The cognitive neuroscience of working memory: relevance to CNTRICS and schizophrenia

Glycine transporter 1 as a potential therapeutic target for schizophrenia-related symptoms: evidence from genetically modified mouse models and pharmacological inhibition

Schizophrenia is characterized by positive symptoms such as hallucinations, negative symptoms such as blunted affect, and symptoms of cognitive deficiency such as deficits in working memory and selective attention. N-methyl-d-aspartate receptor (NMDAR) hypofunction has been implicated in all three pathophysiological aspects of the disease. Due to the severe side effects of direct NMDAR agonists, targeting the modulatory co-agonist glycine-B site of the NMDAR is considered to be a promising strategy to ameliorate NMDAR hypofunction. To assess the antipsychotic and pro-cognitive potential of this approach, we examine the strategies designed to enhance glycine-B site occupancy through glycine transporter 1 (GlyT1) blockade. Among the existing transgenic mouse models with GlyT1 deficits, the one specifically targeting forebrain neuronal GlyT1 has yielded the most promising data on cognitive enhancement. Parallel advances in the pharmacology of GlyT1 inhibition point not only to an enhancement of attention, learning and memory but also include suggestions of mood enhancing effects that might be valuable for treating negative symptoms. Thus, interventions at GlyT1 are highly effective in modifying multiple brain functions, and dissection of their respective mechanisms is expected to further maximize their therapeutic potential for human mental diseases.

Working memory for vibrotactile frequencies: comparison of cortical activity in blind and sighted individuals

In blind, occipital cortex showed robust activation to nonvisual stimuli in many prior functional neuroimaging studies. The cognitive processes represented by these activations are not fully determined, although a verbal recognition memory role has been demonstrated. In congenitally blind and sighted (10 per group), we contrasted responses to a vibrotactile one-back frequency retention task with 5-s delays and a vibrotactile amplitude-change task; both tasks involved the same vibration parameters. The one-back paradigm required continuous updating for working memory (WM). Findings in both groups confirmed roles in WM for right hemisphere dorsolateral prefrontal (DLPFC) and dorsal/ventral attention components of posterior parietal cortex. Negative findings in bilateral ventrolateral prefrontal cortex suggested task performance without subvocalization. In bilateral occipital cortex, blind showed comparable positive responses to both tasks, whereas WM evoked large negative responses in sighted. Greater utilization of attention resources in blind were suggested as causing larger responses in dorsal and ventral attention systems, right DLPFC, and persistent responses across delays between trials in somatosensory and premotor cortex. In sighted, responses in somatosensory and premotor areas showed iterated peaks matched to stimulation trial intervals. The findings in occipital cortex of blind suggest that tactile activations do not represent cognitive operations for nonverbal WM task. However, these data suggest a role in sensory processing for tactile information in blind that parallels a similar contribution for visual stimuli in occipital cortex of sighted.

Investigating the Role of Current Strength in tDCS Modulation of Working Memory Performance in Healthy Controls

Transcranial direct current stimulation (tDCS) is a brain stimulation technique that has the potential to improve working memory (WM) deficits in many clinical disorders. The aim of this study was to investigate the role of current strength on the ability of anodal tDCS to improve WM, and secondly to investigate the time course of effects. Twelve healthy participants underwent three stimulation sessions consisting of 20 min of either 1 mA anodal tDCS, 2 mA anodal tDCS, or sham tDCS to the left dorsolateral prefrontal cortex (DLPFC) localized via F3, all whilst completing a WM task. Intra-stimulation and post-stimulation WM performances were measured using the n-back and Sternberg tasks respectively. Results revealed no significant improvements in participants' accuracy, but a significant interaction was found with respect to current strength and time for accurate reaction time. The finding provides partial support for the hypothesis, in that it appears current strength may affect aspects of WM performance. However, more research is needed, and a higher difficulty level of WM tasks is one of the suggestions discussed for future research.

Functional magnetic resonance imaging of a parametric working memory task in schizophrenia: relationship with performance and effects of antipsychotic treatment

RATIONALE

Working memory dysfunction is frequently observed in schizophrenia. The neural mechanisms underlying this dysfunction remain unclear, with functional neuroimaging studies reporting increased, decreased or unchanged activation compared to controls.

OBJECTIVES

We investigated the neural correlates of spatial working memory in schizophrenia with particular consideration of effects of antipsychotic treatment and relation to performance levels in the patient group.

METHOD

We used functional magnetic resonance imaging and studied the blood-oxygen-level-dependent (BOLD) response of 45 schizophrenia outpatients and 19 healthy controls during a parametric spatial n-back task.

RESULTS

Performance in both groups deteriorated with increasing memory load (0-back, 1-back, 2-back), but the two groups did not significantly differ in performance overall or as a function of load. Patients produced stronger BOLD signal in occipital and lateral prefrontal cortex during task performance than controls. This difference increased with increasing working memory load in the prefrontal areas. We also found that in patients with good task performance, the BOLD response in left prefrontal cortex showed a stronger parametric increase with working memory load than in patients with poor performance. Second-generation antipsychotics were independently associated with left prefrontal BOLD increase in response to working memory load, whereas first-generation antipsychotics were associated with BOLD decrease with increasing load in this area.

CONCLUSIONS

Together, these findings suggest that in schizophrenia patients, normal working memory task performance may be achieved through compensatory neural activity, especially in well-performing patients and in those treated with second-generation antipsychotics.

Impaired spatial working memory maintenance in schizophrenia involves both spatial coordinates and spatial reference frames

Spatial working memory (SWM) dysfunction is a central finding in schizophrenia; however, more evidence of impaired maintenance over time is required. Consequently, the present study examined SWM maintenance over short unfilled delays, and with encoding equated. The influence of a vertical reference frame to support maintenance was also investigated. The performance of 58 patients with schizophrenia and 50 healthy controls was assessed using the Visuo-Spatial Working Memory (VSWM) Test across three unfilled delays (0, 2, and 4s). Inaccuracy of direction and distance responses was examined at each delay duration. The results showed that performance was significantly less accurate for both distance and direction responses at 2 and 4s delays in schizophrenia, but was not significantly different from controls at the 0s delay. Patients showed a particularly marked loss of accuracy between the time interval of 0-2s. Furthermore, schizophrenia participants exhibited significantly greater response variability at the vertical axis of symmetry than controls at the 2 and 4s delays, but not at the 0s delay. These data clearly show both impaired maintenance over time and difficulty using a vertical frame of reference in schizophrenia. The latter findings may reflect, in part, dysfunctional reference-related inhibition.

Cortical kynurenic acid bi-directionally modulates prefrontal glutamate levels as assessed by microdialysis and rapid electrochemistry

Using two in vivo methods, microdialysis and rapid in situ electrochemistry, this study examined the modulation of extracellular glutamate levels by endogenously produced kynurenic acid (KYNA) in the prefrontal cortex (PFC) of awake rats. Measured by microdialysis, i.p. administration of KYNA's bioprecursor L-kynurenine dose-dependently elevated extracellular KYNA and reduced extracellular glutamate (nadir after 50 mg/kg kynurenine: 60% decrease from baseline values). This dose-dependent decrease in glutamate levels was also seen using a glutamate-sensitive microelectrode array (MEA) (31% decrease following 50 mg/kg kynurenine). The kynurenine-induced reduction in glutamate was blocked (microdialysis) or attenuated (MEA) by co-administration of galantamine (3 mg/kg i.p.), a drug that competes with KYNA at an allosteric potentiating site of the alpha 7 nicotinic acetylcholine receptor. In separate experiments, extracellular glutamate levels were measured by MEA following the local perfusion (45 min) of the PFC with kynurenine (2.5 microM) or the selective KYNA biosynthesis inhibitor S-ethylsulfonylbenzoylalanine (S-ESBA; 5 mM). In agreement with previous microdialysis studies, local kynurenine application produced a reversible reduction in glutamate (nadir: -29%), whereas perfusion with S-ESBA increased glutamate levels reversibly (maximum: +38%). Collectively, these results demonstrate that fluctuations in the biosynthesis of KYNA in the PFC bi-directionally modulate extracellular glutamate levels, and that qualitatively very similar data are obtained by microdialysis and MEA. Since KYNA levels are elevated in the PFC of individuals with schizophrenia, and since prefrontal glutamatergic and nicotinic transmission mediate cognitive flexibility, normalization of KYNA levels in the PFC may constitute an effective treatment strategy for alleviating cognitive deficits in schizophrenia.

The Association between Dopamine DRD2 Polymorphisms and Working Memory Capacity Is Modulated by a Functional Polymorphism on the Nicotinic Receptor Gene CHRNA4

Working memory capacity is extremely limited and individual differences are heritable to a considerable extent. In the search for a better understanding of the exact genetic underpinnings of working memory, most research has focused on functional gene variants involved in the metabolism of the neurotransmitter dopamine. Recently, there has been investigation of genes related to other neurotransmitter systems such as acetylcholine. The potential relevance of a polymorphism located in the gene coding for the alpha4 subunit of the nicotinic acetylcholine receptor (rs#1044396) has been discussed with respect to working memory, but empirical investigations have provided mixed results. However, pharmacological studies in both rodents and humans have shown that the effect of nicotinic agonists on cognitive functions is mediated by dopamine. We therefore hypothesized that such an interaction can be found on a molecular genetic level as well. In order to test this hypothesis, we genotyped 101 healthy subjects for rs#1044396 and three functional polymorphisms on the dopamine d2 receptor gene (rs#1800497, rs#6277, rs#2283265). These subjects performed a visuospatial working memory task in which memory load was systematically varied. We found a significant interaction between rs#1044396 and a haplotype block covering all three dopaminergic polymorphisms on working memory capacity. This effect only became apparent on higher levels of working memory load. This is the first evidence from a molecular genetic perspective that these two neurotransmitter systems interact on cognitive functioning. The results are discussed with regard to their implication for working memory theories and their clinical relevance for treatment of substance abuse and schizophrenia.

Language in schizophrenia Part 1: an Introduction

This is the first of two articles that discuss higher-order language and semantic processing in schizophrenia. This article reviews clinical characterizations of language output and the phenomenon of positive thought disorder, as well as more principled characterizations of language output in schizophrenia. It also gives an overview of evidence for the predominant theory of language dysfunction in schizophrenia: that it arises from abnormalities in (a) semantic memory and/or (b) working memory and executive function. The companion article (Part 2) focuses on the study of language in schizophrenia using online psycholinguistic methods and considers how the study of schizophrenia may inform our understanding of normal language processing.

Sexual dimorphism of spatial working memory profiles in schizophrenia

INTRODUCTION

The aim of the present study was to compare spatial working memory performance of females and males schizophrenia patients to verify whether the sexual dimorphism of spatial abilities present in the general population is found also in schizophrenia.

METHODS

We analysed different types of errors committed by each gender on the spatial working memory test of the Cambridge Neuropsychological Test Automated Battery to determine potential differences between them.

RESULTS

Despite the lack of difference in the number of errors between men and women, different profiles of errors were associated with the strategy used according to gender. The men's strategy was better compared to women. Specifically, for women strategy score correlated positively with searches in previously visited boxes, whereas for men it correlated with both previously visited boxes and never visited ones. However, men's strategy is more impaired by the number of revisits in boxes in which tokens have previously been found than female's one.

CONCLUSIONS

These results suggested impaired either central executive and/or visuospatial sketchpad of working memory in patients with schizophrenia. We demonstrated also that the worsening of strategy in men is principally due to central executive deficits compared to women with schizophrenia. The study of sex differences in cognitive performances could help in delineating partially different endophenotypes of schizophrenia in men and women.

Use of an acute challenge with d-amphetamine to model cognitive improvement in chronic schizophrenia

There is general agreement that pharmacologic improvement of cognition in chronic schizophrenia is a worthwhile therapeutic goal. Accordingly, there has been careful consideration about how neuropsychological methods can be used to detect improvement in cognition in people with schizophrenia. However, little data are available on the nature and magnitude of cognitive improvement that can occur with adjunctive therapeutic interventions.This double-blind, placebo-controlled crossover study examined the nature and magnitude of cognitive enhancement associated with a single-dose administration of d-amphetamine in 32 adult men with schizophrenia using a set of tasks developed specifically for detecting treatment-related change in cognitive function. Relative to placebo, acute d-amphetamine administration was associated with clinically meaningful improvement on measures of executive function and visual attention and vigilance, and with modest improvements on a measure of speed of processing. These results suggest that a brief computerized cognitive test battery designed for repeat administration, in combination with a statistical approach that emphasizes individual-level change, provides a sensitive approach to detecting the effect of cognitive-enhancing medications in people with chronic schizophrenia.

Switching schizophrenia patients from typical neuroleptics to aripiprazole: effects on working memory dependent functional activation

BACKGROUND

Deficits in working memory (WM) are a core symptom of schizophrenia patients and have been linked to dysfunctional prefrontal activation, which might be caused by a mesocortical hypodopaminergic state. Aripiprazole--a partial dopamine antagonist--is a novel antipsychotic, which increases frontal dopamine concentrations in preclinical studies. However, little is known about specific medication effects on the modulation of frontal activation during WM performance.

METHODS

We measured BOLD-response during a WM task in a longitudinal fMRI-study in eleven schizophrenia patients first when they received conventional antipsychotics (T1) and a second time after they had been switched to aripiprazole (T2). A healthy control group matched for age, handedness and gender was investigated at two corresponding time points. Data was analyzed with SPM5 in a 2 x 2 x 2 design (groupxsessionxtask).

RESULTS

Schizophrenia patients showed fewer correct responses compared to healthy controls at T1 and a trend-wise normalization at T2. The task activated the fronto-parietal network during the contrast 2-back>0-back in all participants. At T1 patients revealed a hypoactivation in the dorsal anterior cingulate cortex (ACC), which normalized after switch to aripiprazole and correlated with improved task performance. This was due to a significant increase in the patients group while the control group did not change, as corroborated by a significant groupxtime interaction in this region.

CONCLUSIONS

This study showed for the first time that the partial dopamine antagonist aripiprazole increases BOLD-signal during a WM task in the cognitive part of the ACC in schizophrenia patients, which may reflect its beneficial effect on cognitive deficits.

Cognition in mouse models of schizophrenia susceptibility genes

Cognitive deficits are core features of psychiatric disorders and contribute substantially to functional outcome. It is still unclear, however, how cognitive deficits are related to underlying genetic liability and overt clinical symptoms. Fortunately, animal models of susceptibility genes can illuminate how the products of disease-associated genetic variants affect brain function and ultimately alter behavior. Using as a reference findings from the Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia program and the SchizophreniaGene database, we review cognitive data from mutant models of rare and common genetic variants associated with schizophrenia.

Alterations in functional activation in euthymic bipolar disorder and schizophrenia during a working memory task

Dysfunctions in prefrontal cortical networks are thought to underlie working memory (WM) impairments consistently observed in both subjects with bipolar disorder and schizophrenia. It remains unclear, however, whether patterns of WM-related hemodynamic responses are similar in bipolar and schizophrenia subjects compared to controls. We used fMRI to investigate differences in blood oxygen level dependent activation during a WM task in 21 patients with euthymic bipolar I, 20 patients with schizophrenia, and 38 healthy controls. Subjects were presented with four stimuli (abstract designs) followed by a fifth stimulus and required to recall whether the last stimulus was among the four presented previously. Task-related brain activity was compared within and across groups. All groups activated prefrontal cortex (PFC), primary and supplementary motor cortex, and visual cortex during the WM task. There were no significant differences in PFC activation between controls and euthymic bipolar subjects, but controls exhibited significantly increased activation (cluster-corrected P < 0.05) compared to patients with schizophrenia in prefrontal regions including dorsolateral prefrontal cortex (DLPFC). Although the bipolar group exhibited intermediate percent signal change in a functionally defined DLPFC region of interest with respect to the schizophrenia and control groups, effects remained significant only between patients with schizophrenia and controls. Schizophrenia and bipolar disorder may share some behavioral, diagnostic, and genetic features. Differences in the patterns of WM-related brain activity across groups, however, suggest some diagnostic specificity. Both patient groups showed some regional task-related hypoactivation compared to controls across the brain. Within DLPFC specifically, patients with schizophrenia exhibited more severe WM-related dysfunction than bipolar subjects.

Patients with schizophrenia show deficits of working memory maintenance components in circuit-specific tasks

Working memory (WM) deficits are a neuropsychological core finding in patients with schizophrenia and also supposed to be a potential endophenotype of schizophrenia. Yet, there is a large heterogeneity between different WM tasks which is partly due to the lack of process specificity of the tasks applied. Therefore, we investigated WM functioning in patients with schizophrenia using process- and circuit-specific tasks. Thirty-one patients with schizophrenia and 47 controls were tested with respect to different aspects of verbal and visuospatial working memory using modified Sternberg paradigms in a computer-based behavioural experiment. Total group analysis revealed significant impairment of patients with schizophrenia in each of the tested WM components. Furthermore, we were able to identify subgroups of patients showing different patterns of selective deficits. Patients with schizophrenia exhibit specific and, in part, selective WM deficits with indirect but conclusive evidence of dysfunctions of the underlying neural networks. These deficits are present in tasks requiring only maintenance of verbal or visuospatial information. In contrast to a seemingly global working memory deficit, individual analysis revealed differential patterns of working memory impairments in patients with schizophrenia.

Prefrontal cortical circuits in schizophrenia

Impaired cognitive functioning, including deficits in working memory, is considered to be a core and disabling feature of schizophrenia that is difficult to treat. Deficits in working memory in schizophrenia are attributable, at least in part, to specific pathological alterations in the neuronal circuitry of the dorsolateral prefrontal cortex that involve, but are not restricted to, disturbances in glutamate, GABA, and dopamine neurotransmission. Cannabis use provides an example of an environmental exposure that may have a deleterious impact on these neurotransmitter systems and thereby contribute to worsening of cognitive functioning in schizophrenia. Increasing knowledge of the nature of the molecular alterations in these cortical circuits may lead to the development of new pathophysiologically informed treatment options for cognitive deficits in schizophrenia.

Investigation of clinical factors influencing cognitive function in Japanese schizophrenia

Several investigators have reported cognitive dysfunction in chronic schizophrenia that was associated with insight and social skills. Such cognitive dysfunction seriously hinders an immediate return to normal life. Recently, Kaneda et al. reported that the Brief Assessment of Cognition in Schizophrenia, Japanese-language version (BACS-J) was superior in the evaluation of the cognitive function. We investigated which clinical factors (age, sex, duration of illness, level of education, smoking status, the Positive and Negative Syndrome Scale (PANSS) score and medication dosage) affected cognitive dysfunction in 115 Japanese schizophrenic patients, with the use of multiple regression analysis. We detected an association between composite score, verbal memory, working memory and executive function and PANSS total score. Moreover, most cognitive tasks were associated with a negative PANSS score but not a positive PANSS score or general score. We also showed an association between age and verbal fluency and attention in schizophrenia. In addition, anxiolytics/hypnotics (diazepam-equivalent) were associated with composite score, working memory and motor speed. In conclusion, cognitive function was associated with PANSS score, especially negative PANSS score. Because anxiolytics/hypnotics might have a detrimental influence on cognitive function, we strongly suggest that the use of anxiolytics/hypnotics be reduced in schizophrenics as much as possible.

Metacognition in schizophrenia: processes underlying patients' reflections on their own episodic memory

BACKGROUND

The aim of the study was to explore the processes underlying schizophrenia patients' reflections on their own memory. Cognitive deficits and insight problems are considered core symptoms of schizophrenia. Even when people fail to recall a solicited target, they can provide feeling of knowing (FOK) judgments that reflect their ability to judge the accessibility of the target in memory. The metamemory approach allows for direct and experimental quantification of the correspondence between the subjective judgments and the objective measures of memory performance. According to the accessibility hypothesis, FOK evaluations rely on the accessibility of partial and/or contextual information relevant to the memory target.

METHODS

The accessibility of partial information relating to a memory target was investigated in 21 patients and 21 healthy comparison subjects matched for age, gender, and level of education. The material to be learned consisted of four-letter nonsense tetragrams, with each letter providing partial information about the four-letter target.

RESULTS

The results show that despite memory recall (p < .01) and recognition impairments (p = .02) and lower FOK ratings (p < .05), patients' metamemory judgments increased linearly with the amount of partial information recalled (from one letter to four letters, p < .01). The products of memory retrieval were predictive of both their FOK judgments and their subsequent memory performance.

CONCLUSIONS

Schizophrenia patients are as capable as comparison subjects of relying on the products of memory retrieval to monitor accurately their awareness of what they do or do not know. The finding may be of interest for cognitive remediation.

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

Patients with schizophrenia exhibit substantial deficits in both working memory (WM) and long-term memory (LTM) tasks. While these two forms of memory are generally viewed as distinct, recent evidence from healthy subjects has challenged the robustness of the double-dissociation between these two types of memory. In light of an emerging view of WM and LTM as being subserved by a largely overlapping network of brain regions, it is possible that WM and LTM deficits in patients with schizophrenia share a common neurobiological substrate. This review revisits the functional neuroimaging literature on both WM and LTM in patients with schizophrenia with these considerations in mind, and reveals a number of commonalities in research findings in both literatures. While there is a paucity of direct evidence bearing on whether patient deficits in these tasks arise from a common functional abnormality, the available literature is consistent with the hypothesis that these deficits have the same origin.

Efficiency of working memory encoding in twins discordant for schizophrenia

It has been proposed that patients with schizophrenia and some of their relatives suffer from reduced neurocognitive efficiency, increasing their sensitivity to experimental task demands. The present study evaluated such a possibility during performance of a working memory task by schizophrenia patients and their co-twins along with a healthy control sample. Electrophysiological data were obtained from sets of nine twin pairs (monozygotic and dizygotic pairs collapsed) discordant for a diagnosis of schizophrenia and from nine matched healthy control twin pairs, during administration of a variable-load spatial working memory task. Event-related potentials (ERPs) were measured immediately after memory set onset and during a delay period. For correctly performed trials, slow-wave ERP activity measured during the late stimulus encoding and delay periods exhibited a significant Diagnostic Group-by-Memory Load interaction, with schizophrenia patients showing a differentially strong load effect. Patients' co-twins displayed an intermediate level of load sensitivity while healthy controls showed no significant load effect. These results support an inefficiency model of neurocognitive dysfunction in schizophrenia, a pattern that appears to be related to the pathogenesis and inheritance of the disorder. Furthermore, this inefficiency appeared during the late stimulus encoding stage of working memory functioning, possibly reflecting disruptions in stimulus representation consolidation.

Convergent approaches for defining functional imaging endophenotypes in schizophrenia

In complex genetic disorders such as schizophrenia, endophenotypes have potential utility both in identifying risk genes and in illuminating pathophysiology. This is due to their presumed status as closer in the etiopathological pathway to the causative genes than is the currently defining clinical phenomenology of the illness and thus their simpler genetic architecture than that of the full syndrome. There, many genes conferring slight individual risk are additive or epistatic (interactive) with regard to cumulative schizophrenia risk. In addition the use of endophenotypes has encouraged a conceptual shift away from the exclusive study of categorical diagnoses in manifestly ill patients, towards the study of quantitative traits in patients, unaffected relatives and healthy controls. A more recently employed strategy is thus to study unaffected first-degree relatives of schizophrenia patients, who share some of the genetic diathesis without illness-related confounds that may themselves impact fMRI task performance. Consistent with the multiple biological abnormalities associated with the disorder, many candidate endophenotypes have been advanced for schizophrenia, including measures derived from structural brain imaging, EEG, sensorimotor integration, eye movements and cognitive performance (Allen et al., 2009), but recent data derived from quantitative functional brain imaging measures present additional attractive putative endophenotypes. We will review two major, conceptually different approaches that use fMRI in this context. One, the dominant paradigm, employs defined cognitive tasks on which schizophrenia patients perform poorly as "cognitive stress tests". The second uses very simple probes or "task-free" approaches where performance in patients and controls is equal. We explore the potential advantages and disadvantages of each method, the associated data analytic approaches and recent studies exploring their interface with the genetic risk architecture of schizophrenia.

The acute effects of synthetic intravenous Delta9-tetrahydrocannabinol on psychosis, mood and cognitive functioning

BACKGROUND

Recent work suggests that heavy use of cannabis is associated with an increased risk of schizophrenia-like psychosis. However, there is a dearth of experimental studies of the effects of the constituents of cannabis, such as Delta9-tetrahydrocannabinol (THC). In a study of intravenous (i.v.) synthetic THC in healthy humans, we aimed to study the relationship of the psychotic symptoms induced by THC to the consequent anxiety and neuropsychological impairment.

METHOD

Twenty-two healthy adult males aged 28+/-6 years (mean+/-s.d.) participated in experimental sessions in which i.v. THC (2.5 mg) was administered under double-blind, placebo-controlled conditions. Self-rated and investigator-rated measurements of mood and psychosis [the University of Wales Institute of Science and Technology Mood Adjective Checklist (UMACL), the Positive and Negative Syndrome Scale (PANSS) and the Community Assessment of Psychic Experiences (CAPE)] were made at baseline and at 30, 80 and 120 min post-injection. Participants also completed a series of neuropsychological tests [the Rey Auditory Verbal Learning Task (RAVLT), Digit Span, Verbal Fluency and the Baddeley Reasoning Task] within 45 min of injection.

RESULTS

THC-induced positive psychotic symptoms, and participant- and investigator-rated measurements of these were highly correlated. Participants showed an increase in anxiety ratings but there was no relationship between either self- or investigator-rated positive psychotic symptoms and anxiety. THC also impaired neuropsychological performance but once again there was no relationship between THC-induced positive psychotic symptoms and deficits in working memory/executive function.

CONCLUSIONS

These findings confirm that THC can induce a transient, acute psychotic reaction in psychiatrically well individuals. The extent of the psychotic reaction was not related to the degree of anxiety or cognitive impairment.

When doors of perception close: bottom-up models of disrupted cognition in schizophrenia

Schizophrenia is a major mental disorder that affects approximately 1% of the population worldwide. Cognitive deficits are a key feature of schizophrenia and a primary cause of long-term disability. Current neurophysiological models of schizophrenia focus on distributed brain dysfunction with bottom-up as well as top-down components. Bottom-up deficits in cognitive processing are driven by impairments in basic perceptual processes that localize to primary sensory brain regions. Within the auditory system, deficits are apparent in elemental sensory processing, such as tone matching following brief delay. Such deficits lead to impairments in higher-order processes such as phonological processing and auditory emotion recognition. Within the visual system, deficits are apparent in functioning of the magnocellular visual pathway, leading to higher-order deficits in processes such as perceptual closure, object recognition, and reading. In both auditory and visual systems, patterns of deficit are consistent with underlying impairment of brain N-methyl-d-aspartate receptor systems.

Attentional set-shifting ability in first-episode and established schizophrenia: Relationship to working memory

Patients with established schizophrenia perform poorly on attentional set-shifting tasks, due to a failure of inhibitory control and/or perseverative errors. However, attentional set-shifting is also dependent on working memory capacity, which is additionally impaired in schizophrenia. No studies in first-episode psychosis have specifically examined the contribution of working memory to set-shifting ability in schizophrenia. We investigated 48 first-episode schizophreniform psychosis/schizophrenia (FE) and 40 chronic schizophrenia (CHR) patients, compared to 67 comparable healthy subjects (CTL). All subjects were assessed using the CANTAB 'attentional set-shifting (IDED)' and 'spatial working memory (SWM)' tasks. Both FE and CHR made significantly greater errors on the SWM task (p< or =0.001). Compared with CTL, CHR was more likely to fail at intra-dimensional (p<0.05) and extra-dimensional (p<0.01) shifting and reversal stages of IDED; CHR required significantly greater trials to reach criterion, which was not explained by deficits in SWM (p<0.001). FE did not differ from CTL on IDED level reached. However, FE required significantly more trials (p=0.001); this was no longer significant after controlling for SWM deficits (p>0.05). Given that the capacity to be flexible and shift attentional set is intact only at the early stages of illness, 'neurodegenerative' processes may explain the more severe deficits in chronic schizophrenia. In contrast, deficits in SWM identified at all stages of schizophrenia may reflect incomplete maturation prior to illness onset ('neurodevelopmental arrest'). Longitudinal studies assessing these cognitive functions from illness onset or in prepsychotic individuals are required.

Turning it upside down: areas of preserved cognitive function in schizophrenia

Patients with schizophrenia demonstrate marked impairments on most clinical neuropsychological tests. These findings suggest that patients suffer from a generalized form of cognitive impairment, with little evidence of spared performance documented in several large meta-analytic reviews of the clinical literature. In contrast, we review evidence for relative sparing of aspects of attention, procedural memory, and emotional processing observed in studies that have employed experimental approaches adapted from the cognitive and affective neuroscience literature. These islands of preserved performance suggest that the cognitive deficits in schizophrenia are not as general as they appear to be when assayed with clinical neuropsychological methods. The apparent contradiction in findings across methods may offer important clues about the nature of cognitive impairment in schizophrenia. The documentation of preserved cognitive function in schizophrenia may serve to sharpen hypotheses about the biological mechanisms that are implicated in the illness.

Genes, cognition and brain through a COMT lens

Various genes are known to modulate the delicate balance of dopamine in prefrontal cortex and influence cortical information processing. Catechol-O-methyltransferase (COMT) on chromosome 22q11 is the most widely studied of these genes. Val158Met, a common, functional variant in the coding sequence that increases or decreases the enzymatic activity of the gene has been shown to impact the efficiency of prefrontally-mediated cognition, specifically executive functioning, working memory, fluid intelligence and attentional control. We review the rapidly evolving literature exploring the association between COMT genotype and cognitive performance, and illustrate how this polymorphism has served a pivotal role in characterizing various interacting dimensions of complexity in the relationship between genes and cognition. We review how Val158Met has been used to help develop and validate behavioral and neurophysiological phenotypes, as a critical tool in dissecting overlapping neural functional systems and exploring interactions within and between genes, and in exploring how gene effects on cognition are modulated by environmental, demographic and developmental factors. Despite the impressive range of findings, the COMT story is also a bracing reminder of how much work remains to translate this knowledge into practical clinical applications.

Schizophrenia, "just the facts" 4. Clinical features and conceptualization

Although dementia praecox or schizophrenia has been considered a unique disease entity for the past century, its definitions and boundaries have continued to vary over this period. At any given time, the changing concept of schizophrenia has been influenced by available diagnostic tools and treatments, related conditions from which it most needs to be distinguished, extant knowledge and scientific paradigms. There is significant heterogeneity in the etiopathology, symptomatology, and course of schizophrenia. It is characterized by an admixture of positive, negative, cognitive, mood, and motor symptoms whose severity varies across patients and through the course of the illness. Positive symptoms usually first begin in adolescence or early adulthood, but are often preceded by varying degrees of negative and cognitive symptomatology. Schizophrenia tends to be a chronic and relapsing disorder with generally incomplete remissions, variable degrees of functional impairment and social disability, frequent comorbid substance abuse, and decreased longevity. Although schizophrenia may not represent a single disease with a unitary etiology or pathogenetic process, alternative approaches have thus far been unsuccessful in better defining this syndrome or its component entities. The symptomatologic, course, and etio-pathological heterogeneity can usefully be addressed by a dimensional approach to psychopathology, a clinical staging approach to illness course, and by elucidating endophenotypes and markers of illness progression, respectively. This will allow an approach to the deconstruction of schizophrenia into its multiple component parts and strategies to reconfigure these components in a more meaningful manner. Possible implications for DSM-V and ICD-11 definitions of schizophrenia are discussed.

Schizophrenia from a neural circuitry perspective: advancing toward rational pharmacological therapies

Schizophrenia is a severe disorder that disrupts the function of multiple brain systems, resulting in impaired social and occupational functioning. The etiology and pathogenesis of schizophrenia appear to involve the interplay of a potentially large number of genetic liabilities and adverse environmental events that disrupt brain developmental pathways. In this Review, we discuss a strategy for determining how particular common and core clinical features of the illness are associated with pathophysiology in certain circuits of the cerebral cortex. The identification of molecular alterations in these circuits is providing critical insights for the rational development of new therapeutic interventions.

Prenatal protein deprivation alters dopamine-mediated behaviors and dopaminergic and glutamatergic receptor binding

Epidemiological evidence indicates that prenatal nutritional deprivation may increase the risk of schizophrenia. The goal of these studies was to use an animal model to examine the effects of prenatal protein deprivation on behaviors and receptor binding with relevance to schizophrenia. We report that prenatally protein deprived (PD) female rats showed an increased stereotypic response to apomorphine and an increased locomotor response to amphetamine in adulthood. These differences were not observed during puberty. No changes in haloperidol-induced catalepsy or MK-801-induced locomotion were seen following PD. In addition, PD female rats showed increased (3)H-MK-801 binding in the striatum and hippocampus, but not in the cortex. PD female rats also showed increased (3)H-haloperidol binding and decreased dopamine transporter binding in striatum. No statistically significant changes in behavior or receptor binding were found in PD males with the exception of increased (3)H-MK-801 binding in cortex. This animal model may be useful to explore the mechanisms by which prenatal nutritional deficiency enhances risk for schizophrenia in humans and may also have implications for developmental processes leading to differential sensitivity to drugs of abuse.