of motor control and perception. part b of the trail-making test consists of multiple circles containing letters (a-l) and numbers (1-12). the participant's objective for this test is to connect the circles in order, alternating between number and letter (e.g. 1-a-2-b) from start to finish. the participant is required not to lift their pencil from the page. the task is also timed as a means of assessing speed of processing. set-switching tasks in part b have low motor and perceptual selection demands, and therefore provide a clearer index of executive function. throughout this task, some of the executive function skills that are being measured include impulsivity, visual attention and motor speed. in clinical populations the executive system's broad range of functions relies on, and is instrumental in, a broad range of neurocognitive processes. clinical presentation of severe executive dysfunction that is unrelated to a specific disease or disorder is classified as a dysexecutive syndrome, and often appears following damage to the frontal lobes of the cerebral cortex. as a result, executive dysfunction is implicated etiologically and/or co-morbidly in many psychiatric illnesses, which often show the same symptoms as the dysexecutive syndrome. it has been assessed and researched extensively in relation to cognitive developmental disorders, psychotic disorders, affective disorders, and conduct disorders, as well as neurodegenerative diseases and acquired brain injury (abi). environmental dependency syndrome is a dysexecutive syndrome marked by significant behavioural dependence on environmental cues and is marked by excessive imitation and utilization behaviour. it has been observed in patients with a variety of etiologies including abi, exposure to phendimetrazine tartrate, stroke, and various frontal lobe lesions. schizophrenia schizophrenia is commonly described as a mental disorder in which a person becomes detached from reality because of disruptions in the pattern of thinking and perception. although the etiology is not completely understood, it is closely related to dopaminergic activity and is strongly associated with both neurocognitive and genetic elements of executive dysfunction. individuals with schizophrenia may demonstrate amnesia for portions of their episodic memory. observed damage to explicit, consciously accessed, memory is generally attributed to the fragmented thoughts that characterize the disorder. these fragmented thoughts are suggested to produce a similarly fragmented organization in memory during encoding and storage, making retrieval more difficult. however, implicit memory is generally preserved in patients with schizophrenia. patients with schizophrenia demonstrate spared performance on measures of visual and verbal attention and concentration, as well as on immediate digit span recall, suggesting that observed deficits cannot be attributed to deficits in attention or short-term memory. however, impaired performance was measured on psychometric measures assumed to assess higher order executive function. working memory and multi-tasking impairments typically characterize the disorder. persons with schizophrenia also tend to demonstrate deficits in response inhibition and cognitive flexibility. patients often demonstrate noticeable deficits in the central executive component of working memory as conceptualized by baddeley and hitch. however, performance on tasks associated with the phonological loop and visuospatial sketchpad are typically less affected. more specifically, patients with schizophrenia show impairment to the central executive component of working memory, specific to tasks in which the visuospatial system is required for central executive control. the phonological system appears to be more generally spared overall. attention deficit hyperactivity disorder a triad of core symptoms – inattention, hyperactivity, and impulsivity – characterize attention deficit hyperactivity disorder (adhd). individuals with adhd often experience problems with organization, discipline, and setting priorities, and these difficulties often persist from childhood through adulthood. in both children and adults with adhd, an underlying executive dysfunction involving the prefrontal regions and other interconnected subcortical structures has been found. as a result, people with adhd commonly perform more poorly than matched controls on interference control, mental flexibility and verbal fluency. also, a more central impairment in self-regulation is noted in cases of adhd. however, some research has suggested the possibility that the severity of executive dysfunction in individuals with adhd declines with age as they learn to compensate for the aforementioned deficits. thus, a decrease in executive dysfunction in adults with adhd as compared to children with adhd is thought reflective of compensatory strategies employed on behalf of the adults (e.g. using schedules to organize tasks) rather than neurological differences. although adhd has typically been conceptualized in a categorical diagnostic paradigm, it has also been proposed that this disorder should be considered within a more dimensional behavioural model that links executive functions to observed deficits. proponents argue that classic conceptions of adhd falsely localize the problem at perception (input) rather than focusing on the inner processes involved in producing appropriate behaviour (output). moreover, others have theorized that the appropriate development of inhibition (something that is seen to be lacking in individuals with adhd) is essential for the normal performance of other neuropsychological abilities such as working memory, and emotional self-regulation. thus, within this model, deficits in inhibition are conceptualized to be developmental and the result of atypically operating executive systems. autism spectrum disorder autism is diagnosed based on the presence of markedly abnormal or impaired development in social interaction and communication and a markedly restricted or repetitive repertoire of stereotypic movements, activities, and/or interests. it is a disorder that is defined according to behaviour as no specific biological markers are known. due to the variability in severity and impairment in functioning exhibited by autistic people, the disorder is typically conceptualized as existing along a continuum (or spectrum) of severity. autistic individuals commonly show impairment in three main areas of executive functioning: fluency. fluency refers to the ability to generate novel ideas and responses. although adult populations are largely underrepresented in this area of research, findings have suggested that autistic children generate fewer novel words and ideas and produce less complex responses than matched controls. planning. planning refers to a complex, dynamic process, wherein a sequence of planned actions must be developed, monitored, re-evaluated and updated. autistic persons demonstrate impairment on tasks requiring planning abilities relative to typically functioning controls, with this impairment maintained over time. as might be suspected, in the case of autism comorbid with learning disability, an additive deficit is observed in many cases. flexibility. poor mental flexibility, as demonstrated in autistic individuals, is characterized by perseverative, stereotyped behaviour, and deficits in both the regulation and modulation of motor acts. some research has suggested that autistic individuals experience a sort of 'stuck-in-set' perseveration that is specific to the disorder, rather than a more global perseveration tendency. these deficits have been exhibited in cross-cultural samples and have been shown to persist over time. autistic individuals have also been shown to react slower as well as perform slower in tasks that require mental flexibility when compared to their neurotypical peers. although there has been some debate, inhibition is generally no longer considered to be an executive function deficit in autistic people. autistic individuals have demonstrated differential performance on various tests of inhibition, with results being taken to indicate a general difficulty in the inhibition of a habitual response. however, performance on the stroop task, for example, has been unimpaired relative to matched controls. an alternative explanation has suggested that executive function tests that demonstrate a clear rationale are passed by autistic individuals. in this light, it is the design of the measures of inhibition that have been implicated in the observation of impaired performance rather than inhibition being a core deficit. in general, autistic individuals show relatively spared performance on tasks that do not require mentalization. these include: use of desire and emotion words, sequencing behavioural pictures, and the recognition of basic facial emotional expressions. in contrast, autistic individuals typically demonstrated impaired performance on tasks that do require mentalizing. these include: false beliefs, use of belief and idea words, sequencing mentalistic pictures, and recognizing complex emotions such as admiring or scheming. bipolar disorder bipolar disorder is a mood disorder that is characterized by both highs (mania) and lows (depression) in mood. these changes in mood sometimes alternate rapidly (changes within days or weeks) and sometimes not so rapidly (within weeks or months). current research provides strong evidence of cognitive impairments in individuals with bipolar disorder, particularly in executive function and verbal learning. moreover, these cognitive deficits appear to be consistent cross-culturally, indicating that these impairments are characteristic of the disorder and not attributable to differences in cultural values, norms, or practice. functional neuroimaging studies have implicated abnormalities in the dorsolateral prefrontal cortex and the anterior cingulate cortex as being volumetrically different in individuals with bipolar disorder. individuals affected by bipolar disorder exhibit deficits in strategic thinking, inhibitory control, working memory, attention, and initiation that are independent of affective state. in contrast to the more generalized cognitive impairment demonstrated in persons with schizophrenia, for example, deficits in bipolar disorder are typically less severe and more restricted. it has been suggested that a "stable dys-regulation of prefrontal function or the subcortical-frontal circuitry may underlie the cognitive disturbances of bipolar disorder". executive dysfunction in bipolar disorder is suggested to be associated particularly with the manic state, and is largely accounted for in terms of the formal thought disorder that is a feature of mania. it is important to note, however, that patients with bipolar disorder with a history of psychosis demonstrated greater impairment on measures of executive functioning and spatial working memory compared with bipolar patients without a history of psychosis suggesting that psychotic symptoms are correlated with executive dysfunction. parkinson's disease parkinson's disease (pd) primarily involves damage to subcortical brain structures and is usually associated with movement difficulties, in addition to problems with memory and thought processes. persons affected by pd often demonstrate difficulties in working memory, a component of executive functioning. cognitive deficits found in early pd process appear to involve primarily the fronto-executive functions. moreover, studies of the role of dopamine in the cognition of pd patients have suggested that pd patients with inadequate dopamine supplementation are more impaired in their performance on measures of executive functioning. this suggests that dopamine may contribute to executive control processes. increased distractibility, problems in set formation and maintaining and shifting attentional sets, deficits in executive functions such as self-directed planning, problems solving, and working memory have been reported in pd patients. in terms of working memory specifically, persons with pd show deficits in the areas of: a) spatial working memory; b) central executive aspects of working memory; c) loss of episodic memories; d) locating events in time. spatial working memorypd patients often demonstrate difficulty in updating changes in spatial information and often become disoriented. they do not keep track of spatial contextual information in the same way that a typical person would do almost automatically. similarly, they often have trouble remembering the locations of objects that they have recently seen, and thus also have trouble with encoding this information into long-term memory. central executive aspectspd is often characterized by a difficulty in regulating and controlling one's stream of thought, and how memories are utilized in guiding future behaviour. also, persons affected by pd often demonstrate perseverative behaviours such as continuing to pursue a goal after it is completed, or an inability to adopt a new strategy that may be more appropriate in achieving a goal. however, some research from 2007 suggests that pd patients may actually be less persistent in pursuing goals than typical persons and may abandon tasks sooner when they encounter problems of a higher level of difficulty. loss of episodic memoriesthe loss of episodic memories in pd patients typically demonstrates a temporal gradient wherein older memories are generally more preserved than newer memories. also, while forgetting event content is less compromised in parkinson's than in alzheimer's, the opposite is true for event data memories. locating events in timepd patients often demonstrate deficits in their ability to sequence information, or date events. part of the problems is hypothesized to be due to a more fundamental difficulty in coordinating or planning retrieval strategies, rather than failure at the level of encoding or storing information in memory. this deficit is also likely to be due to an underlying difficulty in properly retrieving script information. pd patients often exhibit signs of irrelevant intrusions, incorrect ordering of events, and omission of minor components in their script retrieval, leading to disorganized and inappropriate application of script information. psychosocial treatment since 1997, there has been experimental and clinical practice of psychosocial treatment for adults with executive dysfunction,