Functional hypofrontality and working memory dysfunction in schizophrenia

Mitochondrial complex I subunits expression is altered in schizophrenia: a postmortem study

BACKGROUND

Several independent lines of evidence indicate mitochondrial dysfunction in schizophrenia in the brain and periphery, including mitochondrial hypoplasia, dysfunction of the oxidative phosphorylation system, and altered mitochondrial-related gene expression.

METHODS

In this study, three subunits of mitochondrial complex I were analyzed at the level of mRNA and protein in postmortem brain specimens from the prefrontal and the ventral parietooccipital cortex of patients with schizophrenia, major depression, bipolar disorder, and normal control subjects.

RESULTS

Both mRNA and protein levels of the 24-kDa and 51-kDa subunits of complex I were significantly decreased in the prefrontal cortex, but increased in the ventral parietooccipital cortices of schizophrenia patients compared with normal control subjects. In the latter region, protein levels of both subunits were increased in bipolar patients as well, being in line with the significant overlap in clinical symptoms between schizophrenia and bipolar patients. No change was observed in the 75-kDa subunit expression in the prefrontal cortex.

CONCLUSIONS

The schizophrenia-specific reduction in complex I subunits in the prefrontal cortex is consistent with one of schizophrenia's most prominent deficits, namely, hypofrontality, thus further supporting the hypothesis of mitochondrial dysfunction in this disorder. The abnormal, bidirectional expression of complex I in various brain regions, rather than in a circumscribed area, supports the idea of impaired cerebral circuitry in schizophrenia.

Functional magnetic resonance imaging during auditory verbal working memory in nonpsychotic relatives of persons with schizophrenia: a pilot study

BACKGROUND

First-degree relatives of persons with schizophrenia carry elevated genetic risk for the illness and show deficits on high-load information processing tasks. We used functional magnetic resonance imaging (fMRI) to test whether nonpsychotic relatives show altered functional activation in the prefrontal cortex (PFC), thalamus, hippocampus, and anterior cingulate during a working memory task requiring interference resolution.

METHODS

Twelve nonpsychotic relatives of persons with schizophrenia and 12 healthy control subjects were administered an auditory, verbal working memory version of the Continuous Performance Test during fMRI. An asymmetric, spin-echo, T2*-weighted sequence (15 contiguous, 7-mm axial slices) was acquired on a full-body MR scanner. Data were analyzed by Statistical Parametric Mapping (SPM).

RESULTS

Compared with control subjects, relatives showed greater task-elicited activation in the PFC and the anterior and dorsomedial thalamus. When task performance was controlled, relatives showed significantly greater activation in the anterior cingulate. When effects of other potentially confounding variables were controlled, relatives generally showed significantly greater activation in the dorsomedial thalamus and anterior cingulate.

CONCLUSIONS

This pilot study suggests that relatives of persons with schizophrenia have subtle differences in brain function in the absence of psychosis. These differences add to the growing literature identifying neurobiological vulnerabilities to schizophrenia.

Synaptogenesis and heritable aspects of executive attention

In humans, changes in brain structure and function can be measured non-invasively during postnatal development. In animals, advanced optical imaging measures can track the formation of synapses during learning and behavior. With the recent progress in these technologies, it is appropriate to begin to assess how the physiological processes of synapse, circuit, and neural network formation relate to the process of cognitive development. Of particular interest is the development of executive function, which develops more gradually in humans. One approach that has shown promise is molecular genetics. The completion of the human genome project and the human genome diversity project make it straightforward to ask whether variation in a particular gene correlates with variation in behavior, brain structure, brain activity, or all of the above. Strategies that unify the wealth of biochemical knowledge pertaining to synapse formation with the functional measures of brain structure and activity may lead to new insights in developmental cognitive psychology.

Executive dysfunctions as potential markers of familial vulnerability to bipolar disorder and schizophrenia

Attentional and executive impairments have been found both in patients with schizophrenia and in their unaffected first-degree relatives, suggesting that they might be considered as familial vulnerability markers. Several studies have shown that the performance of bipolar patients does not significantly differ from that of schizophrenic patients, so that executive and attentional deficits might not be specific to schizophrenia. In the present study, we aimed to identify executive dysfunctions in schizophrenia and bipolar disorder that might be vulnerability trait markers specific to one or common to both of these diseases. We assessed cognitive performance of euthymic bipolar and schizophrenic patients, their unaffected first-degree relatives and a healthy control group, using neuropsychological tasks to test different components of executive function: the Verbal Fluency Test, the Stroop Word Colour Test, the Wisconsin Card Sorting Test and the Trail Making Test. The two groups of patients and their unaffected relatives demonstrated disproportionately increased slowness on the Stroop test in comparison to the normal healthy group. Patients with schizophrenia performed poorly on all the tests in comparison to the normal healthy subjects, while no other impairment was observed in the bipolar patients and in the relatives of schizophrenic and bipolar patients. Enhanced susceptibility to interference and reduced inhibition could be transnosographical markers for a shared familial vulnerability common to schizophrenia and bipolar disorders.

GABA and schizophrenia: a review of basic science and clinical studies

BACKGROUND

A converging body of evidence implicates the gamma-aminobutyric acid (GABA) neurotransmitter system in the pathogenesis of schizophrenia.

METHODS

The authors review neuroscience literature and clinical studies investigating the role of the GABA system in the pathophysiology of schizophrenia. First, a background on the GABA system is provided, including GABA pharmacology and neuroanatomy of GABAergic neurons. Results from basic science schizophrenia animal models and human studies are reviewed. The role of GABA in cognitive dysfunction in schizophrenia is then presented, followed by a discussion of GABAergic compounds used in monotherapy or adjunctively in clinical schizophrenia studies.

RESULTS

In basic studies, reductions in GABAergic neuronal density and abnormalities in receptors and reuptake sites have been identified in several cortical and subcortical GABA systems. A model has been developed suggesting GABA's role (including GABA-dopamine interactions) in schizophrenia. In several clinical studies, the use of adjunctive GABA agonists was associated with greater improvement in core schizophrenia symptoms.

CONCLUSIONS

Alterations in the GABA neurotransmitter system are found in clinical and basic neuroscience schizophrenia studies as well as animal models and may be involved in the pathophysiology of schizophrenia. The interaction of GABA with other well-characterized neurotransmitter abnormalities remains to be understood. Future studies should elucidate the potential therapeutic role for GABA ligands in schizophrenia treatment.

Hippocampal deformities in the unaffected siblings of schizophrenia subjects

BACKGROUND

Neuroanatomical abnormalities have been reported in schizophrenia subjects and their relatives and may be related to genetic vulnerability. The objective of this study was to further elucidate hippocampal deformities as a marker of genetic vulnerability for schizophrenia.

METHODS

Magnetic resonance scans were collected in 13 pairs of schizophrenics and their unaffected siblings from families with multiple affected members, in 12 schizophrenics from families without another affected member, and in 10 healthy controls. Hippocampal volume and shape were compared using large-deformation high-dimensional brain mapping.

RESULTS

Decreases in hippocampal volume, covaried for total cerebral volume, were observed in the schizophrenia subjects from families with multiple affected members, as well as in their unaffected siblings. Shape analysis demonstrated that both groups of schizophrenia subjects, as well as the unaffected siblings, could be distinguished from the controls; however, no significant difference in hippocampal shape was found between the schizophrenia subjects and their unaffected siblings. Visualization of the pattern of hippocampal shape deformity in both groups of schizophrenia subjects and in the unaffected siblings showed inward deformities of the head of the hippocampus.

CONCLUSIONS

Deformations of hippocampal anatomy may be related to the genetic vulnerability of acquiring schizophrenia.

Wisconsin Card Sorting Test performance in schizophrenia: the role of working memory

Schizophrenia typically results in reduced performance on the Wisconsin Card Sorting Test (WCST). In the current study, we used a variety of approaches to examine the role of working memory (WM) in this deficit. One approach was to examine patterns of perseverative and non-perseverative errors. A second approach involved the comparison of the standard WCST to a modified version that used visual cues to reduce demands on WM. A third approach was to quantify the impact of WM demands on performance on a trial by trial basis. Consistent with theories of WM, the schizophrenia group showed increases in both perseverative and non-perseverative errors and differences between individuals with schizophrenia and controls were largest when WM demands were high. The visual cues helped the schizophrenia group overcome the high WM demands of the test, although they did not reduce the impairment in terms of standard scoring procedures. All impairments disappeared, however, after controlling for group differences on a measure of the speed of encoding information in WM. The pattern of results supports the conclusion that WM impairment contributes to poor performance on the WCST in individuals with schizophrenia, with additional evidence that this impairment results from generalized slowing of information processing.

Altered auditory processing in acutely psychotic never-medicated first-episode patients

Individuals with psychosis fail to differentiate external impulses and suffer from distortions of reality testing. Schizophrenia group illnesses are also associated with deficits in working memory and perception. We examined the manifestations of a very early phase of psychotic illness to automatic auditory deviance detection to clarify the basic mechanisms underlying misinterpretations of perception.

METHODS

Twenty-five never-medicated patients admitted for hospital evaluation of acute psychosis were studied. Fifty-eight EEG channels were recorded during an auditory oddball paradigm. Event-related potentials (ERPs) time-locked to non-attended deviant auditory stimuli were studied in patients and compared with healthy controls. Auditory processing was examined both at the level of the measured biosignals (standard and deviant responses) and with subtraction waveforms. Topographical differences were characterized using global field power (GFP) and minimum norm estimates.

RESULTS

The maximum GFP amplitudes and mean amplitudes of the 58 channels within the time windows corresponding to the previously known 'N2b', 'P3a' and 'P3b' components were clearly reduced in patients when compared to healthy controls. However, the groups did not differ during attention-independent automatic processing corresponding to the 'N1' and 'MMN' components, or with respect to the peak latencies of the GFP maxima.

CONCLUSIONS

Impairment of the processing of a deviance in simple auditory input in acutely ill drug-naive first-episode psychotic patients only appears in attention-dependent processing after about 250 ms. The alterations in auditory processing differed between stimulus types, suggesting at least two mechanisms underlying the auditory discrimination impairments in acute psychosis. After 250 ms there was a linear and gradually increasing difference in magnitude between the groups in their responses to deviant stimuli, probably related to arousal. In addition, however, there was a striking difference between the groups in the processing of standard stimuli. The early processing was similar in patients and controls, but the striking difference appeared in later processing. The sensory memory deficits associated with psychosis may be explained by an abnormality in sensory model formation rather than by impaired deviant detection.

Neurobiology of emotion perception II: Implications for major psychiatric disorders

To date, there has been little investigation of the neurobiological basis of emotion processing abnormalities in psychiatric populations. We have previously discussed two neural systems: 1) a ventral system, including the amygdala, insula, ventral striatum, ventral anterior cingulate gyrus, and prefrontal cortex, for identification of the emotional significance of a stimulus, production of affective states, and automatic regulation of emotional responses; and 2) a dorsal system, including the hippocampus, dorsal anterior cingulate gyrus, and prefrontal cortex, for the effortful regulation of affective states and subsequent behavior. In this critical review, we have examined evidence from studies employing a variety of techniques for distinct patterns of structural and functional abnormalities in these neural systems in schizophrenia, bipolar disorder, and major depressive disorder. In each psychiatric disorder, the pattern of abnormalities may be associated with specific symptoms, including emotional flattening, anhedonia, and persecutory delusions in schizophrenia, prominent mood swings, emotional lability, and distractibility in bipolar disorder during depression and mania, and with depressed mood and anhedonia in major depressive disorder. We suggest that distinct patterns of structural and functional abnormalities in neural systems important for emotion processing are associated with specific symptoms of schizophrenia and bipolar and major depressive disorder.

Right lateral fusiform gyrus dysfunction during facial information processing in schizophrenia

BACKGROUND

Patients with schizophrenia exhibit facial information processing deficits that likely contribute to their social dysfunction. Whether the deficits involve facial affect and/or identity processing or result from other cognitive abnormalities in schizophrenia remains controversial, and a brain dysfunction specifically related to them has never been reported. If such dysfunction existed, it should be consistently observed across groups of patients and during performance of different facial information processing tasks, independently of whether such tasks demand working memory (WM), semantic, or other cognitive processes. We hypothesized that the right lateral fusiform gyrus (rLFG), one of several human brain areas involved in facial information processing, would consistently show activation abnormalities during both facial affect and identity discrimination in schizophrenia.

METHODS

We used functional magnetic resonance imaging to measure brain activation in two groups of six chronic, stable schizophrenic outpatients and two of six age- and gender-matched healthy controls. One group of patients and one of controls performed facial affect-with or without semantic processing-and identity discrimination tasks, and the other two groups WM tasks with facial expression cues and varying attentional demands.

RESULTS

Patients from either group failed to activate the rLFG when compared to controls in any task. Other activation abnormalities were task-specific (i.e., seen only during performance of one set of tasks) and not consistently observed in both groups of patients, and thus could not be directly and solely linked to facial information discrimination.

CONCLUSIONS

These results indicate a specific rLFG dysfunction during early facial information--identity or affect--processing, independent from other cognitive deficits, in schizophrenia.

No hypofrontality, but absence of prefrontal lateralization comparing verbal and spatial working memory in schizophrenia

Hypofrontality and decreased lateralization have been two major, albeit controversial, results from functional neuroimaging studies of schizophrenia. We used fMRI to study cortical activation during a verbal and spatial working memory (WM) task (2-back) in 15 inpatients acutely ill with schizophrenia and 15 matched control subjects. We hypothesized (i) hypofrontality in patients in both tasks and (ii) decreased lateralization of prefrontal activation in patients under the assumption that, in controls, left prefrontal cortex (PFC) is engaged preferentially in the verbal task (verbal domain dominance) and the right prefrontal cortex is engaged preferentially in the spatial task (spatial domain dominance). Our results showed no significant differences in frontal activation between controls and patients, i.e. no hypofrontality in patients, even at a very liberal threshold (p<0.01). This may be explained by the fact that nearly all patients studied received atypical neuroleptics. Nonetheless, we found evidence for more subtle, domain-related prefrontal dysfunction. Whereas controls showed verbal WM domain dominance in left inferior frontal cortex and spatial WM domain dominance in right prefrontal cortex, these domain dominance effects were absent in the patient group, i.e. there were no lateralization effects. Finally, only patients showed an inverse correlation between performance and right prefrontal activation in verbal WM. We conclude that the finding of hypofrontality may depend on the medication of the patients and that there is prefrontal dysfunction even in the absence of hypofrontality.

Genetically mediated brain abnormalities in schizophrenia

Schizophrenia is a highly heritable, neurobehavioral disorder; however, the mode of inheritance is complex, and linkage findings have been difficult to replicate. Some consistent linkage findings have emerged on chromosomes 1, 6, 8, 11, 13, 15, and 22. New methods are being developed for candidate gene identification, including the use of neurobiologic phenotypes observed in relatives of persons with schizophrenia. Neuroimaging studies of relatives implicate abnormal hippocampal structure and inefficient prefrontal network functioning, probably representing mild variants of the abnormalities observed in schizophrenia. These characteristics may represent stable markers of vulnerability to schizophrenia, because they are not confounded by effects of antipsychotic drugs or psychosis. Recent studies provide evidence for a small role of the catechol-O-methyltransferase gene on 22q, and the serotonin receptor transporter gene on 17q11-q12 in the development of schizophrenia. Linking genes and brain regions or networks is an important step in identification of the pathophysiology of schizophrenia.

Brain activation patterns during a selective attention test-a functional MRI study in healthy volunteers and patients with schizophrenia

Functional magnetic resonance imaging was used to compare cortical activation patterns in healthy volunteers with those in patients with schizophrenia during a modified verbal Stroop task. Healthy subjects (n=13) and patients with schizophrenia (n=13) on stable antipsychotic treatment, matched on demographic variables, were included. Patients were preselected on the basis of good performance on a selective attention test. Patients with schizophrenia showed a significantly increased pattern of activation in the left and right inferior frontal cortex and the anterior cingulate cortex. A significant negative correlation between activation of the left prefrontal cortex and accuracy in the modified Stroop test was observed for healthy controls but not schizophrenia patients. Although both groups recruited the prefrontal cortex during the modified Stroop task, for the schizophrenia patients this activation was bilateral, whereas for the controls this activation was primarily in the left hemisphere, suggesting that patients with schizophrenia recruited more prefrontal regions to perform the task with the same accuracy as healthy controls. Our findings of increased activity across multiple areas of the brain, including dorsolateral frontal cortex and anterior cingulate, in patients with schizophrenia who perform relatively well on a task of selective attention give further evidence that task performance may be a confounding factor in the interpretation of neuroimaging results.

Catechol-O-methyltransferase genotype and dopamine regulation in the human brain

A functional polymorphism in the gene for catechol-O-methyltransferase (COMT) has been shown to affect executive cognition and the physiology of the prefrontal cortex in humans, probably by affecting prefrontal dopamine signaling. The COMT valine allele, associated with relatively poor prefrontal function, is also a gene that may increase risk for schizophrenia. Although poor performance on executive cognitive tasks and abnormal prefrontal function are characteristics of schizophrenia, so is psychosis, which has been related to excessive presynaptic dopamine activity in the striatum. Studies in animals have shown that diminished prefrontal dopamine neurotransmission leads to upregulation of striatal dopamine activity. We measured tyrosine hydroxylase (TH) mRNA in mesencephalic dopamine neurons in human brain and found that the COMT valine allele is also associated with increased TH gene expression, especially in neuronal populations that project to the striatum. This indicates that COMT genotype is a heritable aspect of dopamine regulation and it further explicates the mechanism by which the COMT valine allele increases susceptibility for psychosis.

Prefrontal cortex dysfunction during working memory performance in schizophrenia: reconciling discrepant findings

Working memory (WM) deficits are a persistent, disabling and relatively treatment-resistant feature of schizophrenia that may underlie many cognitive deficits and symptoms. They are associated with prefrontal cortex dysfunction. While most neuroimaging studies of WM demonstrate "task-related hypofrontality" in schizophrenic relative to healthy subjects, several recent studies have reported equal or increased prefrontal activity. These findings challenge central assumptions regarding cognitive deficits and prefrontal cortex dysfunction in schizophrenia. The goal of this review is to reconcile these seemingly discrepant findings. Methodological factors addressed include the use of intersubject averaging, WM task parameters and the reliability of the measures. Factors intrinsic to schizophrenia and their relevance to the selection of experimental methods and the interpretation of group data are also discussed. Both hypo- and hyperfrontality are hypothesized to be valid and informative reflections of prefrontal cortex dysfunction in schizophrenia. Due to the heterogeneity and variability of both performance and regional recruitment in schizophrenia, whether individual data is considered, the level and type of WM demands and the composition of the sample with regard to performance deficits all influence study outcome and contribute to discrepancies. Although the prefrontal cortex is consistently implicated in WM deficits, the basis of its dysfunction and its exact contribution remain unclear. Future work might focus on delineating the exact WM processes, domains and components that are deficient. In addition, variability in behavior and activation might best be regarded as intrinsic to schizophrenia and having a neural basis that requires explanation. In combination with other techniques, neuroimaging can identify the neural circuitry responsible for WM deficits and elucidate the contribution of each anatomical component.

Working memory and prefrontal cortex dysfunction: specificity to schizophrenia compared with major depression

BACKGROUND

A large number of studies suggest the presence of deficits in dorsolateral prefrontal cortex function during performance of working memory tasks in individuals with schizophrenia. However, working memory deficits may also present in other psychiatric disorders, such as major depression. It is not clear whether people with major depression also demonstrate impaired prefrontal activation during performance of working memory tasks.

METHODS

We used functional magnetic resonance imaging to assess the patterns of cortical activation associated with the performance of a 2-back version of the N-Back task (working memory) in 38 individuals with schizophrenia and 14 with major depression.

RESULTS

We found significant group differences in the activation of dorsolateral prefrontal cortex associated with working memory performance. Consistent with prior research, participants with schizophrenia failed to show activation of right dorsolateral prefrontal cortex in response to working memory tasks demands, whereas those with major depression showed clear activation of right and left dorsolateral prefrontal cortex as well as bilateral activation of inferior and superior frontal cortex.

CONCLUSIONS

During performance of working memory tasks, deficits in prefrontal activation, including dorsolateral regions, are more severe in participants with schizophrenia (most of whom were recently released outpatients) than in unmedicated outpatients with acute nonpsychotic major depression.

Higher scores of self reported schizotypy in healthy young males carrying the COMT high activity allele

The gene for COMT is located on chromosome 22q11, an area that has been implicated in the pathogenesis of schizophrenia through linkage studies and through the detection of deletions in schizophrenics and velocardiofacial syndrome patients that often present psychotic symptomatology. Additionally catechol-O-methyl transferase activity has been found increased in schizophrenia and a functional polymorphism in the COMT gene itself has been associated with the disease, as well as with aggression in patients. We tested the hypothesis that COMT genotype for the functional Val158Met might contribute to the variance of self reported schizotypy and aggression scores in the normal population. We genotyped 379 healthy 18- to 24-year-old male individuals who had completed the PAS, SPQ and AQ questionnaires. Our results showed that self-reported schizotypy scores in both questionnaires were significantly related to COMT genotype (P = 0.028 for the PAS and P = 0.015 for the SPQ) with individuals homozygous for the high activity allele showing the highest scores. No significant differences were detected for AQ scores. We conclude that the COMT genotype for the functional Val158Met polymorphism is correlated to self-reported schizotypy in healthy males. This finding is in the same direction as reported findings on schizophrenia and it adds to the list of evidence that COMT or a nearby gene in linkage disequilibrium is involved in the pathogenesis of the disease.

Working memory and schizophrenia: evidence for slowed encoding

Previous studies have found impairments in working memory in individuals with schizophrenia, but have not identified the underlying information processing deficit. Because schizophrenia is associated with slowed cognitive processing, deficits on working memory tests may be due to decreased speed of encoding rather than an inability to maintain information over time. This hypothesis was examined using a Delayed Match to Sample (DMTS) Test. Task difficulty under 0-delay conditions was equated by individually establishing the stimulus presentation time needed to reach approximately 80% accuracy. Schizophrenia participants required longer presentation durations, but there were no group differences under delay conditions when performance was equated in the 0-delay condition. These results suggest that poor working memory performance in schizophrenia results from slowed encoding processes.

Prefrontal cortex dysfunction mediates deficits in working memory and prepotent responding in schizophrenia

BACKGROUND

Schizophrenic patients show deficits in working memory (WM) and inhibition of prepotent responses. We examined brain activity while subjects performed tasks that placed demands on WM and overriding prepotent response tendencies, testing predictions that both processes engage overlapping prefrontal cortical (PFC) regions and that schizophrenic patients show reduced PFC activity and performance deficits reflecting both processes.

METHODS

Functional magnetic resonance imaging data were acquired while 16 schizophrenic and 15 healthy subjects performed the N-Back task that varied WM load and a version of the AX-CPT that required overriding a prepotent response tendency.

RESULTS

Both tasks engaged overlapping cortical networks (e.g., bilateral dorsolateral PFC, Broca's area, parietal cortex). Increased WM load monotonically increased activity; preparation to override a prepotent response produced greater and more enduring activity. Group differences on each task emerged in a right dorsolateral PFC region: schizophrenic subjects showed lesser magnitude increases under conditions of high WM and prepotent response override demands, with concomitant performance impairments.

CONCLUSIONS

Schizophrenic patients exhibit PFC-mediated deficits in WM and preparation to override prepotent responses. Findings are consistent with the operation of a single underlying PFC-mediated cognitive control mechanism and with physiologic dysfunction of the dorsolateral PFC in schizophrenic patients reflecting impairments in this mechanism.

Prefrontal-posterior parietal networks in schizophrenia: primary dysfunctions and secondary compensations

BACKGROUND

Working memory (WM) deficits are well known in schizophrenia and have been associated with abnormal activation patterns of the prefrontal cortex (PFC) during cognitive performance. The magnitude and particularly the direction of the PFC activation -- i.e., increased (hyperfrontality) or decreased (hypofrontality) -- in schizophrenia, as well as its pathophysiological implications, remain controversial. Working memory is supported by a distributed neural network, whose main components are the PFC and the posterior parietal (PPC) cortices. Monkey studies indicate that, during WM performance, PFC functional lesions may be compensated by the PPC if task demands center mainly on anticipating responses, but not if they center on remembering cues. We hypothesized that a primarily dysfunctional PFC in schizophrenia might show hypofrontality or hyperfrontality as a result, respectively, of efficient or inefficient PPC compensation, as dictated by task demands. To test our proposition, we biased the demands of WM tasks toward anticipating responses or remembering cues and measured its impact on the PFC-PPC functional balance in a group of schizophrenic patients and one of normal control subjects.

METHODS

We used functional magnetic resonance imaging to measure correlates of neuronal activity in the PFC and PPC of schizophrenic patients and control subjects performing WM tasks that either demanded information retention or allowed for response anticipation.

RESULTS

When compared to control subjects, schizophrenic patients exhibited decreased PFC activation and increased PPC activation during anticipatory WM performance, and increased PFC activation during mnemonic WM performance.

CONCLUSIONS

In schizophrenia, a PFC dysfunction results in hypo- or hyperfrontality as a function of whether other alternate areas of a PFC-PPC network for WM are available and efficacious in supporting specific task demands.

Correlation between clinical syndromes and neuropsychological tasks in unmedicated patients with recent onset schizophrenia

The aim of this study is to circumscribe the cognitive deficits according to schizophrenic syndromes in a population of sub-acute untreated patients. We have studied the cross-sectional correlation between cognitive deficits and schizophrenic symptoms, in a group of 24 untreated patients (including 17 neuroleptic-naive patients) with recent onset of the disease. A task of alertness, a working memory (WM) test (including two levels of difficulty) and an abbreviated version of the Wisconsin Card Sorting Test (WCST) were selected. WM deficits and poor performance on the WCST were highly correlated with disorganized symptoms, modestly with the positive syndrome and not with the negative syndrome. Thus, disorganized symptoms, more than any other, appear to be related to the impairment of executive function and WM in recent onset unmedicated patients with schizophrenia.

Time course of inhibition and facilitation in patients with schizophrenia

INTRODUCTION

Negative priming (NP) paradigms have been used extensively to understand the nature and time course of inhibitory deficits in patient populations. A majority of these studies have reported abnormal NP effects, with patients showing faster reaction times on NP sequences compared to the slowing displayed by controls.

METHODS

A Stroop NP task was employed to measure immediate (within-trial) attentional processing as well as the sustainment (between-trial) of these processes in 12 medicated schizophrenia inpatients and 13 matched controls. Two response stimulus intervals (RSIs) were presented (500 ms and 2000 ms). Within-trial Stroop effects (interference and facilitation) and between-trial priming effects (negative and positive priming) were measured. Clinical symptomatology and duration of illness were also examined.

RESULTS

At short RSIs of 500 ms, chronically ill state hospital schizophrenia patients failed to exhibit NP. In contrast, the control subjects exhibited normal NP at the short RSI but this priming faded at the long 2000 ms RSI and was no longer significant. The facilitatory priming effects remained stable across time in both groups.

CONCLUSIONS

These results suggest that schizophrenia patients are better able to inhibit irrelevant stimuli that are immediate, but the sustainment of inhibition across very short time intervals (500 ms) may fade compared to controls.

Assessing the molecular genetics of attention networks

BACKGROUND

Current efforts to study the genetic underpinnings of higher brain functions have been lacking appropriate phenotypes to describe cognition. One of the problems is that many cognitive concepts for which there is a single word (e.g. attention) have been shown to be related to several anatomical networks. Recently, we have developed an Attention Network Test (ANT) that provides a separate measure for each of three anatomically defined attention networks.

RESULTS

In this study we have measured the efficiency of neural networks related to aspects of attention using the ANT in a population of 200 adult subjects. We then examined genetic polymorphisms in four candidate genes (DRD4, DAT, COMT and MAOA) that have been shown to contribute to the risk of developing various psychiatric disorders where attention is disrupted. We find modest associations of several polymorphisms with the efficiency of executive attention but not with overall performance measures such as reaction time.

CONCLUSIONS

These results suggest that genetic variation may underlie inter-subject variation in the efficiency of executive attention. This study also shows that genetic influences on executive attention may be specific to certain anatomical networks rather than affecting performance in a global or non-specific manner. Lastly, this study further validates the ANT as an endophenotypic assay suitable for assessing how genes influence certain anatomical networks that may be disrupted in various psychiatric disorders.

Layer-specific reductions in GFAP-reactive astroglia in the dorsolateral prefrontal cortex in schizophrenia

Neuroimaging studies have implicated the prefronto-striatal loop as a substrate for the cognitive deficits in schizophrenia (SCHZ). Postmortem morphometric studies reveal that layers III and V of the dorsolateral prefrontal cortex (dlPFC), which gave rise to glutamatergic projections to neostriatum, demonstrate the most structural pathology in this region of the SCHZ. These neuronal alterations in SCHZ are not accompanied by marked glial changes as revealed by Nissl staining. We examined the glial-type specific pathology in SCHZ by analyzing the glial fibrillary acidic protein- (GFAP) immunoreactive astroglia in contrast to the Nissl-stained general pool of glial cells in dlPFC (area 9) from 9 subjects with SCHZ and 15 psychiatrically normal control subjects. In layer V of the dlPFC in SCHZ, there was a significant 32% reduction in the GFAP-area fraction, 81% increase in the density of the GFAP-positive cell bodies and a 14% decrease in the width of the cortical layer V, as compared to the control subjects. None of these parameters were affected in layers III and IV in the SCHZ. Therefore, only subtle, type- and layer-specific glial pathology is present in the dlPFC in SCHZ. Astroglial pathology in dlPFC may reflect disturbances of the neuron-glia interactions in layer V and may be related to the dysfunctional prefronto-striatal circuits, dopaminergic alterations and cognitive pathology in SCHZ.

The neurobiology of apolipoproteins in psychiatric disorders

A genetic contribution to the transmission of psychiatric disorders has been established and it is now accepted that several genes confer susceptibility to schizophrenia, and similar disorders, giving rise to a complex polygenic mode of inheritance. With the high-throughput molecular profiling techniques available, apolipoproteins have emerged as being important factors in psychiatric disorders. This review will focus on three apolipoproteins that have recently been shown to be elevated in neuropsychiatric disorders: apoD, apoE, and apoL. Furthermore, the authors discuss the role of apoD in the pathology and pharmacotherapy of schizophrenia and bipolar disorder.

The cognitive neuropsychiatric approach to investigating the neurobiology of schizophrenia and other disorders

In this paper, we examine a cognitive neuropsychiatric approach to understanding neuropsychiatric disorders by examining recent data in schizophrenia. By understanding and applying this approach, we suggest that the processes underlying the neurobiology of a range of other psychiatric disorders can be understood. Further, an assessment of the brain-behaviour relationships through this emerging discipline provides testable models for further study, using a range of techniques including functional and other imaging techniques.

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.

Effects on the brain of a psychological treatment: cognitive remediation therapy: functional magnetic resonance imaging in schizophrenia

BACKGROUND

The results of one randomised control trial testing a psychological rehabilitation programme aimed at information processing strategies showed improvements in cognition post-treatment.

AIMS

To determine whether there are concomitant brain activation changes as a result of engaging in cognitive remediation therapy (CRT).

METHOD

Three groups (patients receiving control therapy or CRT and a healthy control group) were investigated in a repeated measures design using the two-back test. Functional magnetic resonance imaging (fMRI) data and a broad assessment of executive functioning were completed at baseline and post-treatment. Brain activation changes were identified after accounting for possible task-correlated motion artefact.

RESULTS

fMRI analyses indicate that the control group showed decreased activation but the two patient groups showed an increase in activation over time. The patient group that received successful CRT had significantly increased brain activation in regions associated with working memory, particularly the frontocortical areas.

CONCLUSIONS

This is the first time that brain activation changes in a seriously disabled group of patients with schizophrenia can be associated clearly with psychological rather than pharmacological therapy.

Prefrontal dopamine D1 receptors and working memory in schizophrenia

Studies in nonhuman primates documented that appropriate stimulation of dopamine (DA) D1 receptors in the dorsolateral prefrontal cortex (DLPFC) is critical for working memory processing. The defective ability of patients with schizophrenia at working memory tasks is a core feature of this illness. It has been postulated that this impairment relates to a deficiency in mesocortical DA function. In this study, D1 receptor availability was measured with positron emission tomography and the selective D1 receptor antagonist [11C]NNC 112 in 16 patients with schizophrenia (seven drug-naive and nine drug-free patients) and 16 matched healthy controls. [11C]NNC 112 binding potential (BP) was significantly elevated in the DLPFC of patients with schizophrenia (1.63 +/- 0.39 ml/gm) compared with control subjects (1.27 +/- 0.44 ml/gm; p = 0.02). In patients with schizophrenia, increased DLPFC [11C]NNC 112 BP was a strong predictor of poor performance at the n-back task, a test of working memory. These findings confirm that alteration of DLPFC D1 receptor transmission is involved in working memory deficits presented by patients with schizophrenia. Increased D1 receptor availability observed in patients with schizophrenia might represent a compensatory (but ineffective) upregulation secondary to sustained deficiency in mesocortical DA function.

Functional neuroimaging in neurology and psychiatry

How can functional neuroimaging be applied to clinical neurology and psychiatry? This article reviews selected contributions of functional neuroimaging to the clinical neurosciences. We review selected technical aspects of positron emission tomography, single photon emission tomography, and functional magnetic resonance imaging with a focus on the relative strengths and weaknesses of these techniques. Consumers of functional neuroimaging research are encouraged to consider the limitations of imaging techniques and theoretical pitfalls of cognitive task design when interpreting results of functional imaging studies. Then, we selectively review the contributions of functional neuroimaging to neurology and psychiatry, including the areas of epilepsy, stroke, chronic pain, schizophrenia, depression, and obsessive-compulsive disorder. Future directions of functional neuroimaging research are offered, with the emphasis that the best conclusions are informed by a convergence of research from functional neuroimaging, neurophysiological, and lesion studies.

Could the hypofrontality pattern in schizophrenia be modified through neuropsychological rehabilitation?

OBJECTIVE

The effects of neuropsychological treatment on cognitive hypofrontality were examined in schizophrenic patients through the score activation.

METHOD

Eight subjects (six men and two women) with persistent negative symptoms and cognitive impairments were evaluated with single photon emission computed tomography (SPECT) procedures and neuropsychological battery before and after a neuropsychological treatment group.

RESULTS

After treatment an enhancement in neuropsychological performance was found, especially in executive functions. The activation score showed an increase over baseline levels and no cognitive-dependent hypofrontality after treatment was found. Although the prefrontal blood flow changes were small and non-specific, they suggest a reduction of the cognitive hypofrontality after neuropsychological treatment.

CONCLUSION

Cognitive improvements after neuropsychological treatment would possibly be related with the diminution of the functional hypoactivity in the prefrontal areas.

De-coupling of cognitive performance and cerebral functional response during working memory in schizophrenia

Working memory dysfunction is considered to be fundamental to the cognitive and clinical features evident in schizophrenia. Functional neuroimaging studies have begun to elucidate the neurobiological basis of such deficits, however, interpretation of these studies may be confounded by performance impairment, when the cognitive load exceeds the limited response capacity of patients with schizophrenia. In this study, patients were pre-selected on the basis of intact performance on a relatively low-load verbal working memory task, in order to mitigate against performance confounds. Subjects included 20 right-handed male subjects with chronic schizophrenia, and 20 right-handed, age-matched, male healthy controls, without personal or familial psychiatric history. All subjects underwent fMRI scanning whilst performing a verbal n-back task. There were no significant between-group differences in target identification; the patient group showed a significantly increased mean response latency. Both groups demonstrated robust fronto-parietal activation. In the control subjects, the power of functional response was positively correlated with reaction time in bilateral posterior parietal cortex, however, this coupling of behavioural performance and cerebral response was not evident in the patients. This deficit, apparent within the performance capacity of the patients, may represent a fundamental abnormality in schizophrenia, and may compromise performance at higher cognitive loads.

Determination of regional cerebral function with FDG-PET imaging in neuropsychiatric disorders

Functional brain imaging using 18F fluorodeoxyglucose (FDG) and positron emission tomography (PET) has greatly enhanced our understanding of brain function both in normal conditions as well as in a wide variety of neuropsychiatric disorders. We review the uses of FDG PET in the diagnosis, management, and follow-up of patients with neuropsychiatric disorders. This article will also explore what FDG-PET imaging has revealed in these neuropsychiatric disorders and how these findings relate to both research and clinical applications.

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.

P300 asymmetry in schizophrenia: a meta-analysis

P300 event-related brain potential (ERP) amplitude is smaller in patients with schizophrenia compared to unaffected controls, but whether left temporal component amplitude is also smaller is debated. The present study employed meta-analytical methods to quantitatively assess previous P300 schizophrenia asymmetry findings. All P300 articles on schizophrenia using an auditory oddball paradigm published before January 2000 were obtained by comprehensive literature searches and cross-referencing for related articles. A total of 19 original articles reporting complete midline electrode data and 11 articles reporting lateral asymmetry electrode data were reviewed, which included different independent conditions that yielded 50 independent data sets. P300 amplitude differences between patients with schizophrenia and control subjects from the midline electrodes yielded effect sizes that differed among recording sites, such that Fz was significantly smaller than Pz, with Cz effect sizes smaller than Pz but larger than Fz. Comparison of P300 amplitude from the lateral data for the T3 and T4 electrodes found no reliable effect size difference when these electrodes were analyzed separately. However, comparison of P300 amplitude effect sizes from the TCP1 was significantly larger than that from the TCP2 when these electrodes were analyzed separately. P300 amplitude is smaller overall in patients with schizophrenia compared to control subjects and differs in its effect size topography across the midline and temporal electrode sites, with the strongest effect sizes obtained for the Pz midline and TCP1 lateral electrodes.

Anticipating incoming events: an impaired cognitive process in schizophrenia

Intentions are central to guiding actions to their completion because they generate expectations which precede the realization of a task. This ability to manage time was investigated by using a cognitive task which involves several highly integrated processes: sequential learning, explicit processing, and working memory. In this task, participants are required to explicitly learn a repeating color sequence before receiving an instruction to give an anticipatory motor response concerning the next element. Two types of sequences (temporal and spatial) and three experimental conditions were tested in both a group of normal participants and a group of schizophrenic patients. Schizophrenics were included because their condition is known to alter conscious executive function. Our results showed that schizophrenic patients have a strong deficit in performing anticipation tasks. Although they learned the sequences almost normally, their anticipatory ability was reduced in comparison to normal participants in all the tested conditions. These results expand the notion of a working memory deficit in schizophrenia and bear strong implications for understanding executive disorders observed in such patients.

Assessing the heritability of attentional networks

BACKGROUND

Current efforts to study the genetics of higher functions have been lacking appropriate phenotypes to describe cognition. One of the problems is that many cognitive concepts for which there is a single word (e.g. attention) have been shown to be related to several anatomical networks. Recently we have developed an Attention Network Test (ANT) that provides a separate measure for each of three anatomically defined attention networks. In this small scale study, we ran 26 pairs of MZ and DZ twins in an effort to determine if any of these networks show sufficient evidence of heritability to warrant further exploration of their genetic basis.

RESULTS

The efficiency of the executive attention network, that mediates stimulus and response conflict, shows sufficient heritability to warrant further study. Alerting and overall reaction time show some evidence for heritability and in our study the orienting network shows no evidence of heritability.

CONCLUSIONS

These results suggest that genetic variation contributes to normal individual differences in higher order executive attention involving dopamine rich frontal areas including the anterior cingulate. At least the executive portion of the ANT may serve as a valid endophenotype for larger twin studies and subsequent molecular genetic analysis in normal subject populations.

Effect of schizophrenia on frontotemporal activity during word encoding and recognition: a PET cerebral blood flow study

OBJECTIVE

Neuropsychological studies have shown that deficits in verbal episodic memory in schizophrenia occur primarily during encoding and retrieval stages of information processing. The current study used positron emission tomography to examine the effect of schizophrenia on change in cerebral blood flow (CBF) during these memory stages.

METHOD

CBF was measured in 23 healthy comparison subjects and 23 patients with schizophrenia during four conditions: resting baseline, motor baseline, word encoding, and word recognition. The motor baseline was used as a reference that was subtracted from encoding and recognition conditions by using statistical parametric mapping.

RESULTS

Patients' performance was similar to that of healthy comparison subjects. During word encoding, patients showed reduced activation of left prefrontal and superior temporal regions. Reduced left prefrontal activation in patients was also seen during word recognition, and additional differences were found in the left anterior cingulate, left mesial temporal lobe, and right thalamus. Although patients' performance was similar to that of healthy comparison subjects, left inferior prefrontal activation was associated with better performance only in the comparison subjects.

CONCLUSIONS

Left frontotemporal activation during episodic encoding and retrieval, which is associated with better recognition in healthy people, is disrupted in schizophrenia despite relatively intact recognition performance and right prefrontal function. This may reflect impaired strategic use of semantic information to organize encoding and facilitate retrieval.

Effect of COMT Val108/158 Met genotype on frontal lobe function and risk for schizophrenia

Abnormalities of prefrontal cortical function are prominent features of schizophrenia and have been associated with genetic risk, suggesting that susceptibility genes for schizophrenia may impact on the molecular mechanisms of prefrontal function. A potential susceptibility mechanism involves regulation of prefrontal dopamine, which modulates the response of prefrontal neurons during working memory. We examined the relationship of a common functional polymorphism (Val(108/158) Met) in the catechol-O-methyltransferase (COMT) gene, which accounts for a 4-fold variation in enzyme activity and dopamine catabolism, with both prefrontally mediated cognition and prefrontal cortical physiology. In 175 patients with schizophrenia, 219 unaffected siblings, and 55 controls, COMT genotype was related in allele dosage fashion to performance on the Wisconsin Card Sorting Test of executive cognition and explained 4% of variance (P = 0.001) in frequency of perseverative errors. Consistent with other evidence that dopamine enhances prefrontal neuronal function, the load of the low-activity Met allele predicted enhanced cognitive performance. We then examined the effect of COMT genotype on prefrontal physiology during a working memory task in three separate subgroups (n = 11-16) assayed with functional MRI. Met allele load consistently predicted a more efficient physiological response in prefrontal cortex. Finally, in a family-based association analysis of 104 trios, we found a significant increase in transmission of the Val allele to the schizophrenic offspring. These data suggest that the COMT Val allele, because it increases prefrontal dopamine catabolism, impairs prefrontal cognition and physiology, and by this mechanism slightly increases risk for schizophrenia.

The neuropsychology and neuroanatomy of bipolar affective disorder: a critical review

Bearden CE, Hoffman KM, Cannon TD. The neuropsychology and neuroanatomy of bipolar affective disorder: a critical review. Bipolar Disord 2001: 3: 106 150. C Munksgaard, 2001

OBJECTIVES

To present a comprehensive review of the existing neuropsychological and neuroimaging literature on bipolar affective disorder. This review critically evaluates two common conceptions regarding the neuropsychology of bipolar disorder: 1) that, in contrast to schizophrenia, bipolar affective disorder is not associated with general cognitive impairment independent of illness episodes, and 2) relative right hemisphere (RH) dysfunction is implicated in bipolar illness patients, supported by reports of relatively greater impairment in visuospatial functioning, lateralization abnormalities, and mania secondary to RH lesions.

METHODS

The major computerized databases (Medline and PSYCInfo) were consulted in order to conduct a comprehensive, integrated review of the literature on the neuropsychology and neuroanatomy of bipolar disorder. Articles meeting specified criteria were included in this review.

RESULTS

In a critical evaluation of the above notions, this paper determines that: 1) while there is little evidence for selective RH dysfunction, significant cognitive impairment may be present in bipolar illness, particularly in a subgroup of chronic, elderly or multiple-episode patients, suggesting a possible toxic disease process, and 2) the underlying functional correlate of these cognitive deficits may be white matter lesions ('signal hyperintensities') in the frontal lobes and basal ganglia, regions critical for executive function, attention, speeded information processing, learning and memory, and affect regulation. While this hypothesized neural correlate of cognitive impairment in bipolar disorder is speculative, preliminary functional neuroimaging evidence supports the notion of frontal and subcortical hypometabolism in bipolar illness.

CONCLUSIONS

The etiology of the structural brain abnormalities commonly seen in bipolar illness, and their corresponding functional deficits, remains unknown. It is possible that neurodevelopmental anomalies may play a role, and it remains to be determined whether there is also some pathophysiological progression that occurs with repeated illness episodes. More research is needed on first-episode patients, relatives of bipolar probands, and within prospective longitudinal paradigms in order to isolate disease-specific impairments and genetic markers of neurocognitive function in bipolar disorder.

Current perspectives on the pathophysiology of schizophrenia, depression, and anxiety disorders

This article reviews the rapidly changing concepts related to the pathophysiology of major psychiatric disorders. The current era is an exciting one for psychiatric research and the rapidity with which advances are being made is a source of hope to patients with these disorders and for society.

Neuropsychological frontal lobe tests indicate that bipolar depressed patients are more impaired than unipolar

OBJECTIVES

The aim of this study was to compare the neuropsychological performance of patients with bipolar or unipolar mood disorders during acute episodes of depression using intelligence and frontal lobe tests.

METHODS

Fifteen patients with bipolar depression (BP) and 30 with unipolar depression (UP) were studied. For the neuropsychological assessment, the following tests: the Wechsler Adult Intelligence Scale-Revised (WAIS-R), the Trail Making Test (TMT), the Stroop test, the verbal fluency test and the Wisconsin Card Sorting Test (WCST) were used.

RESULTS

The mean intensity of depression and mean duration of illness were similar in both groups. Patients in the BP group achieved significantly lower levels of performance in the non-verbal part of WAIS-R, in both parts of the Stroop test, in the verbal fluency test and also showed a tendency to achieve poorer results in TMT-B than those in the UP group. Bipolar depressed patients also produced significantly poorer results with the WCST as they made twice as many perseverative errors and only completed half of the correct categories compared with the UP patients. The results of the TMT-A tests, which measure psychomotor slowness, were similar in BP and UP patients. No differences between the results of male and female patients were noted in either group. Deterioration of the results associated with duration of the illness was only observed in the UP patients.

CONCLUSIONS

A higher degree of cognitive dysfunction connected with frontal lobe activity during an acute depressive episode was found in bipolar compared with unipolar depressed patients. These results may corroborate other findings pointing to pathogenic distinctions between bipolar and unipolar affective illness and to some similarities between bipolar illness and schizophrenia.

Increased CNS levels of apolipoprotein D in schizophrenic and bipolar subjects: implications for the pathophysiology of psychiatric disorders

Chronic administration of the atypical antipsychotic drug, clozapine, to rodents has been shown to increase the concentration of apolipoprotein D (apoD) in several area of the brain, suggesting that apoD could be involved in the therapeutic effects of antipsychotic drugs and/or the pathology of psychotic illnesses. Here, we measured a significant decrease in the concentration of apoD in serum samples from schizophrenic patients. In contrast, apoD levels were significantly increased (92--287%) in dorsolateral prefrontal cortex (Brodmann's area 9) of schizophrenic and bipolar subjects. Elevated levels of apoD expression were also observed in the caudate of schizophrenic and bipolar subjects (68--89%). No differences in apoD immunoreactivity were detected in occipital cortex (Brodmann's area 18) in either group, or in the hippocampus, substantia nigra, or cerebellum of the schizophrenic group. The low serum concentrations of apoD observed in these patients supports recent hypotheses involving systemic insufficiencies in lipid metabolism/signaling in schizophrenia. Elevation of apoD expression selectively within central nervous system regions implicated in the pathology of these neuropsychiatric disorders suggests a focal compensatory response that neuroleptic drug regimens may augment.

Event-Related Brain Potentials and Central Executive Function: Further Evidence for Baddeley's Model

Baddeley's influential model of working memory postulates a unitary central executive that allocates mental resources to several distinct short-term buffers. Subjects viewed individually presented single numerals and were required to maintain memory sets comprised of the most recently represented three stimuli. A clearly discernible visual event-related potentials (ERP) component emerged once the lengths of series of individual numbers exceeded memory set size and revision of working memory contents was required. An ERP correlate of working memory revision also emerged upon updating of auditory stimuli. This component was absent when subjects were exposed to the same series of stimuli in a standard “oddball” target detection situation. ERPs elicited when subjects were given the opportunity to rehearse without the need to update working memory contents clearly differed in latency from ERPs seen during updating. These findings provide support for previous studies suggesting a specific ERP correlate of central executive processes in working memory and are consistent with Baddeley's model.

Functional neuroanatomy of auditory working memory in schizophrenia: relation to positive and negative symptoms

Functional brain imaging studies of working memory (WM) in schizophrenia have yielded inconsistent results regarding deficits in the dorsolateral prefrontal (DLPFC) and parietal cortices. In spite of its potential importance in schizophrenia, there have been few investigations of WM deficits using auditory stimuli and no functional imaging studies have attempted to relate brain activation during auditory WM to positive and negative symptoms of schizophrenia. We used a two-back auditory WM paradigm in a functional MRI study of men with schizophrenia (N = 11) and controls (N = 13). Region of interest analysis was used to investigate group differences in activation as well as correlations with symptom scores from the Brief Psychiatric Rating Scale. Patients with schizophrenia performed significantly worse and were slower than control subjects in the WM task. Patients also showed decreased lateralization of activation and significant WM related activation deficits in the left and right DLPFC, frontal operculum, inferior parietal, and superior parietal cortex but not in the anterior cingulate or superior temporal gyrus. These results indicate that in addition to the prefrontal cortex, parietal cortex function is also disrupted during WM in schizophrenia. Withdrawal-retardation symptom scores were inversely correlated with frontal operculum activation. Thinking disturbance symptom scores were inversely correlated with right DLPFC activation. Our findings suggest an association between thinking disturbance symptoms, particularly unusual thought content, and disrupted WM processing in schizophrenia.