patients with schizophrenia ( scz ) exhibit a wide variety of cognitive deficits , particularly with memory ( barch and ceaser , 2012 ; ranganath et al . , 2008 ) .
these deficits are predictive of overall functional outcome and clinical remission ( bodnar et al . , 2008 ; green , 2006 ; green et al . , 2004 ; kahn and keefe , 2013 ) , and it has recently been suggested that schizophrenia should be viewed primarily as a cognitive disorder ( kahn and keefe , 2013 ) .
understanding the nature of the memory deficits is therefore a critical goal when moving towards improved clinical interventions in scz .
when considering episodic memory , one area in which patients with scz have a substantial deficit is with source monitoring ( identifying the context in which a stimulus was encountered ; johnson et al . , 1993 ) .
for successful source monitoring it is necessary to bind elements of a memory together into a memory trace , along with their context ( spatial context , temporal context , etc . ) .
patients demonstrate source monitoring deficits even when stimulus recognition is preserved ( danion et al . , 1999 ;
this deficit in source monitoring is in many ways not surprising given that patients with scz also demonstrate difficulties with relational or associative memory ( binding items together during memory encoding , and later recalling which stimuli were presented together ) , while object memory is not as severely impaired ( achim et al .
most typically , source monitoring problems in scz are considered in the context of attributing events from internal ( self ) to external sources .
patients with predominant hallucinations and thought disorder have a greater tendency or bias to attribute internally generated events to an external source , while still being able to correctly identify externally generated stimuli ( brunelin et al .
this bias for scz to misattribute internal sources has been observed in the absence of recognition memory deficits or false positive responses ( fisher et al . , 2008 ) .
interestingly , in a repetitive magnetic stimulation trial of low frequency ( 1  hz , inhibitory ) stimulation to the left temporal parietal junction over 5 consecutive days not only improved auditory hallucinations but also resulted in an improvement in source monitoring compared to sham stimulation ( brunelin et al . , 2006 ) .
the improvement in auditory hallucination was marginally correlated with the improvement in source monitoring , further suggesting the relationship between source monitoring and hallucinations .
patients with schizophrenia have also been found to have a deficit in source memory ( remembering the context in which experimental stimuli occurred ; brebion et al . , 2002 ;
the deficit in source memory has been related to deficits in binding contextual cues together into a holistic memory representation ( diaz - asper et al . , 2008 ; waters et al . , 2004 ) , which is an essential component of source memory .
source memory errors are present in scz even for short - term recognition ( when source information is tested immediately , minimizing the need to recollect information stored in long - term memory ) , suggesting that source memory deficits in scz may be related to encoding errors rather than problems in recognition ( achim et al . , 2011 ) .
( 2009 ) performed a list learning task in scz and found that patients who hallucinate had more intrusions ( indicating a word was part of the memory set when it was not ) than non - hallucinating patients .
this finding was related to source misattribution ( patients attributing an internally generated stimulus to an external source , the original memory set ) .
overall , scz appears to have a noteworthy deficit in source memory which is likely intricately related to other memory and cognitive processes , such as contextual binding and episodic memory . within healthy controls ,
source memory involves a range of cortical regions known to be involved in episodic memory , including the medial temporal lobes , prefrontal cortex , and parietal cortex . increased hippocampal activity has been related to trials in which the source was correctly identified ( davachi et al . , 2003 ; ranganath et al . ,
2004 ) , probably due to the role of the hippocampus in relational binding ( davachi , 2006 ) .
one of the first fmri studies to examine source memory found greater left prefrontal activity for source memory and for old  new recognition ( nolde et al . , 1998 ) , with subsequent studies finding activity in the left lateral prefrontal cortex associated with source memory for a variety of stimuli types ( mitchell and johnson , 2009 ) .
prefrontal lesions have been found to disrupt the self - initiation of processes which promote feature binding ( stuss and benson , 1986 ) , and left prefrontal damage is associated with deficits in source monitoring ( duarte et al . , 2005 ) .
prefrontal activity during source recognition may be more involved in the evaluation of source information ( e.g.  does this stimuli fit with source x  ) rather than retrieving source information per se ( mitchell et al . ,
activity in medial parietal areas ( intraparietal sulcus and precuneus ) has been suggested to be present regardless of the type of source information being assessed ( uncapher et al . , 2006 ) , while activity in lateral parietal areas may be more dependent on how well the information has been encoded ( wheeler and buckner , 2004 ) and/or to attentional processes ( cabeza , 2008 ) . examining declines in source memory with age
has proven fruitful for examining structural and functional correlates of source memory , with evidence that age - related decline in source memory is related to decreased activity mainly in the prefrontal and medial temporal lobes ( see mitchell and johnson , 2009 , for review ) .
( 2006 ) examined source monitoring in scz using a level - of - processing framework .
patients were presented words with either deep ( semantic ) or shallow ( orthographic ) encoding instructions . during recognition , when participants successfully identified a previously encountered stimuli they were asked under which encoding condition the word was encountered ( the source memory aspect being recalling the context in which the word was encountered , in this case , which encoding condition ) . when contrasting correct vs. incorrect source , both patients and controls activated areas of prefrontal and parietal cortices .
patients showed activity in the middle and superior temporal gyrus , thalamus , and parahippocampal gyrus , which was correlated with more severe positive and negative symptoms independent of memory performance .
other neuroimaging studies of source monitoring in scz have focused on deficits related to attributing stimuli as self - generated or externally - generated ( reality monitoring ) .
deficits in reality monitoring appear to involve the medial prefrontal cortex ( subramaniam et al . , 2012 ; vinogradov et al . , 2008 ; wang et al . , 2011 ) . following computerized training to improve source monitoring ,
activity was found to be increased in the medial prefrontal cortex ( subramaniam et al . , 2012 ) .
the purpose of this study was to examine the neural correlates of source memory in schizophrenia . while most previous studies of source memory ( in both controls and schizophrenia ) have used less ecologically valid task ( e.g. identifying the color of the stimuli during encoding ) , we utilized a paradigm involving encounters ( with a person and an object in a specific place ) within a realistic 3d environment ( burgess et al . , 2001 ; king et al . , 2005 ) , which may better evaluate source memory networks used in everyday life .
we examined participants with early schizophrenia ( within the first 4.5  years of treatment , with 75% of patients within the first 2  years ) thus minimizing potential confounds associated with prolonged illness such as cognitive decline , social isolation and long - term medication effects . during
fmri scanning a source recognition memory task was employed , which was contrasted with an object memory task . by directly comparing source memory to object memory
, we can identify regions in the cortex which are specific to source memory compared to object memory and determine if any deficits observed in schizophrenia are source - memory specific .
we hypothesized that patients would show deficits in source memory relative to object memory and may show compensatory activation in source memory retrieval contrasts .
furthermore , as deficits in source memory have been associated with auditory hallucinations ( woodward et al . , 2007 )
we expected to observe relationships between hallucinations and the neural activity of source memory retrieval .
all participants with scz were treated at the douglas mental health university institute in montreal , canada , at the prevention and early intervention program for psychoses , a specialized service providing treatment to individuals aged 1435  years from a local catchment area .
individuals with an iq  >  70 who had not taken antipsychotic medication for more than 1  month were consecutively admitted as in- or out - patients .
patients were assessed with the scale for assessment of positive symptoms ( saps ) ( andreasen , 1984 ) and the scale for assessment of negative symptoms ( sans ) ( andreasen , 1983 ) at numerous time - points following clinic admission ( baseline ; at 1 , 2 , 3 , 6 , 9 , and 12  months ; and every 6  months thereafter ) .
( 2003 ) or visit http://www.douglas.qc.ca/pages/view?section_id=165 for more details . for the neuroimaging study , only individuals aged 1830  years with no previous history of neurological disease , head trauma causing loss of consciousness , or lifetime diagnosis of substance dependence
twenty - five people with schizophrenia spectrum disorders were recruited , diagnosed according to the structured clinical interview for dsm - iv ( first et al . , 1997 ) and confirmed between two senior research psychiatrists ( a.m. and r.j . ) .
twenty - four healthy controls were recruited through advertisements in local newspapers and were included only if they had no current or previous history of any axis i disorders , neurological diseases , or head trauma causing loss of consciousness , and no first - degree family members with schizophrenia or related schizophrenia - spectrum disorders .
all patients provided written informed consent , and the study was approved by the research ethics boards of the douglas hospital research centre and the montreal neurological institute .
participants performed an encoding task ( outside the mri ) using a modified version of the virtual city developed by burgess and colleagues ( burgess et al .
, 2001 ; king et al . , 2005 ) , created using 3ds max ( 3ds max , 2011 ) and unity software ( unity , 2011 ) .
participants navigated through a 3d virtual city , following a path indicated by green arrows to the site of an encounter ( an encoding trial , a character at a location ) . after approaching within five virtual meters of the character , the participant 's view was frozen and the character stepped aside , and a life - sized object appeared on a small table displayed to the right .
participants were instructed to pay careful attention to the object , character and location , and try to remember for a later memory test .
after a 5  s study delay the person and object disappeared , and participants then followed the arrows to the next encounter .
there were a total of 20 encounters , each with a unique person , location and object .
a total of 80 recognition trials were administered , in which participants were shown an image consisting of a typical viewpoint encountered within the virtual city ( in one of 20 places where encounters occurred ) , with a person in the center of the screen , and two objects , one on each side of the person .
participants were then asked one of four possible recognition questions : ( 1 ) person ( which object was paired with this person ) , ( 2 ) place ( which object did you view in this location ) , ( 3 ) object ( which object was viewed in the city ; the other object was new ) , and ( 4 ) bright ( which object is brighter in appearance ) .
participants responded on an mri - compatible button box to indicate which item ( left or right ) was selected .
for the person condition , the place was not associated with either object , while in the place condition the person was not associated with either object .
the person and place conditions were designed to access source memory ( in what context was an object encountered ) while the object condition assesses object memory ( old vs. new ) .
including two source memory conditions allows us to better understand if the observed activity is modality specific .
the bright condition was not considered in this analysis as we were specifically interested in source vs. object memory .
images ( with encoding question ) were presented on the screen for 8000  ms , with a 20008000  ms isi ( in 100  ms increments ) , with an average trial length of 13  s. stimuli were presented and results were recorded through e - prime 1.0 software .
1 . a practice route was designed to allow participants to become familiar with the arrow key and mouse , and to practice following the arrows and encounter two characters with objects in independent locales .
participants also practiced answering two of each of the four forced - choice recognition questions regarding the objects collected .
echo - planar images were collected on a siemens 3  t tim trio mri ( tr  =  2000  ms , te  =  30  ms , flip angle  =  90 , 36 slices of 4  mm thick , 64    64  voxel plane with an fov of 256  mm 4  mm slices ) .
each bold run was preceded by 4 volumes that were later discarded to allow a magnetic steady state .
the anatomical scan was an mprage ( tr  =  2300  ms , te  =  2.98  ms , fov 256 , 1    1    1  mm  voxels , flip angle  =  9 ) and lasted 5.21  min .
data analysis was conducted using spm 8 ( wellcome department of cognitive neurology , london , uk ) .
data was motion corrected by realigning to the 3rd tr , normalized to the icbm template ( and resampled at 2    2    2  mm  voxel size ) and smoothed with an 8  mm isotropic gaussian kernel . the general linear model was implemented by convolving a standard hemodynamic response function and its first temporal derivative and dispersion .
events were defined based upon recognition question ( person , place , object , or bright ) , with incorrect answers modeled as distinct event types and excluded from further analysis .
accuracy data was not available for three controls and four scz patients due to technical problems during initial data collection . for these participants ,
contrasts were person vs. object and place vs. object ( both performed bidirectionally ) to identify voxels which are differentially activated by source or object memory .
a second level analysis was performed separately for each group ( controls or scz ) using a one sample t - test .
corrections for multiple comparisons were performed at the cluster level using an individual voxel threshold of p  <  0.001 ( uncorrected ) . a monte - carlo simulation of 1000 iterations ( slotnick et al
. , 2003 ) resulted in a cluster extent threshold of 49 resampled voxels . to test for differences between groups ,
an independent - samples t - test was performed , using the contrast  value derived for each participant from the above contrasts .
given that between - group differences often have smaller effect sizes , we used a slightly more liberal single - voxel threshold of p  <  0.005 , but corrected to p  <  0.01 at the cluster level ( resulting in an extent threshold of 97  voxels ) . a regression analysis in patients was performed to examine the relationship between source memory and clinical symptoms .
as patients were stabilized and undergoing treatment at the time of scanning , few patients were actively experiencing positive symptoms as of the assessment closest to the date of scanning . as a result
, the data did not possess sufficient variability for a regression analysis ( the majority of cases had global scores of 0 or 1 on the saps at closest assessment ) .
furthermore , positive symptoms are often highly responsive to treatment ( malla et al . , 2006 ; robinson et al .
, 1999 ) . as such any patient displaying continued positive symptoms may represent treatment resistant patients or those with a more severe illness , rather than relate to the symptoms themselves per se .
instead , we utilized scores from the assessment at the initial visit to the clinic , prior to treatment onset .
the presence of specific symptoms at initial clinical assessment was considered as a proxy of how prone to those symptoms each patient may be .
we propose that the pre - treatment ratings best represent the underlying neurobiology and clinical characteristics of individual patients , as they show their symptom characteristics in an untreated state of illness .
while it is not possible to make several such assessments prior to treatment onset ( which would best capture the potential symptom profile of each patient ) , such an approach may allow for a data exploration which separates patients who are prone to certain symptoms ( such as hallucinations ) from those who have experienced less or never experienced those symptoms while in an untreated state .
as such , this can be conceptualized as a  trait based approach to symptom evaluation . saps scores for global hallucinations and global thought disorder were entered into a whole - brain regression model with the person  >  object and place  >  object contrasts . the global delusion score was not included as most patients were highly delusional at baseline . in order to account for differences in time since initial diagnosis ,
the interval between baseline assessment and mri scan ( in days ) was entered as a covariate in the second - level regression analysis .
cluster threshold for the regression was 49  voxels at p  <  0.001 uncorrected ( voxel threshold ) .
there were no significant differences in age or gender distribution between groups , though patients had a marginally significant lower parental ses and significantly fewer years of education .
accuracy in the person , place and object conditions was assessed using independent samples t - test .
schizophrenia patients had significantly lower accuracy in the person condition , t(40 )  =  2.247 , p  =  0.03 , but not for place , t(40 )  =  0.44 , p  =  0.66 , or object , t(40 )  =  0.07 , p  =  0.95 .
numerous cortical regions showed significant increases in neural activity for retrieval of source memory over retrieval of object memory , similar to the pattern observed in previous studies using a similar paradigm ( burgess et al .
, 2001 ; king et al . , 2005 ) . activated regions in the source memory contrasts ( person  >  object and place  >  object ) included bilateral activity around the parietal occipital sulcus ( including the precuneus and retrosplenial cortex ) extending into the superior parietal cortex , left inferior frontal gyrus ( vlpfc ) , fusiform gyrus bilaterally , and the occipital cortex .
activity in the person  >  object contrast included the head of the caudate nucleus , the right inferior frontal ( vlpfc ) , and the medial aspect of the superior frontal gyrus .
object  >  place showed widespread activity in the medial frontal cortex and parietal cortices ( supramarginal gyrus bilaterally ) and smaller clusters in the frontal and occipital cortices .
for the object  >  person contrast , activity was observed in the left and right angular gyrus .
2 . when examining source vs. object retrieval contrasts in scz , a smaller number of significantly activated voxels were observed relative to the activity maps of controls . in the person 
>  object contrast only smaller clusters in the head of the caudate and occipital cortex were significant .
in place  >  object , mainly posterior activity was observed ( e.g. parietal occipital sulcus and fusiform cortex ) . in both
the object  >  person and object  >  place , scz showed a right inferior frontal ( vlpfc ) activity which was not observed in controls .
2 . when comparing between groups , controls demonstrated regions of greater differences between conditions than scz for person  >  object condition ( including bilaterally in the precuneus and superior parietal , and left and right inferior frontal in the vlpfc ) and for place  >  object ( bilaterally in the superior parietal , and the left precuneus ) .
schizophrenia patients had greater differences between conditions than controls when considering place  >  object across a wide range of areas .
the group comparison was run using contrast  values , which can be positive ( e.g. if place  >  object ) or negative ( e.g. if object  >  place ) .
thus , while we observed greater activity in scz than control in the place  >  object contrast , it is not clear from the activation maps if such a difference is due to changes in activity in either object or place . in order to visualize the results for each condition ,
beta values were extracted for an roi of 11  voxels ( 9 in - plane voxels surrounding the selected voxel and one above and one below ) .
rois were selected to represent a range of representative patterns of activity across the brain ( e.g. regions in which controls showed differences from scz in both person  >  object and place  >  object , and regions in which scz showed  greater  activity in place  >  object ) .
which controls had greater differences between conditions than scz , controls are showing increased activity to the source memory conditions ( person and/or place ) relative to object , while  values in scz do not show any such differentiation .
interestingly , in regions in which we observed  greater  differences between conditions ( in this case , place  >  object ) in scz than controls , we again observe little differences between source memory and object memory in scz .
thus , it is not that patients with scz are showing greater activity in the place condition , but that they are failing to modulate brain activity in the same way as control participants .
results of the regression analysis with positive symptoms are presented in table 6 and fig .
we observed significant negative correlations with the global hallucination score from the saps ( at first assessment ) and place  >  object contrast , in the right midtemporal gyrus , left prefrontal cortex , and right cerebellum ( in a region noted in at least one lesional case study to be associated with source memory deficits ; tamagni et al . ,
2010 ) . in order to examine the relationship between recognition memory performance and neural activity , spearman 's correlations were run on global hallucination score , memory performance in the place and object conditions , and  values from the three clusters .
while hallucinations did not significantly correlate with performance in either condition ( place , rho  =  .228 , p  =  0.32 ; object , rho  =  0.28 , p  =  0.22 ) , there was a marginally significant correlation between performance in the object condition and  value in the dlpfc cluster ( rho  =  0.38 , p  =  0.088 ) .
this study examined differences in the neural correlates of source memory in patients with schizophrenia and controls .
we examined this issue using a virtual reality paradigm , which has improved ecological validity when assessing the  source  of a memory , as compared to other studies which have used less ecologically valid tasks .
furthermore , we examined a group of patients , who were within the first 4.5  years of treatment avoiding potential issues associated with illness chronicity such as cognitive decline , prolonged exposure to medications ( although medication exposure remains an issue ) , social isolation , and sedentary lifestyle ( pelletier et al . , 2005 ) . while patients with scz demonstrated some activation in the source memory contrasts , the extent and magnitude of activity were substantially less than those in controls . even in regions in which the difference appeared to be in the directions of scz  >  controls
, it seems to be the case that controls differentiate between source and object memory while patients do not .
as discussed below , this finding may be true of other forms of memory , and may therefore be representative of the underlying deficit across a range of memory subtypes .
more specifically , patients with scz may fail to activate cortical regions which facilitate elaborative memory processes .
this is consistent with previous findings of relatively intact object memory in scz ( achim et al .
2009 ) , but deficits in source memory ( johnson et al . , 1993 ) and associative memory ( achim and lepage , 2003 ) .
it may be that the vr environment minimizes these behavioral differences , in that the place condition may be easier than person as locations were more distinct from each other relative to the 3d rendered characters .
alternatively , our recent - onset sample may have better preserved function than the more enduring schizophrenia samples often examined . however , this lack of behavioral difference has a positive aspect , in that it removes performance as a potentially major confound in the fmri analysis . had patients with schizophrenia demonstrated profound deficits in performance , it would beg the question if any observed neural activity differences were due to disease pathology or simply related to poor performance ( and as such would be similar to poor performing healthy controls ) .
we did observe a performance difference in the person condition , and interestingly very little significant activity in the schizophrenia group for person  >  object .
however , some activations observed in the group analysis , particularly in the posterior regions , were present in both person  >  object and place  >  object , suggesting that these differences were not at all modality specific .
negative correlations were observed between the difference in neural activity in place  >  object and global hallucinations , measured at intake baseline using the saps .
this suggests that the propensity of an individual to experience hallucination may modulate differences between source and object memory in these areas .
we did not observe significant correlations with global thought disorder , which is not surprising as hallucinations but not thought disorder are generally associated with source memory ( woodward et al . , 2007 ) .
while these regions did not directly overlap activity observed in the healthy control group , the left frontal cluster was proximal to significant activity in place  >  object in controls , while the middle - temporal cluster was proximal to significant voxels in the object  >  place clusters in controls , suggesting that these regions are at least similar to those observed in healthy controls .
however , the lack of direct overlap and given the nature of the result ( greater difference with more hallucinations ) , it is possible that these regions represent malfunctioning cortical regions which are more active in patients who have experienced hallucinations as part of their disorder .
this over - activation within these regions when considering source information may play an important role in generating hallucinations , which are essentially the misattribution of internally generated stimuli to an external source .
at least one study has found relationships between the left prefrontal cortex and the right temporal cortex while patients are actively experiencing hallucinations ( hoffman et al . , 2011 ) , and
a meta - analysis suggests that these regions among others are frequently active during hallucination ( jardri et al . , 2011 ) . as such , the regions found to be significantly active in our regression are consistent with the existing literature on the neurobiology of hallucinations .
while many studies examining hallucinations have utilized either general  state based measurements ( approximately how much the participant is hallucinating in general at the time ) or direct analysis of overall activity during hallucinations , we have attempted to utilize a 
our sample of patients early in treatment makes such an approach possible with minimal confounding for chronicity ( which we attempted to control for by including length of treatment as a covariate in the regression ) .
our results overall suggest a relationship between mal - adaptive neural activity related to source memory retrieval and how prone participants are to hallucinatory symptoms , further verifying the relationship between source memory and hallucinations ( woodward et al . , 2007 ) . however , some limitations must be considered as well .
while we have attempted to use baseline scores as a  trait measure of how prone an individual is to hallucinations , it is well known that clinical symptoms can vary across time . as such , the appropriate method for evaluating 
trait symptoms is to take repeated symptom measurements over time ( mathalon and ford , 2012 ) .
it would be preferable to have several assessments of pre - treatment symptoms to have a complete picture of the symptom profile of a given patient , but this is not possible as it would require delaying treatment . as such we utilized the best available measure to assess pre - treatment symptom profile , which produced results which are consistent with the existing literature on those symptoms .
however , it is important to remain considerate of the limitations of our measures when considering these results .
source memory can be considered a form of associative / relational memory , as participants are binding elements together during encoding and storing these elements together as part of a larger whole .
a deficit in source memory can be viewed as a failure to associate a memory item with its context . in the case of this study in particular ,
our source memory paradigm is not far removed from studies examining associative memory ( achim et al . , 2007 ; achim and lepage , 2005 ; murray and ranganath , 2007 ) , which is known to be more impaired in scz than object memory ( achim and lepage , 2003 ) .
some studies have suggested that patients with schizophrenia do not properly differentiate between associative and item memory ( achim et al .
2012 ) , in keeping with suggestions that source memory impairments are part of associative memory impairments ( achim et al . , 2011 ) .
our present study focused on source retrieval , and as such we can not definitively determine if the differences observed in our contrasts are driven by deficits in encoding ( in that the information was not properly moved into memory ) or retrieval ( in that the memories may have been encoded but are not properly accessed ) , or a combination of both ( which seems likely given the plurality of evidence for memory deficits in scz ) .
( 2011 ) found deficits in source memory even when using short term recall , minimizing the need for retrieval of information from long - term memory .
this suggests that at least part of the source memory deficit in scz is related to problems with encoding .
our finding of an overall pattern of lack of differentiation between conditions may be a fairly consistent finding in the cognitive neuroscience of memory in scz , regardless if one considers activity during encoding or retrieval / recognition .
core regions required for task performance may be relativity intact in scz , while deficits in activity will be observed in 
that is to say , the deficits in memory ( and possibly cognition in general ) are related to a lack of engagement of extended cortical regions .
these extended regions are not critically required for minimal task performance , but instead serve to enhance performance ( such as regions involved in cognitive control processes ) .
healthy controls will tend to utilize such areas automatically , while patients with schizophrenia will fail to do so .
for example , patients with scz have been shown to have impairments in initiating elaborative encoding processes which may be beneficial during associative encoding ( brebion et al .
however , when patients are specifically instructed to utilize effective encoding strategies they show an improvement in memory performance , demonstrating that patients with scz can utilize such encoding strategies when specifically instructed but fail to do so spontaneously ( brebion et al . , 1997 ) .
this pattern of results is similar to that in patients with prefrontal cortical lesions ( alexander et al . , 2003 ) .
bonner - jackson et al . ( 2008 ) examined memory strategies in schizophrenia by contrasting intentional but unstructured encoding ( simply instructing participant to memorize words ) with an externally imposed deep encoding strategy ( having participants perform an abstract / concrete judgement on words , deep semantic encoding which facilitates memory encoding ; craik and lockhart , 1972 ) .
they observed group    encoding interactions in several regions , including the left inferior frontal gyrus and precuneus , with the most common finding being a difference between controls and scz in the incidental , unstructured encoding condition .
for example , in the left inferior frontal cortex , scz patients showed no activity for unstructured encoding , but substantial activity for deep encoding .
that is to say , when scz patients were provided a structured encoding strategy they activated this region , but failed to do so spontaneously .
likewise , controls showed significantly better memory performance than scz patients for the deep encoding condition .
further support for the importance in strategic and/or cognitive control comes from findings of changes and/or normalization of activity in scz following cognitive training ( hooker et al . , 2012 ; penades et al . ,
within both encoding and recognition studies in schizophrenia , the most prevalent finding is a decrease in the extent or magnitude of activity in scz patients relative to controls , although many studies also report findings in the direction of scz  >  controls ( ragland et al . , 2009 ) .
while it is likely that scz often shows compensatory networks or inefficient over - activation during cognitive tasks , it can be difficult to judge from many of the published studies on cognition in scz .
many papers report differences in group activities without also reporting the parameter estimates which accompany those changes .
if we had done so in this study ( by only presenting the activation maps in fig .
3 and not the beta values ) we may have concluded that scz showed greater activity in some regions for place vs. object and concluded that this was compensatory of maladaptive over - activation . however , when examining the beta values , we realize that this is not the case but instead these are regions where controls show greater activity for object over place ( often in the form of a decrease in activity for place ) .
this highlights the importance of carefully examining parameter estimates when performing between - group comparisons .
it is possible that in at least some cases in the existing literature , the so - called 
compensatory activity may instead be a lack of activity relative to the control group , such as was the case in this study .
such ambiguity and misinterpretation can be avoided if studies fully report parameter estimates for contrasts which differ between groups .
we have reported the results of a study looking at source memory retrieval in scz using a virtual reality environment on a group of patients relatively early into treatment .
while controls activated a large , extensive network for source relative to object retrieval , scz showed a marked reduction in activity .
this reduction was borne out in the group comparison , and appears to be related to the fact that patients with scz are failing to activate these regions or differentiate between object and source retrieval . despite the large - scale group differences , patients were still able to perform the source retrieval tasks , suggesting that at least some of the  core system involved in source retrieval is intact . instead , we propose that the observed differences are related to  supporting regions which are not critical to task performance but instead facilitate source retrieval .
that is , patients may generally fail to engage extended cortical networks which facilitate task performance and facilitate overall cognitive functioning .
 source memory , the ability to identify the context in which a memory occurred , is impaired in schizophrenia and has been related to clinical symptoms such as hallucinations . 
 the neurobiological underpinnings of this deficit are not well understood . 
 twenty - five patients with recent onset schizophrenia ( within the first 4.5  years of treatment ) and twenty - four healthy controls completed a source memory task . 
 participants navigated through a 3d virtual city , and had 20 encounters of an object with a person at a place . 
 functional magnetic resonance imaging was performed during a subsequent forced - choice recognition test . 
 two objects were presented and participants were asked to either identify which object was seen ( new vs. old object recognition ) , or identify which of the two old objects was associated with either the person or the place being presented ( source memory recognition ) . source memory was examined by contrasting person or place with object . 
 both patients and controls demonstrated significant neural activity to source memory relative to object memory , though activity in controls was much more widespread . 
 group differences were observed in several regions , including the medial parietal and cingulate cortex , lateral frontal lobes and right superior temporal gyrus . 
 patients with schizophrenia did not differentiate between source and object memory in these regions . 
 positive correlations with hallucination proneness were observed in the left frontal and right middle temporal cortices and cerebellum . 
 patients with schizophrenia have a deficit in the neural circuits which facilitate source memory , which may underlie both the deficits in this domain and be related to auditory hallucinations . 
Introduction
Methods
Results
Discussion
Conclusions