structures the object has penetrated and the volume of fluid present in the pericardium [10]. Pregnancy and parturition have been also highlighted as possible contributing factors, due to increased pressure on the reticulum [13]. The variable degree of clinical signs and contributing factors associated with TP emphasises that only a tentative diagnosis can be made on clinical examination alone [4, 12, 14].

Some publications have emphasised that auscultation of the heart is the most significant aspect of a clinical exam in identifying pericarditis [3, 9]. Evidence of muffled heart sounds or other abnormal sounds such as splashing, tinkling, and rubbing are also commonly associated with pericarditis [11]. In a previous study, it was shown that muffled heart sounds had a sensitivity of 92% and specificity of 93% to pericarditis disease in 39 confirmed cases [6]. It should be noted that the presence of muffled heart sounds does not specify the type of pericarditis and the absence of such sounds does not necessarily rule out pericarditis [12]. Muffled heart sounds have also been demonstrated in other, non-cardiac diseases. One study observed muffled heart sounds in all 7 cases of pleurisy and all 5 cases of mediastinal abscesses, compared to only 39 of 55 TP cases [15]. This study also found that splashing and tinkling heart sounds were only found in the TP cattle, and not those with pleurisy or mediastinal abscesses. The presence or absence of tinkling sounds might help to rule in but not rule out TP.

Abnormal heart sounds do not always remain constant within TP cases, their presentation can change daily and the severity and time frame of disease progression of each animal should also be taken into account [16]. This highlights the need to reassess clinical signs in dubious cases. As well as auscultation, a full cardiac clinical exam should include assessment of mucous membrane colour, capillary refill time, a description of heart sound audibility and intensity with appreciation for cardiac rhythm and rate. In addition, pulse strength, rate, quality and the rhythm of both jugular and mammary veins, auscultation of lung fields and percussion of the cardiac region to assess level of cardiac dullness should be conducted [12, 17]. This comprehensive assessment allows for clarification of the clinical status of each cow and indicates whether there is potential disruption of the cardiac system. This can help indicate the most likely disease responsible, however, further diagnostic approaches are needed to fully determine the underlying aetiology and type of pericarditis, if present.

HF is the penultimate stage of all heart disease due to failure of the compensatory mechanisms [18, 19] (see **Figure 1**). Any heart disease seen in cattle can present with or without clinical signs of HF, as demonstrated in previous cases of pericarditis [19, 20]. Most clinical signs associated with chronic late stage TP relate to congestive right sided HF which can present with signs such as jugular distension, submandibular and brisket oedema [4].

It should be noted that a lack of any of the aforementioned signs of TP found on clinical examination does not mean that TP is not present. A study using clinical examination alone identified that 2 of 28 cattle under investigation had TRP with no signs of TP. However, on post mortem examination it was discovered that all 28 cases had profound signs of TP. This demonstrated that the development of TP in cases of TRP cannot be excluded via clinical assessment alone.

TP has been reported as the most common cause of pericardial disease and congestive heart failure (CHF) in cattle [15]. Despite this, other diseases should be considered when signs of congestive HF are apparent. Differentials include other causes of

#### **Table 1.**

*Commonly observed clinical signs associated with TP in order of their frequency in scientific studies.*

*Evaluation of Current and Future Diagnostic and Prognostic Techniques for Traumatic… DOI: http://dx.doi.org/10.5772/intechopen.106576*

pericarditis, bacterial endocarditis, primary dilated cardiomyopathy, congenital heart disease, cardiac lymphoma, mediastinal abscess and non-cardiac exudative pleurisy with much research evident on these other possible diseases too [10].

In conclusion, all differential diagnoses should be taken into careful consideration by the veterinarian when considering the presenting signs in suspected cases of TP. This is especially important in cases where presenting signs are vague or inconsistent. TP cannot always be ruled out by clinical examination alone and TP should always be considered when cattle present wit TRP. A full, cardiac clinical exam (**Table 1**) is paramount when reviewing the possibility of cardiac disease, to accurately provide diagnostic and prognostic information to the client.


M-F words showed better memory performance relative to F words. In the M-F trials, the M cue did not indicate whether the words were TBR or not. Hence, the participants would continue to keep the words in working memory through maintenance rehearsal until the M-R/M-F (cue 2) was presented. In contrast, in the F trials, the forgetting cues were presented immediately after the words, and then the maintenance rehearsal process was reduced or terminated. Therefore, the maintenance rehearsal interval was greater for M-F trials than for F trials. Previous studies demonstrated that the encoding of item information benefited from maintenance rehearsal (Woodward et al., 1973; Hockley et al., 2016). Therefore, in this study, the better recognition performance for M-F words than that for F words might have benefited from the greater maintenance rehearsal interval. Most important, M cues might successfully trigger a maintenance rehearsal process.

#### ERP Results

The ERP technique is most commonly used in studies of memory (see the review by Rugg and Wilding, 2000), and the P3 and LPC components are always associated with memory manipulation (Polich, 2007; Gao et al., 2016b). The ERP technique is also particularly useful in investigating the neural activity associated with cognitive control. The N2 component, which is widely generated in the medial and lateral prefrontal cortex, is always associated with the cognitive control process (see the review by Folstein and Van Petten, 2008). With the advantage of time resolution, the ERP result could reveal the time course of the neural difference between different cues.

#### Cognitive Control Process Triggered by Forgetting Cues: Frontal N2 Activity

Consistent with previous DF studies (Patrick et al., 2015; Gao et al., 2016a,b), the ERPs were more negative for the forgetting cue (i.e., M-F cue) relative to the remembering cue (i.e., M-R cue) during the 200–400 ms epoch. Specifically, the M-F cues evoked a frontal N2/P3 complex, which was absent for the M-R cues (i.e., a P3 component was evoked for M-R cues; see **Figure 3**). In addition, the F cue evoked a more negative N2 component relative to the M cue. Overall, forgetting cues were associated with enhanced N2 activity over the fronto-central scalp. This fronto-centrally distributed N2 component is usually observed on various measures of cognitive control, for example, the NoGo N2 (Bokura et al., 2001; Falkenstein, 2006) and the stop signal N2 (Kok et al., 2004). The N2 is often interpreted as reflecting cognitive control of attention, and N2 amplitudes were increased with attentional control improvement (Folstein and Van Petten, 2008; Espinet et al., 2012; Qi et al., 2017). Hourihan and Taylor (2006) argued that analogous to the process of preventing the implementation of an overt response, DF may involve a cognitive control process during overt encoding. The participants were encouraged to commit words to memory, and the forgetting instruction served to countermand this default covert action. In this study, the forgetting cues induced a similar fronto-central N2 activity as in motor stopping paradigms. This result might reflect a top-down cognitive control process in preventing TBF items from being further rehearsed.

The positive correlation between the fronto-central N2 amplitudes and the recognition accuracy revealed that enhanced fronto-central N2 activity was associated with decreased memory performance. It further confirmed the view that the N2 reflects the memory inhibition process. In this study, the forgetting cues (i.e., M-F and F cues) might trigger a more intensive cognitive control process relative to the remembering cues (i.e., M-R cues). Consequently, more amounts of cognitive resources would be allocated in further processing of M-R words relative to M-F and F words. This speculation was supported by the cue effect during the P3 time window.

#### Remembering Cue-Induced Elaborate Rehearsal Process: Parietal P3 Activity

During the P3 epoch, the mean amplitudes were increased for the remembering cues (i.e., M-R cues) relative to the forgetting cues (i.e., M-F/F cues), indicating that TBR words received a more intensive rehearsal process. The observation of a significant positive correlation between recognition accuracy and the parietal P3 amplitudes indicates that the increased P3 amplitudes might be associated with an enhanced rehearsal process. This is in line with the findings of previous DF studies, which showed that enhanced central-parietal P3 activity was positively correlated with higher subsequent memory performance (Patrick et al., 2015; Gao et al., 2016a,b). The P3 component might be a neural mark of the rehearsal process.

During the 200–400 ms time window, the M cues evoked a frontal N2 component, whereas this component was absent for the M-R cues. Instead, a P3 component was evoked (**Figure 3**). In addition, the M-R cues evoked enhanced central-parietal P3 and LPC components relative to the M cues. These results might indicate that the M cues triggered an enhanced frontal control process, and more amounts of cognitive resources were recruited for the elaborate rehearsal of M-R words. When the M cues were presented, the participants continued to keep the words in working memory through maintenance rehearsal, and these

words did not receive elaborate rehearsal until the M-R cues were presented.

#### Forgetting Process vs. Maintenance Rehearsal Process

Enhanced frontal N2 and decreased central-parietal P3 and LPC activities were also found for the M cue relative to the M-F cues, indicating that a more intensive cognitive control process might be triggered by the M cues (enhanced N2), and fewer amount of cognitive resources were recruited for further rehearsal (decreased P3 and LPC). Lee and Lee (2011) found that the memory performance was improved with increased forgetting cue duration (i.e., 1 vs. 5 s). The TBF items still received processing after the cues were presented. Consistent with this view, the enhanced P3 and LPC activities associated with the M-F cue might be due to this automatic rehearsal process, which was more intensive than the maintenance rehearsal process. Similarly, this ERP effect was also observed between the F cue and the M-F cue, indicating that M-F cues received enhanced rehearsal process.

However, because the M and F cues always preceded the M-R and M-F cues, the ERP cue effect might be modulated by this cue order. The more positive-going amplitude in the M-R/M-F condition might be due to the more negative slow waves in the baseline period (−200 to 0 ms) compared with the M condition. Maintenance of information in working memory has previously been related to negative slow waves (for a review, see Ruchkin et al., 2003; Drew et al., 2006). During the baseline time window, it is consequently possible that the ERPs are more negative for the M-R cues relative to the M cues. This potential difference in ERP amplitudes in the baseline period makes it difficult to compare the M-R and M conditions with each other, and could potentially explain the more positive-going ERPs in the M-R condition. Therefore, the ERP difference between M-F and M cues is not a good indicator to reflect the neural differences between the maintenance rehearsal and forgetting processes.

Because both the F cue and the M cue were the first cues after the words were presented, the ERP effect (F cue vs. M cue) was not influenced by the cue order effect. The F cues triggered a forgetting process and the M cues triggered a maintenance rehearsal process. Compared with the M cues, the F cues evoked a decreased fronto-central P2 component. This frontal P2 effect was also found for the F cues relative to the M-R or M-F cues. This fronto-central P2 effect reflects the enhanced selective attention process triggered by the taskrelevant stimulus (Smid et al., 1999; Bergström et al., 2007; Mecklinger et al., 2009). Some DF studies also found that remembering cues evoked an enhanced frontal P2 component than forgetting cues (Cheng et al., 2012; Gao et al., 2016a). Consistent with these findings, our study suggests that increased attentional resources might be allocated to the M cues vs. the F cues.

The F cue evoked a more negative fronto-central N2 component relative to the M cues, suggesting that the F cues triggered an enhanced control process than the M cues. In addition, the ERPs were more positive for the M cues relative to the F cues over the parietal scalp during the 200–400 ms time window. As shown in **Figure 3**, at P3 and Pz electrodes, the F cues evoked an N2 component, whereas the M cues evoked a P3 component. This might indicate that the words continued to receive a rehearsal process when the M cue was presented. However, the rehearsal process was stopped or reduced when the F cue was presented. The enhanced frontal activity might provide evidence for the attentional inhibition account, which suggests that forgetting might involve an active attentional/cognitive control process.

Some researchers found that decreased P2 and enhanced N2 components were evoked for forgetting vs. remembering cues (Gao et al., 2016a). They demonstrated that DF involves two stages. During the first stage, the attentional withdrawal process stops the TBF items from being further processed; during the second stage, the memory representations of TBF items were inhibited. Similarly, in this study, decreased P2 and enhanced N2 amplitudes were evoked for the forgetting cue (i.e., F cue) relative to the M cue. This demonstrated that the forgetting cue-induced frontal activities (P2, N2) were not modulated by the remembering cue-induced elaborate rehearsal process. It further supported the view that forgetting is an active process that involves attentional withdrawal (P2 epoch) and cognitive control (N2 epoch).

The M cues evoked reduced LPC amplitudes relative to the F cues at parietal electrodes (i.e., Pz, P4), suggesting that the TBF words received enhanced, further processing after the F cues were presented. One possibility is that it might reflect enhanced working memory maintenance and/or rehearsal process for the F condition relative to the M condition. Lee (2012) suggested that TBF words were automatically processed to the extent that cognitive resources remained available. In addition, some studies have found that the forgetting cue in an item-method DF paradigm might prompt subjects to process the TBF items (Zwissler et al., 2015; Gao et al., 2016b). Therefore, the ERP cue effect during the LPC epoch might reflect that TBF words were automatically rehearsed, and more amounts of cognitive resources were recruited for the F cues relative to the M cues. However, no significant correlation was found between the recognition performance and LPC amplitudes. An alternative explanation for this LPC effect might be that, in order to remember as many TBR words as possible, the participants might cumulatively rehearse the TBR words from preceding trials when the forgetting cue was presented (Fawcett and Taylor, 2008, 2012). This LPC activity might be associated with the study phase retrieval or cumulative rehearsal process.

Zwissler et al. (2015) suggested that frontal brain activation associated with forgetting cues might result from either non-inhibitory processes, such as attention orienting, conflict monitoring, or unsuccessful inhibition attempts. The frontal activity (i.e., P2, N2 activity) found in this study might reflect the attention orienting and cognitive control processes. MacLeod (2007) defined cognitive inhibition as "the stopping or overriding of a mental process, in whole or in part, with or without intention." In consideration of this definition, the present findings might reveal the role of inhibition in DF as attempting to suppress the ongoing encoding, although the TBF words were automatically processed.

There was a limitation to this paradigm. There were twice as many M cues as F cues in this study. In other words, for the participants, after the words were presented, the F cues showed a lower probability of occurrence relative to the M cues. Therefore, the magnitude of the cue effect (F cues vs. M cues) during the N2 epoch might be enhanced owing to this oddball effect, although the maximum oddball N2 difference distributed over the posterior rather than the anterior scalp (see the review by Folstein and Van Petten, 2008). Additionally, previous ERP studies employing the oddball paradigm demonstrated that rare stimuli evoked enhanced P3 and LPC activity relative to frequent stimuli (Campanella et al., 2002; Denecke et al., 2004). Therefore, the cue effect between F and M cues during the P3 and LPC time windows might also be affected by the oddball effect. Future studies could adjust the proportion of different trials to eliminate this oddball effect.

### CONCLUSIONS

This study aimed to compare the neural activity of maintenance rehearsal vs. DF. Compared with the M cue, the F cue evoked a decreased frontal P2 component and an enhanced frontal N2 component, indicating that DF is an active process that involves a frontal control process. In addition, DF might be more effortful relative to maintenance rehearsal. Furthermore, the cognitive control process might play an important role in intentional forgetting.

#### AUTHOR CONTRIBUTIONS

HG and MQ: designed the experiment. HG: conducted the experiment and analyzed the data. HG and MQ: wrote the

#### REFERENCES

manuscript. All authors edited and revised manuscript and approved final version of manuscript.

#### FUNDING

This study was supported by the National Natural Science Foundation of China (Grants 30970888).

#### ACKNOWLEDGMENTS

We would like to thank Jiazhan Wang for his help in collecting data.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2018 Gao, Qi and Zhang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# No Gender Differences in Egocentric and Allocentric Environmental Transformation After Compensating for Male Advantage by Manipulating Familiarity

Raffaella Nori 1 \*, Laura Piccardi 2,3, Andrea Maialetti 4 , Mirco Goro4 , Andrea Rossetti 4 , Ornella Argento4 and Cecilia Guariglia3,4

1 Department of Psychology, University of Bologna, Bologna, Italy, 2 Life, Health and Environmental Science Department L'Aquila University, L'Aquila, Italy, 3 Neuropsychology Unit, IRCCS Santa Lucia Foundation, Rome, Italy, 4 Department of Psychology, University of Rome, Rome, Italy

#### Edited by:

Alfredo Meneses, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional (CINVESTAV-IPN), Mexico

#### Reviewed by:

Zoltan Nadasdy, NeuroTexas Institute and Research Foundation, United States Aaron Wilber, Florida State University, United States

> \*Correspondence: Raffaella Nori<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Neuropharmacology, a section of the journal Frontiers in Neuroscience

Received: 01 August 2017 Accepted: 14 March 2018 Published: 28 March 2018

#### Citation:

Nori R, Piccardi L, Maialetti A, Goro M, Rossetti A, Argento O and Guariglia C (2018) No Gender Differences in Egocentric and Allocentric Environmental Transformation After Compensating for Male Advantage by Manipulating Familiarity. Front. Neurosci. 12:204. doi: 10.3389/fnins.2018.00204 The present study has two-fold aims: to investigate whether gender differences persist even when more time is given to acquire spatial information; to assess the gender effect when the retrieval phase requires recalling the pathway from the same or a different reference perspective (egocentric or allocentric). Specifically, we analyse the performance of men and women while learning a path from a map or by observing an experimenter in a real environment. We then asked them to reproduce the learned path using the same reference system (map learning vs. map retrieval or real environment learning vs. real environment retrieval) or using a different reference system (map learning vs. real environment retrieval or vice versa). The results showed that gender differences were not present in the retrieval phase when women have the necessary time to acquire spatial information. Moreover, using the egocentric coordinates (both in the learning and retrieval phase) proved easier than the other conditions, whereas learning through allocentric coordinates and then retrieving the environmental information using egocentric coordinates proved to be the most difficult. Results showed that by manipulating familiarity, gender differences disappear, or are attenuated in all conditions.

Keywords: gender differences, allocentric frames of reference, egocentric frames of reference, change of perspective, learning time

# INTRODUCTION

Human beings orient themselves through the environment by using different strategies to represent the space. The notion of "frame of reference" refers to the way in which individuals represent landmarks and their spatial location as well as their own position with respect to the environmental objects.

In spatial cognition, individuals may use two different spatial frames of references: "egocentric" (body-centered) and "allocentric" (world-centered) (Burgess, 2006, 2008; Arleo and Rondi-Reig, 2007). Specifically, an individual may locate environmental features by (a) referring to his own position, namely an egocentric frame of reference or (b) referring to the spatial and configurational properties of environmental features, namely an allocentric frame of reference (Galati et al., 2000; for a review see Avraamides and Kelly, 2008).

For example, when individuals actually navigate through an environment they memorize spatial locations considering them with respect to their position, whereas when they plan or study a path by observing it on a map they represent the space regardless of their own position. Both humans and animals form an environmental representation by integrating internal cues (e.g., self-motion; proprioceptive information; visual cues) with external ones (e.g., the relationships between environmental landmarks; positional and directional environmental cues: Cheng, 1986; Jacobs and Schenk, 2003). Therefore, the "maplike" environmental representation depends on egocentric and allocentric reference frames and the continuous translation of information coming from these two systems.

According to Wolbers and Hegarty (2010), spatial navigation requires three essential elements: (1) Spatial cues, (2) Computational mechanisms, and (3) Spatial representations. Spatial cues have a role in extracting information about our own position in the environment. They might refer to either environmental cues (i.e., such as landmarks, geometric structure of the environment) or self-motion cues (i.e., such as proprioceptive, vestibular, and motion cues). Computational mechanisms include both spatial computations and more general executive processes. On the one hand, spatial computations include space perception, translating between egocentric and allocentric frames of reference, computing distance and directions toward an invisible goal, imagining shifts in spatial perspective. On the other hand, executive processes involve novelty detection, selection, and maintenance of the navigational goal, route planning, and conflict resolution. Spatial representations include both offline and online spatial representations. Most of the models of human spatial navigation focused on the attributes of the spatial representations, that is the way in which spatial knowledge is organized.

As pointed out by Mou et al. (2006), a path requires the computation of a precise self-to-object spatial relation to guide locomotion, while planning a route to a distant goal and maintaining a sense of direction in a large-scale environment requires object-to-object spatial relation. The egocentric frame of reference considers the body as the center of the environmental organization so the spatial mental representation is biased by the relation between the body's position and the spatial location. On the contrary, the allocentric frame of reference is specified independently of the body's position (e.g., Waller et al., 2002). As a consequence, during navigation, individuals process egocentric and allocentric environmental cues that have a role in building and retrieving topographic long-term memory. Contemporary models of human spatial memory and navigation attempt to specify the role of both egocentric and allocentric information. Wang and Spelke, (2000, 2002) suggested that spatial memory was solely supported by egocentric references. Specifically, they suggested the existence of two stages, namely an egocentric process and a geometric module. The former involves a viewpoint-dependent scene recognition and a spatial updating of location by self-motion information whereas the latter has no role in representing locations but only in representing the geometry of the environment in spite of the individual's position. From this point of view, an allocentric frame of reference is not openly considered, if not with the purpose to support reorientation when the path integration system (i.e., the capacity to use cues generated by one's own movements to update one's position in the environment) breaks down. However, experimental data indicate a "two-system" model of parallel egocentric and allocentric representations in memory (e.g., Burgess et al., 2001; Burgess, 2006; Waller and Hodgson, 2006). Mou et al. (2004) proposed another model of spatial memory and navigation including an egocentric and an environmental subsystem. The former computes and represents the transient self-to-object spatial relations needed for locomotion, and decays rapidly in the absence of perceptual input or rehearsal. The latter, instead, is responsible for representing the characteristics of a familiar environment in an orientation-dependent manner. Both subsystems are based on an intrinsic reference system (e.g., Shelton and McNamara, 2001).

Researchers taking into account the role played by the reference systems in several actions hypothesize that they may form specialized cognitive mechanisms that rely on specific neural networks. In particular, it appears that the hippocampus and the medial temporal lobe provide allocentric environmental representations, while the parietal lobe provides egocentric representations, and the retrosplenial cortex and parietooccipital sulcus allow both types of representation to interact (for a review see, Burgess, 2008).

From a neural point of view, several studies have shown that egocentric navigation is sub-served by a set of areas related to landmark knowledge (i.e., the parahippocampal place area, Epstein and Ward, 2010), egocentric spatial representation by the parietal cortex (i.e., precuneus and cuneus, inferior parietal lobe) and heading information by the retrosplenial cortex. Instead, allocentric navigation seems mainly related to the hippocampal cortex (Tolman, 1948; O'Keefe and Nadel, 1978; Maguire et al., 1998). Moreover, fMRI studies have shown activations in the hippocampal formation, parietal cortex and retrosplenial regions during tasks involving both egocentric (Galati et al., 2000; Wolber et al., 2004; Latini-Corazzini et al., 2010) and allocentric (Iaria et al., 2007; Latini-Corazzini et al., 2010) frames of reference.

In addition, an ALE meta-analysis by Boccia et al. (2014) demonstrated that the allocentric and egocentric frames of reference were subtended by the same areas, but the latter elicits greater activation in the right precuneus, middle occipital lobe, and angular gyrus.

Studies that investigate the use of egocentric and allocentric frames of reference assume that they are determined mainly by innate factors such as gender (e.g., Chai and Jacobs, 2010), age (e.g., Moffat and Resnick, 2002), or familiarity (e.g., Nori and Piccardi, 2011, 2012). Other studies have considered that the egocentric and allocentric frames of reference may also be affected by external factors such as stimulus salience (e.g., Wolbers and Hegarty, 2010), the availability of landmarks or the experience with these stimuli (Wolbers and Hegarty, 2010). Furthermore, the type of navigational tasks elicits the use of one system rather than the other. For example, route learning tasks elicit egocentric coordinates (e.g., Nemmi et al., 2013), while place learning tasks elicit allocentric ones (e.g., Woolley et al., 2010). However, some studies have revealed that people are able to switch between the two different frames of reference (e.g., Iaria et al., 2003; Etchamendy and Bohbot, 2007; Iglói et al., 2009). Recently, Livingstone-Lee et al. (2014) have studied the effects of performing allocentric and egocentric training in men and women for a subsequent spatial task in which the use of both allocentric and egocentric frames of reference were equally efficient. The results showed no evidence of gender differences in the use of egocentric/allocentric coordinates and in navigation performance, suggesting that individuals may be trained to use one system rather than another. Piccardi et al. (2011a) showed that gender differences in the use of egocentric and allocentric references emerge only in adverse learning conditions when the task requires high spatial skills.

Altogether these studies raise the important issue of needing to deepen our knowledge on what factors might influence the use of ego/allocentric coordinates.

There is also evidence that memories for pathways are viewpoint dependent. As spatial information is encoded according to an orientation-dependent view, the original learning perspective constitutes the primary frame of reference irrespective of the use of egocentric or allocentric coordinates (e.g., Presson and Montello, 1994; Sholl and Nolin, 1997; Shelton and McNamara, 2001). As Piccardi et al. (2011a) pointed out, there is little agreement about which factors are important in attenuating or eliminating orientation-dependent path representations: some studies highlight the environmental characteristics of the path that people have to acquire and remember (e.g., Sholl and Nolin, 1997) whereas others focus on the strategy used for acquiring spatial information (e.g., Rossano et al., 1995; Nori et al., 2006). Piccardi et al. (2011a) observed that when people have the possibility to learn a path without a time limit, basing their strategies on egocentric coordinates, both men and women are good at performing directional judgments irrespective of the learning orientation. In this work, the authors investigated the ability of 106 (55 males, 51 females) college students to recall an 8-step path from different viewpoints after moving directly on the path or by studying the same layout printed on a map. Participants did not have any time limit during the Learning phase. For each participant, authors computed the time and the number of repetitions necessary to learn the path.

Results showed that by allowing longer duration of familiarization and more practice repetitions for females than males markedly reduced the gender difference (for details see Piccardi et al., 2011a). For such a reason, in the present study we have set a time limit corresponding to 3 min and 1 s for men and 3 min and 30 s for women and a number of repetitions corresponding to three times for men and four times for women, adopting the same means and standard deviations obtained by participants in Piccardi et al. (2011a).

This is true also during navigation in virtual environments (Nori et al., 2015a,b).

The aim of the present study was to investigate the presence of gender differences in learning a pathway in different frames of reference (ego/allocentric) and in translating from one frame of reference to another, considering the different time of familiarization for men and women. We also hypothesize that women perform better and more quickly in egocentric as opposed to allocentric frames of reference. Specifically, we hypothesized that adopting the same frame of reference assumed during the learning phase also in the retrieval phase may make participants more accurate and faster in recalling the previously learnt pathway. Vice versa, translating spatial information learnt in one frame of reference to another may affect the accuracy and speediness in the recalling of the learnt path. With respect to gender, we also expected that the translating computation from one frame of reference to another would be more difficult for women than men. A secondary aim of this work was to analyze if increasing the familiarity with the experimental setting (acting through the exposure time to the map or the number of repetitions of the path in the real environment) may produce an improvement in the performance making it easier to translate from one frame of reference to another.

# METHOD

# Participants

The study involved 160 College students (83 women), recruited in the Sapienza University of Rome, aged between 18 and 30 years (M = 24.91 years S.D. = 2.41 years; Men, M = 25.76 years, S.D. = 2.20 years; Women, M = 24.03 years, S.D. = 2.30 years). Thirteen participants were left-handed and eight ambidextrous (Salmaso and Longoni, 1983). Participants were randomly assigned to one out of four experimental conditions, namely: egocentric frame of reference condition (EC), 40 participants (20 women); allocentric frame of reference condition (AC), 41 participants (21 women); egocentric/allocentric frames of reference condition (EAC), 42 participants (22 women) and allocentric/egocentric frames of reference condition (AEC), 37 participants (20 women). This study was carried out in agreement with the Declaration of Helsinki with written informed consent from all subjects. The protocol was approved by the Local Ethical Committee of the Sapienza University.

# APPARATUS AND PROCEDURE

# Condition 1. EC

#### Egocentric Learning Phase

Each participant was tested individually. We used an enlarged version of the WalCT (Piccardi et al., 2008, 2013), that is the M-WalCT (used in Piccardi et al., 2011b, 2014, 2016; Nori et al., 2015a,b) in which 18 squares (3 × 3 cm) are placed on a carpet (5 × 6 m) in a scattered array (**Figure 1A**). To induce route acquisition, the four cardinal points (i.e., North, South, East, West) are indicated outside the carpet. The walls are completely covered with curtains that hide all external landmarks (i.e., doors, heaters, etc.). In this learning condition, participants had to learn four different 8-step sequences. The experimenter demonstrated each sequence by walking on the carpet and stopping on each square for 2 s. On the basis of the findings of Piccardi et al. (2008, 2011a,b), which showed that women require more time to acquire a path than men, and in accordance with Piccardi et al. (2011b,

2014), we considered different times of learning for men and women: the experimenter demonstrated each path three times for men and four times for women. Blindfolded participants were seated in a wheelchair located at the end of the room and were then wheeled, unblindfolded, toward the path. Each participant was then asked to stand up and was taken to the beginning of the path where s/he was led by the experimenter along eight different squares. At the end of each path, the participant was re-seated in the wheelchair and wheeled in a random and meandering route back to the initial location for his/her next walk along the same path, until it had been followed three times for men and four for women. Each walk took ∼40 s. Each participant learned four paths and was tested in eight different angle degrees for each path for a total of 32 trails.

#### Egocentric Testing Phase

After the learning phase, the participants were pushed in the wheelchair again and, unblindfolded, placed in front of the path and were asked to reproduce the path they had learned before in the same or in different perspectives (0◦–45◦–90◦–135◦–180◦– 225◦–270◦–315◦ ) by walking on the layout. Specifically, the participant was placed in front of the layout in the which s/he had to reproduce the path. The order of the different degrees of reproduction was determined randomly for each path and then the same order was used for all participants (Nori et al., 2006). For each path, the experimenter recorded the points/locations on the path correctly reproduced, that is points/locations in the exact sequence order. A hand-held stopwatch was used to record the planning time, that is the time elapsed before starting the path that had to be reproduced, and response time, that is the time people took to solve the task, including the planning time.

# Condition 2. AC

#### Allocentric Learning Phase

Each participant was tested individually. We used a map reproduction printed on an A4 sheet of paper of the M-WalCT used in EC, reproduced in 1:10 scale and the same four different 8-step sequences that the participants had to learn (see **Figure 1B**). On the basis of Piccardi et al. (2011b, 2014), we considered different times of learning for men and women: the experimenter demonstrated each path for 3 min and 1 s for men and 3 min and 30 s for women. Blindfolded participants were seated in a wheelchair located at the end of the room. They were then wheeled, unblindfolded, to a table where they found the first of four paths printed on the map and studied it for the amount of time established for men and women respectively. At the end of the learning phase on each map, the participant was re-seated in the wheelchair and wheeled in a random and meandering route back to the table. In spite of for the allocentric condition to perform participants' disorientation is useless, we have disoriented participants for making the experimental procedure comparable to that of the egocentric condition. Each participant learned four paths printed on a sheet of paper and was tested in eight different angle degrees for each path for a total of 32 trails.

#### Allocentric Testing Phase

After the learning phase, the participants were asked to reproduce with a pen the path they had previously learned from the same or different perspectives (0◦–45◦–90◦–135◦–180◦–225◦– 270◦–315◦ ) on a blank map, that is without the path printed on it. Specifically, the blank map was placed in front of the participant in the perspective from which s/he had to reproduce the path. To learn a path from a map requires an allocentric reference frame because it requires to process the whole path whereby the participant represents and updates his/her position in the environment. In such a way, generally, this kind of task is solved by using a reference system external to the body and anchored in the environment (see for example Klatzky, 1998). In such a reference system, the reference directions or axes are stable with respect to the local environment, that is the relationship among landmarks along a path without being centered on the body (Meilinger et al., 2014). We believe that learning a path from a map satisfies this constrain as a consequence we considered this task part of the allocentric testing phase.

The order of the different degrees of reproduction was determined randomly for each path and then the same order was used for all participants (Nori et al., 2006). For each path, the experimenter recorded the points/locations on the map correctly reproduced. A hand-held stopwatch was used to record the planning time, that is the time elapsed before starting the path that had to be reproduced, and response time, that is the time people took to solve the task, including the planning time.

# Condition 3. EAC

#### Egocentric Learning Phase

The learning phase was the same as in Condition 1, EC: participants had to learn four different 8-step sequences of the M-WalCT. The experimenter demonstrated each sequence by walking on the carpet and stopping on each square for 2 s (see **Figure 1C**); the experimenter demonstrated each path three times for men and four times for women. Blindfolded participants were seated in a wheelchair located at the end of the room and were then wheeled toward the path. The participant was then asked to stand up and was led to the beginning of the path, where s/he was led by the experimenter along eight different routes. At the end of each path, the participant was re-seated in the wheelchair and wheeled in a random and meandering route back to the initial location for his/her next walk along the same path, until it had been followed three times for men or four for women. Even in this case, each participant was submitted to a total of 32 trails.

#### Allocentric Testing Phase

After the learning phase, as in Condition 2 AC, the participants were asked to reproduce the path they had previously learned from the same or different perspectives (0◦–45◦–90◦–135◦– 180◦–225◦–270◦–315◦ ) on a blank map of the M-WalCT. The blank map was placed in front of the participant in the perspective from which s/he had to reproduce the path. The order of these different degrees of reproduction was determined randomly for each path and then the same order was used for all participants (Nori et al., 2006). For each path, the experimenter recorded the points/locations on the map correctly reproduced. A hand-held stopwatch was used to record the planning time, that is the time elapsed before starting the path that had to be reproduced, and response time, that is the time people took to solve the task, including the planning time.

# Condition 4. AEC

#### Allocentric Learning Phase

The learning phase was the same as for Condition 2, AC: the experimenter demonstrated each path printed on a map for 3 min and 01 s for men and 3 min and 30 s for women (see **Figure 1D**). Successively, blindfolded participants were seated in a wheelchair located at the end of the room. They were then wheeled to the table where they found the first of four paths. At the end of the learning phase on each map, the participant was seated in the wheelchair and wheeled in a random and meandering route back to the table. Even in this case, each participant was submitted to a total of 32 trails.

#### Egocentric Testing Phase

After the learning phase, as in Condition 1, EC: the participants were asked to reproduce the path they had previously learned on a map from the same or different perspectives (0◦– 45◦–90◦–135◦–180◦–225◦–270◦–315◦ ) by walking on the real environment. Participant was placed in front of the layout in the perspective from which s/he had to reproduce the path. As for the previous conditions, the order of these different degrees of reproduction was determined randomly for each path and then the same order was used for all participants (Nori et al., 2006). For each path, the experimenter recorded the points/locations on the path correctly reproduced. A hand-held stopwatch was used to record the planning time, that is the time elapsed before starting the path that had to be reproduced, and response time, that is the time people took to solve the task, including the planning time.

### RESULTS

We compared the four conditions considering a three-way analysis of variance with mixed designs with two levels of the between-variable "gender" (men/women), four levels of betweenvariable "condition" (EC – AC – EAC – AEC) and the 8 "degrees" of path reproduction as repeated factor (0◦–45◦–90◦–135◦– 180◦–225◦–270◦–315◦ ). As dependent variable we considered both the mean number of locations correctly reported (accuracy; minimum score = 0, maximum score = 8) and the response time (s.) for each degree (perspective) on the four paths. Both for accuracy and response time, we handled the data, and we averaged them for each participant. In order to analyse if the assumption of homogeneity of variance is met we performed the Levene test (Levene, 1960) on accuracy [0◦ : F(1, 158) = 3.99, p = 0.52; 45◦ : F(1, 158) = 0.05, p = 0.81; 90◦ : F(1, 158) = 0.01, p = 0.92; 135◦ : F(1, 158) = 0.19, p = 0.66; 180◦ : F(1, 158) = 0.03, p =.84; 225◦ : F(1, 158) = 0.06, p = 0.80; 270◦ : F(1, 158) = 0.17, p = 67; 315◦ : F(1, 158) = 0.24, p = 0.62], response time [0◦ : F(1, 158) =3.09, p = 0.08; 45◦ : F(1, 158) =0.1.29, p = 0.25; 90◦ : F(1, 158) = 1.40, p = 0.23; 135◦ : F(1, 158) = 0.00, p = 0.93; 180◦ : F(1, 158) = 1.10, p = 0.29; 225◦ : F(1, 158) = 2.55, p = 0.11; 270◦ : F(1, 158) = 1.48, p =0.22; 315◦ : F(1, 158) = 1.78, p = 0.18], and planning time [0◦ : F(1, 158) =3.20, p = 0.07; 45◦ : F(1, 158) = 0.1.51, p = 0.22; 90◦ : F(1, 158) = 4.71, p = 0.03; 135◦ : F(1, 158) = 1.35, p = 0.24; 180◦ : F(1, 158) = 1.28, p = 0.25; 225◦ : F(1, 158) = 1.20, p = 0.27; 270◦ : F(1, 158) = 7.29, p = 0.00; 315◦ : F(1, 158) = 7.22, p = 0.00]. The results show that the assumption of homogeneity of variance is met for accuracy and response time but not for some perspectives (angles) in planning time so we did not perform any further analysis on this variable.

# Number of Locations Correctly Reported (Accuracy)

The main effect of "gender" was not statistically significant [F(1, 152) = 0.66, p = 0.41, η 2 = 0.00; Men M: 5.93, S.D. = 0.19, Women M = 6.16, S.D. = 0.18], nor was the interaction "gender x condition" [F(3, 152) = 1.13, p = 0.33, η 2 = 0.02]. The main effect of "condition" was statistically significant [F(3, 152) = 10.77, p < 0.001, η 2 = 0.17]. Post-hoc Bonferroni revealed that the EC is easier than all the others (ps < 0.01: EC, M = 7.25 S.D. = 0.27; AC, M = 5.85 S.D. = 0.26; EAC, M = 6.03 S.D. = 0.26; AEC, M = 5.05 S.D. = 0.28). The main effect of "degrees" was statistically significant [F(7, 152) = 2.17, p = 0.01, η 2 = 0.01]. Post-hoc Bonferroni revealed that it is easier to remember a path from 315◦ (M = 6.18, S.D. = 0.37) than from 90◦ (M = 5.97, S.D. = 0.14) and 225◦ (M = 5.99, S.D. =.14). No other significant results were found. The interaction "condition x degrees" was statistically significant [F(21, 152) = 2.84, p < 0.001, η 2 = 0.17]. Specifically, post-hoc Bonferroni revealed that remembering a path in a real congruent condition (EC) is easier than in a map/real incongruent condition (AEC) for all perspectives (ps < 0.001). Moreover, remembering a path in a real congruent condition (EC) is easier than in a map congruent condition (AC) from 135◦ and 225◦ perspectives (see **Figure 2**). No other significant differences were revealed.

#### Response Time

The main effect of "gender" was statistically significant [F(1, 152) = 4.25, p < 0.05, η 2 = 0.02], men are faster than women (men, M = 19.96s., S.D. = 0.1.30s.; women, M = 22.70s., S.D.= 0.81.25s.). Moreover, the main effect of "condition" was also statistically significant [F(3, 152) = 13.68, p < 0.001, η 2 = 0.21]. Post-hoc Bonferroni showed that remembering a path in AC (M = 27.90s., S.D. = 1.78s.) was slower than in AEC (M = 11.97s, S.D. = 1.88s.) and EC (M = 19.63s., S.D. = 1.80s.). Moreover, the AEC is faster than EC and EAC (M = 23.82s., S.D. = 1.76s.). The main effect of "degrees" was statistically significant [F(7, 152) = 18.71, p < 0.001, η 2 = 0.11]: recalling a path from 225◦ -270◦ -315◦ is slower than all other degrees (p < 0.05).

The interaction "condition x degrees" was also statistically significant [F(21, 152) = 8.80, p < 0.001, η 2 = 0.14]. Specifically, post-hoc Bonferroni showed that remembering a path in the AEC is faster than in AC at 0◦–90◦–135◦–180◦ (ps < 0.01); remembering a path in AC is slower than in EC and EAC at 225◦ (ps < 0.05) while it is faster than in EC and in EAC at 0◦–135◦– 180◦ (ps < 0.05); remembering a path in AEC is faster than in EAC at 270◦ (p < 0.05). Descriptives are shown in **Figure 2**. No other significant differences are shown.

### DISCUSSION

To our knowledge, the present study was the first to investigate the presence of gender differences in retrieving environmental information learnt in the same or different frames of reference. In particular, our intent was to analyse whether the performance of men and women in retrieving a path from different points of view using the same reference both in the learning and retrieval phases is easier and faster than one in which different references are used. We also wanted to investigate whether gender differences could be reduced by increasing the familiarity with the experimental setting by manipulating the time of map exposure or the number of repetitions to learn a pathway.

Our results partially confirm our hypothesis. Gender differences in remembering a path correctly were absent in

both egocentric and allocentric reference frames. In particular, we found that by manipulating familiarity, gender differences disappeared or attenuated. This result differs from that of several studies in which men outperform women in perspective-taking tasks (e.g., for a review see Coluccia and Louse, 2004). However, in these studies men and women were exposed to the same short time to acquire spatial information. Already, Piccardi et al. (2011a,b) found that computing the individual learning time allows gender differences in perspective taking tasks to be eliminated. Therefore, also computational spatial operations like the transformation of spatial information from egocentric to allocentric frames of reference and vice versa do not elicit a gender effect. This supports the evidence that when spatial information is stored and consolidated, all individuals are able to process and re-elaborate it. This result is in line with studies which demonstrated that by increasing the familiarity with the environment even poor spatial navigators were able to perform very complex tasks: the higher the individuals' familiarity with the environment, the better their performances (Iachini et al., 2009; Nori and Piccardi, 2011; Piccardi et al., 2011a). Indeed, as pointed out by Montello (1998) additional locomotor and perceptual experience of the environment, as well as familiarity with the place, result in more extensive, complete, and accurate knowledge. So the two concepts are related and specifically, increasing learning time increases familiarity with the environment, thus allowing a more complete knowledge of the experimental environment. Our results are also in line with Iachini et al. (2009), who investigated how familiarity and gender have an effect even in the frames of reference used in memory to represent a real environment. Their results showed that males were more accurate and faster than females in detecting environmental changes, in particular when participants were unfamiliar with the environment. Considering that in our experiment, the degree of familiarity with the environment was measured in terms of the time necessary to learn the experimental array, we found that when time and repetitions are sufficient, women are as efficient as men. However, it is interesting that gender differences are still present in solving the task: men are quicker than women. Therefore, familiarity is important to eliminate gender differences in terms of accuracy but it is not sufficient to eliminate gender differences in response time. This result could be explained by considering the model of Coluccia and Louse (2004), who proposed that gender differences emerged according to the cognitive demand of the spatial tasks, which could be attributed to the visuo-spatial working memory load. Specifically, gender differences emerged only when tasks required a high integration and transformation of visually imagined material: given the necessary time to acquire spatial information females may rotate the path accurately even if they take longer than males to do so, since they are accurate but still slow in performing the mental rotation of the environment.

Another result that emerged from our study is that all participants showed the same level of accuracy in all perspectives they assumed to recall the path. In general, all preferred clockwise and right body axes starting positions with respect to counter clockwise and left body axes positions, probably because the participants were right-handed (see also: Sholl and Nolin, 1997). The time of response is predicted by the time employed to mentally process the cognitive map of the environment. In particular, we found that the planning time predicted some perspectives in terms of time of performance.

As far as the effect of learning and retrieval spatial information is concerned, using the same reference frame, we found that the egocentric frame of reference condition (EC) is the easiest for all participants in recalling a path from different perspectives, while the allocentric frame of reference condition (AC) resulted in a worse performance. This is in line with Wang and Spelke's model (Wang and Spelke, 2000, 2002), which suggests that the egocentric coordinates are the preferred system for both men and women, even if the use of allocentric coordinates could be not completely excluded, and it is possible that participants may simultaneously use an allocentric reference in which they themselves are the references for the spatial information (Burgess, 2006). Very likely, men are more proficient than Nori et al. No Gender Differences in Environmental Transformation

women in adverse learning conditions (e.g., temporal pressure or when the task requires a high cognitive load) (Coluccia and Louse, 2004; Lawton, 2010). Generally, in fact, during a complex environment exploration requiring a prolonged selfmotion, it is more efficient to maintain an allocentric map of the environment than to continuously update multiple egocentric representations. However, the translation between egocentric and allocentric information is not equal: it is much more difficult to translate from egocentric to allocentric information than vice versa. The translation between these two different systems of coordinates that requires translating action-oriented egocentric representations into allocentric representations (e.g., the body references right/left become environmental references north/south) determines a cost in terms of time (Iaria et al., 2003; Etchamendy and Bohbot, 2007; Iglói et al., 2009). However, data demonstrate that individuals are nevertheless able to switch from one representation to another also during navigation, suggesting that people have both egocentric and allocentric coordinates at their disposal, although it is generally agreed that allocentric representations are more cognitive demanding than egocentric ones. This is also supported by Siegel and White's model (1975) that suggests a cumulative and hierarchical organization of spatial knowledge with high-level stages encompassing features of the lower stages. For these authors, in order to have an allocentric representation of the environment it is necessary to have acquired the egocentric representation. This seminal model supports our results that demonstrate how learning and retrieving a path is easier through an egocentric frame of reference. Indeed, from this point of view, the egocentric reference is the first system that humans develop to move through the environment. The importance of starting from an egocentric first-person

#### REFERENCES

perspective representation is also assumed in the animal models of spatial navigation (O'Keefe and Nadel, 1979). Egocentric navigation, in fact, resembles Taxon navigation (O'Keefe and Nadel, 1979), whereas allocentric navigation resembles Place navigation (O'Keefe and Nadel, 1979). Moreover, Byrne and Becker (2008) focus on the fact that spatial information from the environment must reach the brain via sensory receptors in an inherently egocentric sensory representation.

To summarize, gender differences in spatial navigation performance are reduced when participants become familiar with the environment. In our case, the familiarity was acquired through the time of exposure to the map or the number of repetitions performed to learn the path. With a high level of familiarity participants are able to perform spatial tasks with a high cognitive load, such as the translating from one frame of reference to another. In general, participants show a preference and a better proficiency when learning occurs in egocentric frames of reference. Overall, these results indicate that interactions between environmental demands and cognitive processes compensate for gender differences in spatial navigation performance.

#### AUTHOR CONTRIBUTIONS

RN and LP: made substantial contributions to conception and design, participated in drafting the article, or revising it critically for important intellectual content; AM, MG, AR, and OA: made contributions to acquisition of data, and analysis and interpretation of data; CG: gave contributions in interpretation of data; final approval of the version to be submitted and any revised version.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2018 Nori, Piccardi, Maialetti, Goro, Rossetti, Argento and Guariglia. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.


*Edited by Manisha Sahay*

The first section of the book covers the basics of nephrology and second section focuses on acute kidney injury. This easy to reference text examines the physiological and biochemical aspects of renal diseases - all in one convenient resource. Experts in the field discuss topics of increasing concern in nephrology including newer methods of assessing renal function. The field of acute kidney injury in nephrology is a rapidly evolving one with research translating into clinical guidelines and standards. This text brings together experts to provide an authoritative reference for management of AKI in various clinical settings. Pregnancy related AKI is an important entity which has also been discussed in detail. The recent advances in the field of critical care AKI have been incorporated as well and help the reader to update their knowledge.

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Basic Nephrology and Acute Kidney Injury

Photo by creativenv / iStock


**4. Conclusions**

In this paper, we investigated the effect of Aβ monomers on the mechanical properties of the POPC vesicle. Additionally, we have investigated the change in basic membrane parameters, such as membrane thickness and APL. We showed that membrane thickness increases and APL decreases after the incorporation of Aβ. We postulate that this results from the bilayer's mechanical remodeling after Aβ monomer incorporation reported previously in the literature. We observed a decrease in the bending rigidity coefficient after incorporating Aβ in both MD simulation and the flicker-noise experiment. Since it was reported in the literature that Aβ-induced membrane remodeling is more likely when bending rigidity is smaller, we believe that the progressing decrease of bending rigidity might be considered a driving factor of neurodegeneration progression. We managed to prove that incorporating Aβ peptides influences the mechanical properties of lipid membranes, suggesting that membrane's mechanical properties may play a more important role in neurodegenerative disorders. Finally, we have investigated the difference in wave propagation on membranes with and without incorporated Aβ peptides. We showed that the presence of the peptides did change the behavior of the system. This could lead to an impediment of nerve impulse propagation and/or shift in membrane resonance frequency and, as a result, disrupt gamma oscillations. In summary, this paper aims to draw attention to an important hypothesis that mechanically driven molecular phenomena that originate from the membrane could be a critical factor in the pathogenesis of AD. We believe that we presented satisfactory results to support this claim. We acknowledge that this study was limited to the effect on POPC lipid membrane only. Further studies should be focused on more biologically relevant membranes, specifically on the disruption of their ability to cluster dynamically. The effect of mechanical changes on lipid metabolism/signaling should also be addressed in future studies.

**Supplementary Materials:** Supplementary materials can be found at https://www.mdpi.com/14 22-0067/22/1/18/s1, Supporting Information: (1) Peptide incorporation into planar POPC bilayer, (2) System setup for POPC vesicles with incorporated peptides, (3) Verification of Aβ incorporation in GUVs, (4) Bending rigidity measurements using flicker-noise spectroscopy.

**Author Contributions:** Conceptualization, D.D. and S.K.; methodology, D.D. and G.C.; software, D.D.; validation, D.D.; formal analysis, D.D.; investigation, D.D.; resources, D.D.; data curation, D.D.; writing—original draft preparation, D.D.; writing—review and editing, G.C. and S.K.; visualization, D.D.; supervision, S.K.; project administration, D.D.; funding acquisition, D.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was possible thanks to the financial support from the National Science Centre (Poland) grants Nos. 2016/21/N/NZ1/02767 and 2018/30/E/NZ1/00099.

**Data Availability Statement:** Most of the data is available in the manuscript supplementary information. The simulation data presented in this study are available on request from the corresponding author. This data are not publicly available due to GBs files sizes.

**Acknowledgments:** Numerical resources for Molecular Dynamics simulations were granted by Wroclaw Centre of Networking and Supercomputing, grant No. 274.

**Conflicts of Interest:** The authors declare no conflict of interest.


**8. Antenatal care for women with suspected/confirmed covid-19**

Care of symptomatic pregnant women suffering from Covid-19 should be a multidisciplinary team approach.

American College of Obstetricians & Gynaecologists (ACOG) has developed an algorithm for management of outpatient pregnant women with suspected or confirmed COVID-19. If a woman has no symptoms to suggest infection with SARS-CoV2, she should receive routine prenatal care. If she has symptoms, severity of symptoms should be assessed. Assessment of severity of illness should include any shortness of breath, coughing up blood, dizziness, chest pain, not being able to keep down fluids and any history of confusion. If any of these are present, pregnant woman is at elevated risk and should be asked to seek care in an emergency department in a centre that has facilities for antenatal and obstetric care. If the woman has symptoms but those are not severe, she should be screened for any co-morbidities and any obstetric complications. If any co-morbidities or obstetric complications are present, she is categorised as having moderate risk and should be evaluated in ambulatory setting as soon as possible and should be investigated for severity of illness. CT Scan with abdominal shielding should be done if clinically indicated. If the woman does not have any high risk factors, she should be sent for symptomatic care at home, including hydration and rest and evaluated repeatedly for development of any of the above symptoms [26].

Indian Council of Medical Research (ICMR) recommends that symptomatic women with fever >38°C and respiratory symptoms should be hospitalised in a tertiary care centre with facilities for maternal and fetal monitoring. Seriousness of maternal situation is assessed by quick SOFA score, parameters of severity being systolic blood pressure < 100 mmHg, respiratory rate > 22, and Glasgow consciousness scale <15. Any pregnant woman with more than one of these factors should be admitted in Intensive Care Unit (ICU) [27].

FIGO recommends anomaly scan at 18–23 weeks in women with confirmed SARS-CoV2 infection and monthly scan after that for fetal growth. ICMR (Indian Council for Medical Research) recommends a growth scan 14 days after recovery from acute illness [25].

#### **9. Management during labor**

#### **9.1 Preparation before admission**

Admission for labor and delivery represents a unique scenario in that admission, though planned, cannot be delayed. The basic principles remain the same as those for outpatient visits, i.e., to avoid unnecessary hospital visits, maintain social distancing and other measures to prevent spread of SARS-CoV2. Women should be advised to quarantine themselves or work from home at least 14 days before planned admission for delivery or caesarean. This should start in most women by 37 weeks of gestation. Woman and her birthing partner should be screened for symptoms of COVID-19 telephonically one day before admission [28].

#### **9.2 Screening on arrival**

All women arriving for admission for delivery should be screened verbally for fever, cough and respiratory symptoms. Birthing partner should be similarly screened. Those testing positive should be sent for testing and care by Obstetric care

#### *Pregnancy and COVID-19 DOI: http://dx.doi.org/10.5772/intechopen.98710*

provider. Some women would already be diagnosed with SARS-CoV2 infection and they should directly be delegated to area dedicated for infected patients.

Case can be made for testing all women at the time of admission to labor and delivery unit because of high number of asymptomatic infections [20]. Local guidelines could also mandate testing at the time of admission.

After screening at the time of admission, women will be categorised into one of the three categories: infected, suspect and non-infected. Under ideal circumstances, all health care facilities caring for pregnant women should have well demarcated zones with separate passageways for all of these categories. These zones should include separate wards, intensive care areas and operation theatres. If not possible, all care should be taken to avoid infected and non-infected people coming in proximity of each other.

#### **9.3 General precautions during admission**

All women and their birthing partners should wear triple layer surgical masks throughout admission. All healthcare providers should wear triple layer surgical mask for each patient contact. Hands should be sanitised with alcohol based handrub after every patient contact. Droplet precautions should be used when caring for women with respiratory symptoms. This requires the use of gloves, gown, surgical mask and face shield. Gown, gloves, face shield and N95 mask should be used for any woman with suspected COVID and during any aerosol generating procedure including second stage of labour [28]. Disinfection of rooms should be done between patients.

Women should be allowed to have one birthing partner who should stay throughout admission. Other support persons should be given option to provide support through video. Visitors should not be allowed in person, although visitation may be considered in end of life situations.

Shifting of woman from one area to other should be avoided and all efforts should be made to provide services at women's bedside.

All preoperative investigations needed for caesarean should also be done on the day of admission to decrease the number of pre-admission hospital visits.

#### **9.4 Intrapartum care**

Management of first stage of labour remains essentially the same as in a woman not infected with Covid-19. Women with mild disease require management of fluidelectrolyte balance during labor, in addition to symptomatic management and close monitoring of maternal well-being. Woman should be encouraged to take oral fluids to maintain hydration. Intravenous fluids should be used with caution because of association of Covid-19 with Acute Respiratory Distress Syndrome (ARDS) [25]. Early use of oxytocin for slow and dysfunctional labour is recommended to avoid the stress and complications of a prolonged labor. Use of Nitrous Oxide during labour should be avoided because of insufficient data about cleaning, filtering and potential aerosolization of nitrous oxide systems [28].

Oxygen is used intrapartum for fetal benefit, to increase fetal oxygenation. A recent meta-analysis has shown that it does not provide fetal benefit and may even be harmful [29, 30]. ACOG recommends against the use of oxygen therapy for fetal resuscitation during labour [28].

Second stage of labour is considered an aerosol generating procedure and should be managed with appropriate precautions. Obstetric management remains the same as before the pandemic.

Blood resources have become scarce during the pandemic because of inability to conduct donation drives. Maintaining pre-delivery haemoglobin is the most efficient way to decrease the use of blood during labour and delivery admissions. Utmost importance should be given to aggressively treat anaemia detected during pregnancy. Blood transfusion should only be used when absolutely necessary and in minimum quantity.

Misoprostol and tranexamic acid should be used prophylactically in third stage of labor to decrease blood loss after delivery.

#### **10. Management of pregnant woman with COVID-19**

A pregnant woman with SARS-CoV2 infection should be counselled about the risk of serious infection and the methods to protect family members from infection. Next step is to assess systemic status of woman for severity of infection and need of hospitalisation.

Management of infection should be same as management of non-pregnant patients with COVID-19. If the patient needs hospitalisation, she should be admitted in a facility where maternal as well as fetal monitoring can be done [31]. The facility should be able to provide fetal and uterine contraction monitoring, individualised delivery planning and team based approach including obstetrician, paediatrician, anaesthetist and respiratory medicine specialist. The basic principles and medications remain the same as in non-pregnant patients. Potentially effective treatment for COVID-19 should not be withheld from pregnant women due to theoretical concerns regarding safety. Decisions regarding treatment options should be made keeping in mind safety of the medication, the severity of maternal disease and in shared decision-making with the patient [31].

A very important limitation is exclusion of pregnant women from most clinical trials involving new treatment modalities and the safety data remains scarce.

In most cases, timing of delivery should not be altered by maternal COVID-19 infection [32]. Patients who get infected in early pregnancy and subsequently recover do not require any change in the timing of delivery. For patients who contract SARS-CoV2 infection in the third trimester of pregnancy, attempt should be made to postpone delivery till negative SARS-CoV2 report or lifting of quarantine status to decrease the risk of perinatal transmission. Maternal COVID-19 infection is not an indication for caesarean section, which should be done for obstetric indication or on maternal request [32]. Because the risk of transmission from umbilical cord blood is low, delayed cord clamping should be continued as pre-pandemic. Similarly, umbilical cord blood banking can be done if the parents desire.

#### **11. Lactation and COVID-19**

Several studies have detected SARS-CoV2 nucleic acid in breast milk. However, infectious virus particles have not been detected in breast milk [33]. Also, antibodies specific to SARS-CoV2 have also been detected in breast milk, which could potentially protect the neonate. Therefore, it is recommended to continue breastfeeding in mothers with SARS-CoV2 infection, with precautions. These precautions include hand hygiene before breast feeding and wearing a face mask. Breast milk may be expressed after hand-hygiene and fed to infant by uninfected care-provider after disinfection (pasteurisation) [33].


**3. Tetradentate platinum(II) emitters**

#### **3.1 Platinum(II) porphyrin complexes**

The first photophysical studies of Pt(II) porphyrins were reported in the early 1970s and were triggered by the physicochemical relevance of metalloporphyrins such as chlorophyll, haem, and vitamin B12, which serve key biological functions [23]. This class of complexes is known for their high stability against heat, solvents, and extreme pH as a result of the strong coordination of Pt(II) ions in rigid porphyrin scaffolds. Pt(II) porphyrins exhibit intense absorptions in the visible region, and their electronic spectra are characterized by a Soret band at approximately 400 nm and two Q bands between 500 and 600 nm, which are attributed to porphyrin-centered 1 π-π\* electronic transitions. The triplet formation yields for Pt(II) porphyrins were reported to be close to unity due to an ultrafast intersystem crossing process that occurs on a sub-ps time scale [24]. These complexes typically display strong saturated red to near infrared (NIR) phosphorescence, depending on the structures of macrocycles, with long decay times of tens of microseconds under anaerobic conditions because the emissive excited state is essentially 3 LC (3 π, π\* ) in nature localized in the porphyrin ligand. For this reason, the emission properties can be rationally tuned by modifying the porphyrin ligands.

In 1998, Thompson and Forest reported the first use of a Pt(II) porphyrin complex, **Pt-1**, in electrophosphorescent devices (**Figure 2**) [18], which generated saturated red EL emission at 650 nm with a peak internal quantum efficiency (IQE) of 23%. Since then, the development of Pt(II) porphyrin complexes as phosphorescent emitters has attracted considerable interest [25–27].

Che et al. found that with the introduction of electron-deficient pentafluorophenyl rings at the meso positions of the porphyrin scaffold, **Pt-2** exhibited superior stability against oxidative degradation relative to that of the parental complex [Pt(TPP)] (TPP = 5,10,15,20-tetraphenylporphyrinato) (**Figure 2**) [28]. Saturated red (λmax = 647 nm) porphyrin-centered phosphorescence with a long lifetime (τem = 60 μs) was observed for **Pt-2** in CH2Cl2 at room temperature. Saturated red OLED devices with different doping concentrations of **Pt-2** have

**167**

**Figure 2.**

*Tetradentate Platinum(II) Emitters: Design Strategies, Photophysics, and OLED Applications*

been characterized. The EL spectra showed emission maxima at 655 nm, similar to that of the photoluminescent (PL) spectrum. At low driving voltages, emission from the host was not detected, indicating nearly complete energy transfer from the host. When a high voltage was applied, a blue emission from the host was observed, and its intensity increased with the driving voltage, which could be attributed to the saturation effect due to the long emission decay time of **Pt-2**. The efficiency increased until the dopant ratio reached 8% but decreased when the ratio was increased beyond 8%, which was rationalized by intermolecular quenching

Wang and co-workers designed a group of platinum(II) porphyrin dendrimers (**Pt-3**–**5**) [29] with different alkyl chain lengths to adjust the distance between the Pt porphyrin core (the emissive center) and side carbazole groups (hole- and energy-transfer fragments) (**Figure 2**) and systematically investigated intra- and intermolecular energy-transfer mechanisms. In solution, both fluorescence at 357 nm from the carbazole moieties and phosphorescence at 660 nm from the Pt(II) porphyrin core were observed. The carbazole emission disappeared when doped in a solid matrix, indicating an efficient energy-transfer process. Intramolecular energy-transfer was facilitated by reducing the distance between the emitting core and the side carbazole groups. Solution-processed EL devices based on **Pt-3** were fabricated with a structure of [ITO/poly(styrenesulfonate)-doped poly(3,4-ethyle nedioxythiophene)/**Pt-3**/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/ tris-(8-hydroxyquinoline)aluminum (Alq3)/Ca/Al] to evaluate the optoelectronic

660, and 720 nm was observed. The strong vibronic emission peaked at 660 was attributed to phosphorescence from the Pt(II) porphyrin cores, while the minor high-energy emission bands at 540 and 590 nm were suggested to be derived from thermally populated triplet states ("hot bands") or singlet states generated by TTA.

) with emission maxima at 540, 590,

processes due to the high density of triplet excitons.

*Chemical structures of platinum(II) porphyrin complexes Pt-1–8.*

properties. Bright phosphorescence (600 cd/m2

*DOI: http://dx.doi.org/10.5772/intechopen.93221*

*Tetradentate Platinum(II) Emitters: Design Strategies, Photophysics, and OLED Applications DOI: http://dx.doi.org/10.5772/intechopen.93221*

**Figure 2.** *Chemical structures of platinum(II) porphyrin complexes Pt-1–8.*

been characterized. The EL spectra showed emission maxima at 655 nm, similar to that of the photoluminescent (PL) spectrum. At low driving voltages, emission from the host was not detected, indicating nearly complete energy transfer from the host. When a high voltage was applied, a blue emission from the host was observed, and its intensity increased with the driving voltage, which could be attributed to the saturation effect due to the long emission decay time of **Pt-2**. The efficiency increased until the dopant ratio reached 8% but decreased when the ratio was increased beyond 8%, which was rationalized by intermolecular quenching processes due to the high density of triplet excitons.

Wang and co-workers designed a group of platinum(II) porphyrin dendrimers (**Pt-3**–**5**) [29] with different alkyl chain lengths to adjust the distance between the Pt porphyrin core (the emissive center) and side carbazole groups (hole- and energy-transfer fragments) (**Figure 2**) and systematically investigated intra- and intermolecular energy-transfer mechanisms. In solution, both fluorescence at 357 nm from the carbazole moieties and phosphorescence at 660 nm from the Pt(II) porphyrin core were observed. The carbazole emission disappeared when doped in a solid matrix, indicating an efficient energy-transfer process. Intramolecular energy-transfer was facilitated by reducing the distance between the emitting core and the side carbazole groups. Solution-processed EL devices based on **Pt-3** were fabricated with a structure of [ITO/poly(styrenesulfonate)-doped poly(3,4-ethyle nedioxythiophene)/**Pt-3**/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/ tris-(8-hydroxyquinoline)aluminum (Alq3)/Ca/Al] to evaluate the optoelectronic properties. Bright phosphorescence (600 cd/m2 ) with emission maxima at 540, 590, 660, and 720 nm was observed. The strong vibronic emission peaked at 660 was attributed to phosphorescence from the Pt(II) porphyrin cores, while the minor high-energy emission bands at 540 and 590 nm were suggested to be derived from thermally populated triplet states ("hot bands") or singlet states generated by TTA.

*Liquid Crystals and Display Technology*

butions are not mentioned herein.

to porphyrin-centered 1

**3. Tetradentate platinum(II) emitters**

**3.1 Platinum(II) porphyrin complexes**

quenching (ACQ ). Therefore, the appropriate management of intermolecular interactions/aggregation by modulating the 3D morphology and electromagnetic properties of the complexes is crucial in the molecular design of Pt(II) emitters for specific OLED applications in order to achieve optimum device performances (i.e.,

In the context of ligand architecture, the employment of tetradentate ligands in the design of platinum(II) emitters has clear advantages in terms of both chemical and thermal stabilities and luminescent efficiency compared to their bidentate and tridentate ligand counterparts. Tetradentate ligands provide a more stable scaffold for the coordination of platinum by offering the strong chelation effect, which could suppress ligand dissociation and demetalation. In addition, the rigid tetradentate ligand framework could largely restrict the excited-state metal-ligand structural distortion that in turn facilitates radiative deactivation of the emissive

high color purity, device efficiency, and long operational lifetime).

excited state, boosting the emission quantum yield of the Pt(II) emitter.

This chapter aims to provide an overview of mononuclear Pt(II) emitters containing tetradentate ligands reported in the literature. To keep the chapter to a reasonable size, we restrict our discussions to several selected classes of tetradentate platinum(II) emitters and apologize to the contributors to this field whose contri-

The first photophysical studies of Pt(II) porphyrins were reported in the early 1970s and were triggered by the physicochemical relevance of metalloporphyrins such as chlorophyll, haem, and vitamin B12, which serve key biological functions [23]. This class of complexes is known for their high stability against heat, solvents, and extreme pH as a result of the strong coordination of Pt(II) ions in rigid porphyrin scaffolds. Pt(II) porphyrins exhibit intense absorptions in the visible region, and their electronic spectra are characterized by a Soret band at approximately 400 nm and two Q bands between 500 and 600 nm, which are attributed

Pt(II) porphyrins were reported to be close to unity due to an ultrafast intersystem crossing process that occurs on a sub-ps time scale [24]. These complexes typically display strong saturated red to near infrared (NIR) phosphorescence, depending on the structures of macrocycles, with long decay times of tens of microseconds under

nature localized in the porphyrin ligand. For this reason, the emission properties

In 1998, Thompson and Forest reported the first use of a Pt(II) porphyrin complex, **Pt-1**, in electrophosphorescent devices (**Figure 2**) [18], which generated saturated red EL emission at 650 nm with a peak internal quantum efficiency (IQE) of 23%. Since then, the development of Pt(II) porphyrin complexes as phosphores-

Che et al. found that with the introduction of electron-deficient pentafluorophenyl rings at the meso positions of the porphyrin scaffold, **Pt-2** exhibited superior stability against oxidative degradation relative to that of the parental complex [Pt(TPP)] (TPP = 5,10,15,20-tetraphenylporphyrinato) (**Figure 2**) [28]. Saturated red (λmax = 647 nm) porphyrin-centered phosphorescence with a long lifetime (τem = 60 μs) was observed for **Pt-2** in CH2Cl2 at room temperature. Saturated red OLED devices with different doping concentrations of **Pt-2** have

anaerobic conditions because the emissive excited state is essentially 3

can be rationally tuned by modifying the porphyrin ligands.

cent emitters has attracted considerable interest [25–27].

π-π\* electronic transitions. The triplet formation yields for

LC (3

π, π\* ) in

**166**

The data from devices prepared by spin coating these dendrimers as the non-doped emissive layer are better than those of small molecule Pt(II) porphyrin analogs.

The emission of platinum(II) porphyrin complexes can be further shifted to the NIR region by extending the π conjugation of the porphyrin ligand [30]. Schanze and co-workers developed a series of NIR-emitting platinum(II) di- and tetrasubstituted benzoporphyrin complexes, **Pt-6**–**8** (**Figure 2**), to investigate structureproperty relationships and the link between photophysical parameters and OLED performances. The photophysical parameters are listed in **Table 1**. Although the di-substituted porphyrin complex gives a higher ФPL (0.49) and longer τem (53.0 μs) than the tetra-substituted complexes (ФPL = 0.33–0.35; τem = 29.9–32.0 μs) in solution, the same trend does not hold in solid matrices, in which the emission lifetimes of **Pt-6**–**8** are comparable (45.7–57.5 μs). The EQEs of all the devices (8.0–9.2%) were similar. Consequently, the authors concluded that (i) the major non-radiative decays are associated with out-of-plane distortion of the porphyrin ligands, (ii) the rigid polymer matrix could help suppress the enhanced non-radiative decay of the more distorted complexes (**Pt-6** and **Pt-7**) in solid matrices, and (iii) the performance of platinum(II) benzoporphyrin-based OLEDs was observed to strongly correlate with the emission lifetime in the solid matrix.

Pt(II) porphyrins as OLED emitters generally exhibit high thermal stability and outstanding performance in saturated red and NIR devices in terms of color purity and EL efficiencies attributed to their narrow emission band and high emission quantum yields. Nevertheless, the practical interest of this class of Pt(II) emitters is limited by the long emission decay times, which would result in substantial efficiency loss at higher luminance. It is hypothesized that careful device design and the use of appropriate auxiliary materials to mitigate TTA, e.g., by using a double host to broaden the recombination zone, could be a strategy for improving the practicality of these materials.


**3. Conclusions and perspectives**

and P(P)4

be potentially synthesized.

146 Descriptive Inorganic Chemistry Researches of Metal Compounds

found on the Zn‐centres.

**Figure 4.** Structures of the [ZnP(P)4

]2

permission conveyed through Copyright Clearance Center, Inc.

2−/P2− were shown to be very similar for both ligands. The full P‐modification of the

species

units (**Figure 4**).

stacks, binding modes I (a), II (b), and III (c), calculated at the B3LYP/6‐31G\*

level of theory. Republished with permission of Journal of Theoretical and Computational Chemistry, Kuznetsov [66];

porphyrin core was found to decrease the Mn+‐ligand binding energies; however, the MP(P)4 compounds studied were shown to be stable according to the Ebind values and therefore can

Also in 2016, due to motivation by the phenomenon of formation of stacks by regular metal‐

without any linkers or substituents was performed [66]. Three modes of binding or coordina‐

The 'convexity‐to‐convexity' dimer I was found to be the most stable compound with the highest binding energy. In the dimer I, the strongly convex shape of both monomer units was demonstrated. The Zn–Zn distances in the dimer I, ca. 3.5 Å, were computed to be signifi‐ cantly shorter than in two other dimers. In the dimer I, significant decrease of the charge was

loporphyrins, the computational check of the stack formation between the MP(P)4

tion were found to be possible between the monomeric ZnP(P)4

Thus, as can be seen from this micro‐review, core modification of the porphyrins and their derivatives with other elements than N is a very promising and productive approach to modify and fine‐tune their structures, electronic and coordination properties and reactivities. The research in this area has already been quite productive and brought for our attention numerous compounds with unusual novel structures and properties, which makes these species great candidates for different fields in chemistry and nano‐ technology. Without any doubts, studies in this area will be continued and broadened. Based on the considered studies of porphyrin derivatives core‐modified by other ele‐ ments, we can summarize subareas (or research directions), which would be necessary to focus on to employ the core‐modified porphyrins for the design of building blocks for nanotechnology: