Selective attention in schizophrenia: relationship to verbal working memory

Knockdown of Lhx6 during embryonic development results in neurophysiological alterations and behavioral deficits analogous to schizophrenia in adult rats

A decreased expression of specific interneuron subtypes, containing either the calcium binding protein parvalbumin (PV) or the neurotransmitter somatostatin (SST), are observed in the cortex and hippocampus of both patients with schizophrenia and rodent models used to study the disorder. Moreover, preclinical studies suggest that this loss of inhibitory function is a key pathological mechanism underlying the symptoms of schizophrenia. Interestingly, decreased expression of Lhx6, a key transcriptional regulator specific to the development and migration of PV and SST interneurons, is seen in human postmortem studies and following multiple developmental disruptions used to model schizophrenia preclinically. These results suggest that disruptions in interneuron development in utero may contribute to the pathology of the disorder. To recapitulate decreased Lhx6 expression during development, we used in utero electroporation to introduce an Lhx6 shRNA plasmid and knockdown Lhx6 expression in the brains of rats on gestational day 17. We then examined schizophrenia-like neurophysiological and behavioral alterations in the offspring once they reached adulthood. In utero Lhx6 knockdown resulted in increased ventral tegmental area (VTA) dopamine neuron population activity and a sex-specific increase in locomotor response to a psychotomimetic, consistent with positive symptomology of schizophrenia. However, Lhx6 knockdown had no effect on social interaction or spatial working memory, suggesting behaviors associated with negative and cognitive symptom domains were unaffected. These results suggest that knockdown of Lhx6 during development results in neurophysiological and behavioral alterations consistent with the positive symptom domain of schizophrenia in adult rats.

Region specific knockdown of Parvalbumin or Somatostatin produces neuronal and behavioral deficits consistent with those observed in schizophrenia

The anterior hippocampus and prefrontal cortex are regions linked to symptoms of schizophrenia. The anterior hippocampus is believed to be a key regulator of the mesolimbic dopamine system and is thought to be the driving force contributing to positive symptoms, while the prefrontal cortex is involved in cognitive flexibility and negative symptoms. Aberrant activity in these regions is associated with decreases in GABAergic markers, indicative of an interneuron dysfunction. Specifically, selective decreases are observed in interneurons that contain parvalbumin (PV) or somatostatin (SST). Here, we used viral knockdown in rodents to recapitulate this finding and examine the region-specific roles of PV and SST on neuronal activity and behaviors associated with positive, negative and cognitive symptoms. We found that PV and SST had differential effects on neuronal activity and behavior when knocked down in the ventral hippocampus (vHipp) or medial prefrontal cortex (mPFC). Specifically, SST or PV knockdown in the vHipp increased pyramidal cell activity of the region and produced downstream effects on dopamine neuron activity in the ventral tegmental area (VTA). In contrast, mPFC knockdown did not affect the activity of VTA dopamine neuron activity; however, it did produce deficits in negative (social interaction) and cognitive (reversal learning) domains. Taken together, decreases in PV and/or SST were sufficient to produce schizophrenia-like deficits that were dependent on the region targeted.

The profile of cognitive impairments in chronic ketamine users

The aim of this study was to examine the cognitive function in chronic ketamine users. Factors correlated to cognition impairments were analyzed. Sixty-three chronic ketamine users and 65 healthy subjects were recruited. Cognitive function was assessed by using immediate/delayed visual reproduction (IVR/DVR) tasks, immediate/delayed logical memory (ILM/DLM) tasks, Stroop test, Wisconsin card sorting test (WCST), and continuous performance test (CPT). Psychopathological symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS), Beck Depression Inventory (BDI) and Beck Anxiety Inventory (BAI). Ketamine users performed worse than controls on the IVR, ILM, DLM, Stroop and auditory CPT tests. IVR and DVR, color-naming and color-interference-reading scores were positively correlated with education level. In ketamine users ILM scores were negatively correlated with the negative subscale of PANSS. DLM score was positively correlated with average dose of ketamine use. Word-reading score was positively correlated with education level, and negatively correlated with duration of ketamine use. False hits in auditory CPT was positively correlated with duration of ketamine use. Number of trials to complete the first category and perseverative errors on WCST were positively correlated with the duration between the test and last ketamine use. Chronic ketamine users had cognitive impairments across multiple domains.

Influence of empathetic pain processing on cognition in schizophrenia

Deficits in both empathy and cognition have been reported widely in patients with schizophrenia. However, little is known about how these deficits interact among such patients. In the present study, we used pain portraying pictures preceding a color-word Stroop task to investigate the effect of empathetic pain observation on cognition among patients with schizophrenia. Twenty patients with schizophrenia and twenty healthy controls were included. The control group showed increased Stroop facilitation and decreased interference during the empathetic pain condition compared with the non-empathetic condition. Although patients with schizophrenia exhibited deficits in cognition, they demonstrated a similar empathy effect to controls on Stroop facilitation, but a somewhat larger empathy effect on Stroop interference (a more decreased effect). In particular, the groups did not differ in either automatic or controlled processing during the non-empathetic condition, suggesting general rather than specific cognitive deficits in schizophrenia. Together, we interpret our findings in terms of two opposing effects of empathy on cognition in schizophrenia, with possible neuromodulatory mechanism. Whereas prior studies showed empathy to be impaired, our outcomes indicate that at least some components of empathetic pain processing are preserved in such patients.

Dopamine in socioecological and evolutionary perspectives: implications for psychiatric disorders

Dopamine (DA) transmission in brain areas such as the prefrontal cortex (PFC) and nucleus accumbens (NAcc) plays important roles in cognitive and affective function. As such, DA deficits have been implicated in a number of psychiatric disorders such as schizophrenia and attention deficit/hyperactivity disorder (ADHD). Accumulating evidence suggests that DA is also involved in social behavior of animals and humans. Although most animals organize and live in social groups, how the DA system functions in such social groups of animals, and its dysfunction causes compromises in the groups has remained less understood. Here we propose that alterations of DA signaling and associated genetic variants and behavioral phenotypes, which have been normally considered as “deficits” in investigation at an individual level, may not necessarily yield disadvantages, but even work advantageously, depending on social contexts in groups. This hypothesis could provide a novel insight into our understanding of the biological mechanisms of psychiatric disorders, and a potential explanation that disadvantageous phenotypes associated with DA deficits in psychiatric disorders have remained in humans through evolution.

Spatial attentional control is not impaired in schizophrenia: Dissociating specific deficits from generalized impairments

A large literature has established that people with schizophrenia are impaired on tasks that require attentional control. However, evidence is mixed as to whether these impairments are specific deficits (Oltmanns & Neale, 1975) or merely reflect a generalized impairment (Dickinson & Harvey, 2009). Recent evidence also suggests visual attentional control for encoding into working memory may be selectively spared in people with schizophrenia (Gold et al., 2006). The current study used a cued backward masking task to investigate 23 people with schizophrenia and 27 healthy controls. People with schizophrenia were hypothesized to perform better on invalidly cued trials when making a simple identification or location judgment. However, we found schizophrenia impaired performance on both valid and invalid cues to the same degree whether the cue was a stored representation (top-down) or presented at the location of the stimulus (bottom-up). In contrast to a large neuropsychological literature, these findings suggest that people with schizophrenia show no specific spatial attentional control deficit. The errors that they make on such task may be consistent with a generalized impairment.

Persistence, diagnostic specificity and genetic liability for context-processing deficits in schizophrenia

Context-processing deficits have been shown in schizophrenia during first-episode, medication-naïve status, that persist after short-term antipsychotic treatment and also in first-degree relatives of individuals with schizophrenia. To confirm longer term persistence of deficits, we examined schizophrenia patients (n=63) during first-episode, medication-naïve status through to one-year follow-up, compared to healthy control (n=83) and non-schizophrenia psychosis comparison (n=47) groups, as well as unaffected first-degree relatives of individuals with schizophrenia (n=31). Context-processing ability was assessed by performance on the AX-CPT (Continuous Performance Test) at baseline, 8 weeks, 6 months, and 1 year (relatives only at baseline). Reaction time, error rates and signal detection indices (d'-context) of context processing were analyzed. Linear discriminant analyses (LDA) on early timepoints (baseline, 8 weeks) were conducted to predict confirmatory diagnosis (schizophrenia vs. psychosis control) at 6 months. Schizophrenia patients showed evidence of impaired context-processing relative to both the healthy and psychosis comparator groups at baseline and continued through to 1 year. While context-processing impairments persisted in schizophrenia patients through one year, the impairments in psychosis controls, which were more modest at baseline, remitted at follow-up. First-degree relatives showed deficits that were intermediate between the schizophrenia and healthy control groups. LDA showed 67% classification rates for distinguishing schizophrenia from non-schizophrenia psychosis. The persistence, diagnostic specificity and association with genetic liability give support for context processing impairments serving as a cognitive endophenotype for schizophrenia and evaluation of context processing could contribute to diagnostic assessments.

When top-down meets bottom-up: auditory training enhances verbal memory in schizophrenia

A critical research priority for our field is to develop treatments that enhance cognitive functioning in schizophrenia and thereby attenuate the functional losses associated with the illness. In this article, we describe such a treatment method that is grounded in emerging research on the widespread sensory processing impairments of schizophrenia, as described elsewhere in this special issue. We first present the rationale for this treatment approach, which consists of cognitive training exercises that make use of principles derived from the past 2 decades of basic science research in learning-induced neuroplasticity; these exercises explicitly target not only the higher order or "top-down" processes of cognition but also the content building blocks of accurate and efficient sensory representations to simultaneously achieve "bottom-up" remediation. We then summarize our experience to date and briefly review our behavioral and serum biomarker findings from a randomized controlled trial of this method in outpatients with long-term symptoms of schizophrenia. Finally, we present promising early psychophysiological evidence that supports the hypothesis that this cognitive training method induces changes in aspects of impaired bottom-up sensory processing in schizophrenia. We conclude with the observation that neuroplasticity-based cognitive training brings patients closer to physiological patterns seen in healthy participants, suggesting that it changes the brain in an adaptive manner in schizophrenia.

Individual differences in psychotic effects of ketamine are predicted by brain function measured under placebo

The symptoms of major psychotic illness are diverse and vary widely across individuals. Furthermore, the prepsychotic phase is indistinct, providing little indication of the precise pattern of symptoms that may subsequently emerge. Likewise, although in some individuals who have affected family members the occurrence of disease may be predicted, the specific symptom profile may not. An important question, therefore, is whether predictive physiological markers of symptom expression can be identified. We conducted a placebo-controlled, within-subjects study in healthy individuals to investigate whether individual variability in baseline physiology, as assessed using functional magnetic resonance imaging, predicted psychosis elicited by the psychotomimetic drug ketamine and whether physiological change under drug reproduced those reported in patients. Here we show that brain responses to cognitive task demands under placebo predict the expression of psychotic phenomena after drug administration. Frontothalamic responses to a working memory task were associated with the tendency of subjects to experience negative symptoms under ketamine. Bilateral frontal responses to an attention task were also predictive of negative symptoms. Frontotemporal activations during language processing tasks were predictive of thought disorder and auditory illusory experiences. A subpsychotic dose of ketamine administered during a second scanning session resulted in increased basal ganglia and thalamic activation during the working memory task, paralleling previous reports in patients with schizophrenia. These results demonstrate precise and predictive brain markers for individual profiles of vulnerability to drug-induced psychosis.

Functional brain abnormalities in psychiatric disorders: neural mechanisms to detect and resolve cognitive conflict and interference

In the present article, we review functional neuroimaging studies on interference processing and performance monitoring in three groups of psychiatric disorders, (1) mood disorders, (2) schizophrenia, and (3) obsessive-compulsive disorder (OCD). Ad (1) Behavioral performance measures suggest an impaired interference resolution capability in symptomatic bipolar disorder patients. A series of neuroimaging analyses found alterations in the ACC-DLPFC system in mood disorder (unipolar depressed and bipolar) patients, putatively reflective of an abnormal interplay of monitoring and executive neurocognitive functions. Other studies of euthymic bipolar patients showed relatively decreased interference-related activation in rostroventral PFC which conceivably underlies defective inhibitory control. Ad (2) Behavioral Stroop studies revealed a specific performance pattern of schizophrenia patients (normal RT interference but increased error interference and RT facilitation) suggestive of a deficit in ignoring irrelevant (word) information. Moreover, reduced/absent behavioral post-error and post-conflict adaptation effects suggest alterations in performance monitoring and/or adjustment capability in these patients. Neuroimaging findings converge to suggest a disorder-related abnormal neurophysiology in ACC which consistently showed conflict- and error-related hypoactivation that, however, appeared to be modulated by different factors. Moreover, studies suggest a specific deficit in context processing in schizophrenia, evidently related to activation reduction in DLPFC. Ad (3) Behavioral findings provide evidence for impaired interference resolution in OCD. Neuroimaging results consistently showed conflict- and error-related ACC hyperactivation which--conforming OCD pathogenesis models--can be conclusively interpreted as reflecting overactive performance monitoring. Taken together, interference resolution and performance monitoring appeared to be fruitful concepts in the investigation of neurocognitive deficits in psychiatric disorders.

Accounting for cognitive aging: context processing, inhibition or processing speed?

Age-related deficits in context processing were examined in relationship to two predominant theories of cognitive aging (the Inhibitory Deficit and Processing Speed Models). Older and younger adults completed a measure of context processing (AX Continuous Performance Test (CPT) task) as well as a computerized battery of inhibitory tasks: Stroop, garden path sentences, go no-go, and the stop-signal paradigm. Participants also completed a simple processing speed task. After controlling for baseline differences in processing speed, age effects were detected on the AX-CPT. Smaller, but significant age effects were noted on the Stroop and stop-signal tasks, but no significant age effects were found on the garden path sentence and go no-go tasks. Intertask correlations were weak, providing little evidence for a homogenous or uniform construct of inhibition. The sensitivity of the AX-CPT to cognitive aging is discussed in the context of existing theories of cognitive aging. The authors suggest that deficits in context processing and utilization may underlie cognitive aging phenomena.

Pharmacogenetic tools for the development of target-oriented cognitive-enhancing drugs

The identification of the anatomical and physiological substrates involved in the regulation of the dorsolateral prefrontal cortex function in humans provided the basis for the understanding of mechanisms involved in cognitive and executive function under normal as well as pathological conditions. In this context, substantial evidence indicates that alterations in monaminergic function in the dorsolateral prefrontal cortex significantly contributes to the cognitive impairments present in schizophrenia, attention deficit disorders, and other neuropsychiatric conditions. The development of a number of compounds that selectively increase extracellular dopamine (DA) concentrations in the dorsolateral prefrontal cortex but not in subcortical areas by either blocking its metabolism or reuptake, or increasing its release, or that directly activate postsynaptic DA-1 receptor mechanisms provided powerful pharmacotherapeutic tools to mitigate the cognitive deficits brought about by the dopaminergic alterations of the prefrontal cortex. More recently, the findings that polymorphisms of the catecholamine-O-methyl-transferase gene may also modify the effect of these drugs on the prefrontal cortex points toward a more specific genotype-based neuropsychopharmacology for the treatment of cognitive deficits in schizophrenia as well as in a number of other neuropsychiatric conditions. The ability of these compounds to increase DA load selectively in the frontal cortex and not on subcortical systems allows a targeted intervention without the stimulant-like effects observed with older drugs used to treat those conditions.

Evidence that specific executive functions predict symptom variance among schizophrenia patients with a predominantly negative symptom profile

INTRODUCTION

Although deficits in executive functioning in schizophrenia have been consistently reported, their precise relationship to symptomatology remains unclear. Recent approaches to executive functioning in nonschizophrenia studies have aimed to "fractionate" the individual cognitive processes involved. In this study, we hypothesised that if these processes are fractionable, then particular symptom syndromes may be selectively related to executive deficits. In particular, it was hoped that this approach could clarify whether negative and positive symptoms of schizophrenia are differentially related to particular aspects of executive/attentional functions.

METHODS

A total of 32 patients with schizophrenia and 16 matched controls were assessed on a series of tasks designed to tap the theoretically derived executive functions of Inhibition, Shifting set, Working memory, and Sustained attention.

RESULTS

Negative symptoms were significantly predicted by performance on an "Inhibition" task (Stroop), and not by performance on any other task. Furthermore, for a subgroup of patients with predominantly negative symptoms variance in positive symptoms was only significantly predicted by performance on a set-shifting task (Visual Elevator), and not by performance on other tasks, including inhibition.

CONCLUSIONS

Our results support the contention that negative symptoms can, at least partly, be conceived of as cognitive behaviours expressing specific executive deficits. Specifically, we discuss the possibility that negative symptoms may, in part, express a failure in response monitoring. We further suggest that the disordered metacognition resulting in positive symptoms may be mediated by cognitive flexibility in patients with a predominantly negative symptom profile.

Movement planning deficits in schizophrenia: failure to inhibit automatic response tendencies

INTRODUCTION

Explicit planning deficits have been reported frequently in patients with schizophrenia. This study addressed the question whether these patients would already encounter difficulties in a more "implicit" process of planning an optimal sequence of movements in simple actions.

METHODS

Twenty patients with schizophrenia and 20 controls participated in the study. The motor tasks consisted of copying simple line drawings in which the planning of a movement sequence was taxed along various dimensions. In the first task the number of line elements varied between one and two, and the two-line figures differed with respect to the ease with which the so-called graphic production rules could be applied. In the second task the spatial position of the drawing varied between an easy centre position and a somewhat more difficult corner location. In the third task, subjects were asked to start copying either at a preferred or at a less preferred starting point.

RESULTS

The results showed that the patients did not encounter planning difficulties while copying the one- or two-segment patterns. However, the variations in the spatial conditions and starting point did affect the patients' performance more than that of the controls. Whereas the patients with higher negative symptom scores tended to be slower when they were forced to start drawing at a particular point, the patients predominantly exhibiting features of disorganisation proved to be faster in this condition.

CONCLUSIONS

The findings suggest a fairly intact initiation of simple movement sequences in patients with schizophrenia, but difficulties in inhibiting automatic response tendencies. It is concluded that this inhibition failure may play an important role in the planning difficulties these patients experience.

Amphetamine improves cognitive function in medicated individuals with schizophrenia and in healthy volunteers

BACKGROUND

Recent research on schizophrenia indicates that cognitive deficits in this illness are important predictors of functional outcome, highlighting the need for treatments that have a positive impact on cognitive function. Here we explore the hypothesis that acute administration of d-amphetamine can improve cognitive function in individuals with schizophrenia who are well-treated with typical antipsychotics, as well as in healthy controls performing under dual task conditions designed to elicit performance deficits analogous to those found in schizophrenia.

METHODS

Ten individuals with schizophrenia taking haldol or prolixin and 22 healthy controls performed spatial working memory, language production, and Stroop tasks under both placebo and 0.25 mg/kg of D-amphetamine.

RESULTS

D-Amphetamine improved reactions times on the spatial working memory and Stroop tasks for both individuals with schizophrenia and controls, and improved working memory accuracy in schizophrenia. In addition, D-amphetamine improved language production for both individuals with schizophrenia and controls.

CONCLUSIONS

These results provide support for the hypothesis that the adjunctive administration of dopamine agonist can improve cognitive in individuals with schizophrenia taking typical antipsychotics. The results are discussed in terms of their implications for understanding the nature of working memory deficits in schizophrenia, and potential future avenues for cognitive enhancement in this illness.

Targeting synapses and myelin in the prevention of schizophrenia

Many of the functions that are mediated by the prefrontal cortex (PFC) are severely impaired in schizophrenia. The maturation of these functions takes place during late adolescence and early adulthood, which coincides with the period of time when overt symptomatology of schizophrenia most commonly emerges. Two developmental processes occurring during the periadolescence period appear to mediate the functional maturation of the PFC: pruning of exuberant synapses and myelination of axons. It has long been speculated in the literature that disturbances of these processes may result in dysfunction of the PFC and thereby trigger the emergence of symptoms and deficits of schizophrenia. Alternatively, but not mutually exclusively, it has also been suggested that these late developmental processes may not be aberrant but they "unmask" preexisting deficits in the PFC, resulting in the onset of symptoms. The important implication of both of these scenarios is that in either case the emergence of PFC functional disturbances and the onset of symptoms and deficits of schizophrenia would in theory be preventable by pharmacologic manipulation of the synaptic pruning and/or axonal myelination processes. Thus, better understanding of the cellular and molecular mechanisms that mediate these processes will provide truly novel insight into the therapeutics and prevention of schizophrenia.

Differential impairment of working memory performance in first-degree relatives of individuals with schizophrenia

BACKGROUND

Numerous studies have reported neuropsychological impairment in schizophrenia and increasing evidence suggests that individuals with schizophrenia or schizophrenia spectrum disorders and their unaffected first-degree family members exhibit similar deficits in some neuropsychological domains. Substantial modifications to the Wechsler Memory Scale (WMS) have resulted in more sensitive and reliable indicators of various aspects of memory functioning in the WMS-III, which enables generation of auditory, visual and working memory indices.

OBJECTIVE

The aim of the present study was to examine the memory profile of individuals with schizophrenia or schizophrenia spectrum disorder (n = 19), their unaffected first-degree family members (n = 11), and healthy controls (n = 9).

METHODS

The study involved neuropsychological testing, including the immediate and working memory subtests of the WMS-III, utilizing both auditory and visual domains. Symptom assessment was performed using the Schedules for Clinical Assessment in Neuropsychiatry (SCAN), version 2.0. Two multivariate analyses of covariance (mancova) were conducted: (i) comparing patients, relatives and controls; and (ii) comparing relatives and controls only.

RESULTS

The first analysis indicated that the patient group obtained significantly lower index scores than both relatives and controls on all three indices. The second analysis indicated that the performance of relatives was significantly lower than controls on the working memory index, although there were no significant differences on the auditory and visual immediate index scores.

CONCLUSIONS

The differential impairment in working memory performance in clinically asymptomatic family members suggests that the WMS-III working memory index score may be a potential phenotypic marker of schizophrenia.

Context-Processing Deficits in Schizotypal Personality Disorder

Research suggests that schizotypal personality disorder (SPD) is a part of the spectrum of schizophrenia-related illnesses. This article hypothesizes that a deficit in the representation and maintenance of context is a core cognitive disturbance in schizophrenia and that SPD individuals should demonstrate context-processing deficits. To test this hypothesis, the authors administered 3 versions of their AX-CPT task, designed to assess context processing, to 35 healthy controls and 26 individuals with DSM-IV SPD. They also administered working memory and selective attention tasks. SPD individuals displayed context representation deficits similar to those found in schizophrenia but did not show the same additional deficits in context maintenance. Context processing was strongly associated with working memory and selective attention performance in the SPD individuals.

Thought disorder in schizophrenia: working memory and impaired context

This research was designed to provide data on whether thought disorder in schizophrenia patients is due to difficulty in holding external stimuli or the external context online in working memory. We assessed 231 early phase acute inpatients, including 68 schizophrenic patients and 38 bipolar manic patients. Patients were administered a thought disorder test that requires holding stimuli online in working memory as they respond and another in which the stimuli is in direct view of the patients throughout the test procedure. The results indicated that patients who were thought disordered on the test requiring holding the external stimuli online in memory also were more thought disordered on the test that provides full vision of the stimuli throughout the testing (p < 0.001). Thus, schizophrenia patients vulnerable to thought disorder show thought disorder regardless of whether or not they are required to hold the stimuli online in memory. Overall, the data did not support the formulation that thought disorder is primarily a consequence of failure to hold external stimuli or contextual material online in working memory. An alternate view of thought disorder is presented.

Neurophysiological Evidence for Disturbances of Conflict Processing in Patients With Schizophrenia

Deficits in cognition are a hallmark of schizophrenia. In the present study, the authors investigated the effects of schizophrenia on the neural correlates of conflict processing in a single-trial version of the Stroop task by using event-related brain potentials. Relative to matched controls, patients with schizophrenia showed increased Stroop interference in response time, but this effect was eliminated when the effect of response slowing was controlled. In controls, conflict processing was associated with a negative wave peaking between 400 and 500 ms (N450) and conflict sustained potential (SP) peaking between 600 and 800 ms after stimulus onset. In patients with schizophrenia, the amplitude of the N450 was significantly attenuated and the conflict SP was absent. These results provide evidence for the existence of altered neural processes associated with conflict processing that may be associated with dysfunction of the anterior cingulate and prefrontal cortex in patients with schizophrenia.

Working and long-term memory deficits in schizophrenia: is there a common prefrontal mechanism?

This study tested the hypothesis that dorsolateral prefrontal cortex deficits contribute to both working memory and long-term memory disturbances in schizophrenia. It also examined whether such deficits were more severe for verbal than nonverbal stimuli. Functional magnetic resonance imaging was used to assess cortical activation during performance of verbal and nonverbal versions of a working memory task and both encoding and recognition tasks in 38 individuals with schizophrenia and 48 healthy controls. Performance of both working memory and long-term memory tasks revealed disturbed dorsolateral prefrontal cortex activation in schizophrenia, although medial temporal deficits were also present. Some evidence was found for more severe cognitive and functional deficits with verbal than nonverbal stimuli, although these results were mixed.

Prefrontal neurons and the genetics of schizophrenia

This article reviews prefrontal cortical biology as it relates to pathophysiology and genetic risk for schizophrenia. Studies of prefrontal neurocognition and functional neuroimaging of prefrontal information processing consistently reveal abnormalities in patients with schizophrenia. Abnormalities of prefrontal information processing also are found in unaffected individuals who are genetically at risk for schizophrenia, suggesting that genetic polymorphisms affecting prefrontal function may be susceptibility alleles for schizophrenia. One such candidate is a functional polymorphism in the catechol-o-methyl transferase (COMT) gene that markedly affects enzyme activity and that appears to uniquely impact prefrontal dopamine. The COMT genotype predicts performance on prefrontal executive cognition and working memory tasks. Functional magnetic resonance imaging confirms that COMT genotype affects prefrontal physiology during working memory. Family-based association studies have revealed excessive transmission to schizophrenic offspring of the allele (val) related to poorer prefrontal function. These various data provide convergent evidence that the COMT val allele increases risk for schizophrenia by virtue of its effect on dopamine-mediated prefrontal information processing-the first plausible mechanism for a genetic effect on normal human cognition and risk for mental illness.