Information processing deficits of schizophrenia patients: relationship to clinical ratings, gender and medication status

Both unmedicated and medicated individuals with schizophrenia show impairments across a wide array of cognitive and reinforcement learning tasks

BACKGROUND

Schizophrenia is a disorder characterized by pervasive deficits in cognitive functioning. However, few well-powered studies have examined the degree to which cognitive performance is impaired even among individuals with schizophrenia not currently on antipsychotic medications using a wide range of cognitive and reinforcement learning measures derived from cognitive neuroscience. Such research is particularly needed in the domain of reinforcement learning, given the central role of dopamine in reinforcement learning, and the potential impact of antipsychotic medications on dopamine function.

METHODS

The present study sought to fill this gap by examining healthy controls (N = 75), unmedicated (N = 48) and medicated (N = 148) individuals with schizophrenia. Participants were recruited across five sites as part of the CNTRaCS Consortium to complete tasks assessing processing speed, cognitive control, working memory, verbal learning, relational encoding and retrieval, visual integration and reinforcement learning.

RESULTS

Individuals with schizophrenia who were not taking antipsychotic medications, as well as those taking antipsychotic medications, showed pervasive deficits across cognitive domains including reinforcement learning, processing speed, cognitive control, working memory, verbal learning and relational encoding and retrieval. Further, we found that chlorpromazine equivalency rates were significantly related to processing speed and working memory, while there were no significant relationships between anticholinergic load and performance on other tasks.

CONCLUSIONS

These findings add to a body of literature suggesting that cognitive deficits are an enduring aspect of schizophrenia, present in those off antipsychotic medications as well as those taking antipsychotic medications.

Early visual processing and adaptation as markers of disease, not vulnerability: EEG evidence from 22q11.2 deletion syndrome, a population at high risk for schizophrenia

We investigated visual processing and adaptation in 22q11.2 deletion syndrome (22q11.2DS), a condition characterized by an increased risk for schizophrenia. Visual processing differences have been described in schizophrenia but remain understudied early in the disease course. Electrophysiology was recorded during a visual adaptation task with different interstimulus intervals to investigate visual processing and adaptation in 22q11.2DS (with (22q+) and without (22q−) psychotic symptoms), compared to control and idiopathic schizophrenia groups. Analyses focused on early windows of visual processing. While increased amplitudes were observed in 22q11.2DS in an earlier time window (90–140 ms), decreased responses were seen later (165–205 ms) in schizophrenia and 22q+. 22q11.2DS, and particularly 22q−, presented increased adaptation effects. We argue that while amplitude and adaptation in the earlier time window may reflect specific neurogenetic aspects associated with a deletion in chromosome 22, amplitude in the later window may be a marker of the presence of psychosis and/or of its chronicity/severity.

Gender Difference in Cognitive Function Among Stable Schizophrenia: A Network Perspective

OBJECTIVE

To investigate the gender differences and influencing factors of cognitive function in stable schizophrenic patients, and to explore the cognitive characteristics of male and female patients.

METHODS

A total of 298 patients with chronic schizophrenia were divided into two groups according to gender. The differences of demographic and clinical characteristics between the two groups were firstly analyzed. Then the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) was used to measure their cognitive function, and the correlation between cognitive function and demographic characteristics and clinical characteristics was analyzed. Finally, the gender-based cognitive characteristics were explored through network analysis.

RESULTS

There was no significant difference in the RBANS total score and sub-item score between the male schizophrenia and female schizophrenia patients. Correlation analysis showed that RBANS total score was inversely proportional with age, duration and Positive and Negative Syndrome Scale (PANSS) score in male schizophrenia, while being directly proportional with age at onset and inversely proportional with PANSS score in female schizophrenia. Network analysis showed that language was the core of cognitive function for male schizophrenia, and the delayed memory was the core of cognitive function for female schizophrenia.

CONCLUSION

There was no significant gender difference in cognitive function score among patients with stable schizophrenia. The core cognitive functions of male and female schizophrenia are language and delayed memory, respectively.

Atypically larger variability of resource allocation accounts for visual working memory deficits in schizophrenia

Working memory (WM) deficits have been widely documented in schizophrenia (SZ), and almost all existing studies attributed the deficits to decreased capacity as compared to healthy control (HC) subjects. Recent developments in WM research suggest that other components, such as precision, also mediate behavioral performance. It remains unclear how different WM components jointly contribute to deficits in schizophrenia. We measured the performance of 60 SZ (31 females) and 61 HC (29 females) in a classical delay-estimation visual working memory (VWM) task and evaluated several influential computational models proposed in basic science of VWM to disentangle the effect of various memory components. We show that the model assuming variable precision (VP) across items and trials is the best model to explain the performance of both groups. According to the VP model, SZ exhibited abnormally larger variability of allocating memory resources rather than resources or capacity per se. Finally, individual differences in the resource allocation variability predicted variation of symptom severity in SZ, highlighting its functional relevance to schizophrenic pathology. This finding was further verified using distinct visual features and subject cohorts. These results provide an alternative view instead of the widely accepted decreased-capacity theory and highlight the key role of elevated resource allocation variability in generating atypical VWM behavior in schizophrenia. Our findings also shed new light on the utility of Bayesian observer models to characterize mechanisms of mental deficits in clinical neuroscience.

Working memory is a core cognitive function related to a broad range of cognitive domains such as problem-solving, attention, executive control, and IQ. Although working memory deficits have been well-documented in schizophrenia, the underlying mechanisms remain unclear. Conventional working memory theories attribute working memory deficits in schizophrenia to their reduced memory capacity, overlooking the potential roles of other memory components, such as precision. In this study, we take the approach of computational psychiatry and use computational modeling to uncover the major determinants of working memory deficits. We assess working memory performance of a large cohort of participants (60 schizophrenia patients and 61 demographic matched healthy controls) and evaluate multiple mainstream computational models of visual working memory. The variable precision model turns out to be the best model for both groups. We further find that the poorer performance of schizophrenia patients arises from heterogeneous distribution of memory resources when encoding items in memory. This resource allocation variability can also predict symptom severity in schizophrenia. Our study highlights the use of computational models in psychiatric researches.

Functional brain imaging of speeded decision processing in Parkinson's disease and comparison with Schizophrenia

This study examined whether Parkinson's disease (PD¹) and schizophrenia (SCZ²) share a hypo dopaminergic dysfunction of the prefrontal cortex leading to cognitive impairments in decision processing. 24 medicated PD patients and 28 matched controls performed the Eriksen flanker two-choice reaction time (RT³) task while brain activity was measured throughout, using functional Magnetic Resonance Imaging (fMRI⁴). Results were directly compared to those of 30 SCZ patients and 30 matched controls. Significant differences between SCZ and PD were found, through directly comparing the z-score deviations from healthy controls across all behavioral measures, where only SCZ patients showed deviances from controls. Similarly a direct comparison of z-score activation deviations from controls indicated significant differences in prefrontal and cingulate cortical activation between SCZ and PD, where only SCZ patients showed hypo-activation of these areas compared to controls. The hypo-activation of the dorsolateral prefrontal cortex was related to larger RT variability (ex-Gaussian tau) in SCZ but not PD patients. Overall, the concluding evidence does not support a shared neural substrate of cognitive dysfunction, since the deficit in speeded decision processing and the related cortical hypo-activation observed in SCZ were absent in PD.

Hypo-activity of the dorsolateral prefrontal cortex relates to increased reaction time variability in patients with schizophrenia

Increased reaction time intra-subject variability (RT-ISV) in fast decision tasks has been confirmed in patients with schizophrenia and has been hypothesized to result from a deficit in the control of attention. Here, an attentional task and functional brain imaging were used to probe the neural correlates of increased RT-ISV in schizophrenia.

Thirty patients and 30 age and sex matched controls performed the Eriksen flanker spatial attention task with concurrent measurement of brain activity using functional magnetic resonance imaging (fMRI). The behavioral measures included accuracy, mean, standard deviation of RT (RTSD), coefficient of variation of RT (RTCV) and ex-Gaussian model of RT distribution parameters (mu, sigma and tau).

Larger mean RT and Ex-Gaussian mu was observed for patients compared to controls. The group difference was larger for incongruent (attentionally demanding) versus congruent trials confirming a deficit in the control of spatial attention for patients. Significant increase in RT-ISV measures (RTSD, sigma and tau) for patients compared to controls was observed and was not modulated by trial congruency. Attention modulation (congruency effect) resulted in activation of bilateral frontal and parietal areas that was not different between patients and controls. Right middle frontal, right superior temporal and bilateral cingulate areas were more active in controls compared to patients independent of congruency. Activation in ROIs extracted from attention (congruency) and group related areas correlated with RT-ISV measures (especially RTCV and tau). Hypo-activation of the right middle frontal area correlated with increased tau specifically in patients.

Hypo-activity of the right prefrontal cortex predicted increased RT-ISV in schizophrenia. This effect was unrelated to the effects of spatial attention and might be linked to a deficit in the inhibitory control of action for these patients.

•

Schizophrenia patients show increased reaction time intra-subject variability (RT-ISV).

•

fMRI of patients and aged matched controls while performing a spatial attention task.

•

RT-ISV measures were increased in patients independent of spatial attention load.

•

Activity of the right middle frontal cortex predicted RT-ISV increase in patients.

Schizophrenia patients using atypical medication perform better in visual tasks than patients using typical medication

Schizophrenia (SCZ) patients show deficits in many domains, including cognition and perception. However, results are often mixed. One reason for mixed results may be differences in medication. Very little is known about the role of medication in visual processing. Here, we investigated the effects of typical vs. atypical medication on contrast sensitivity (spatial frequencies ranging from 0.2 to 20 cycles per degree), vernier acuity, and visual backward masking. From a large pool of patients, we selected 50 patients (Study 1, conducted in Brazil) and 97 patients (Study 2, conducted in Georgia) taking either only typical or atypical medication. Patients with atypical medication performed significantly better than patients with typical medication for contrast sensitivity, vernier duration, and backward masking. As a secondary result, we found similar, but not significant, trends for the cognitive tasks (Stroop, Flanker, Trail-Making Test-B, Wisconsin Card Sorting Test and Continuous Performance Test) in the same patients. No correlations were found between demographics, psychopathology, chlorpromazine equivalents and visual processing. A conclusion of our study is that one needs to be careful comparing studies when medication is not comparable.

Modelling reaction time distribution of fast decision tasks in schizophrenia: Evidence for novel candidate endophenotypes

Increased reaction time (RT) and variability of RT in fast decision tasks is observed in patients with schizophrenia and their first degree relatives. This study used modelling of the RT distribution with the aim of identifying novel candidate endophenotypes for schizophrenia. 20 patients with schizophrenia, 15 siblings of patients and 25 healthy controls performed an oddball task of varying working memory load. Increases in mean and standard deviation (SD) of RT were observed for both patients and siblings compared to controls and they were again independent of working memory load. Ex-Gaussian modelling of the RT distribution confirmed that parameters μ, σ and τ increased significantly in patients and siblings compared to controls. The Drift Diffusion Model was applied on RT distributions. A decrease in the diffusion drift rate (v) modeling the accumulation of evidence for reaching the decision to choose one stimulus over the other, was observed in patients and siblings compared to controls. The mean time of the non-decisional sensorimotor processes (t0) and it's variance (st0) was also increased in patients and siblings compared to controls. In conclusion modeling of the RT distribution revealed novel potential cognitive endophenotypes in the quest of heritable risk factors for schizophrenia.

Probing the magnocellular and parvocellular visual pathways in facial emotion perception in schizophrenia

Schizophrenia patients have well-established deficits in facial emotion perception, which contribute to their poor social functioning. A number of studies have related these deficits to a differential dysfunction in the magnocellular (M) versus parvocellular (P) visual pathway. We assessed 35 schizophrenia patients and 35 healthy individuals on an emotion identification task, in which facial stimuli were either unaltered (broad spatial frequency, BSF) or manipulated to contain only high (HSF) or low (LSF) spatial frequencies, thereby respectively biasing the visual system toward the P- or M- pathways. As expected, patients were less accurate and slower in recognizing emotions across all conditions, relative to controls. Performance was best in the BSF condition followed by the HSF and finally the LSF condition, in both groups. A significant group by spatial frequency interaction reflected a smaller magnitude of impairment in the HSF condition, compared to the other two conditions that preferentially engage the M-system. These findings are consistent with studies showing a differential M-pathway abnormality in schizophrenia with a less pronounced impairment in P-function. The current study suggests that patients have less difficulty extracting emotional content from faces when LSFs are attenuated and supports the need to remediate basic visual processing deficits in schizophrenia.

Visual masking & schizophrenia

Visual masking is a frequently used tool in schizophrenia research. Visual masking has a very high sensitivity and specificity and masking paradigms have been proven to be endophenotypes. Whereas masking is a powerful technique to study schizophrenia, the underlying mechanisms are discussed controversially. For example, for more than 25 years, masking deficits of schizophrenia patients were mainly attributed to a deficient magno-cellular system (M-system). Here, we show that there is very little evidence that masking deficits are magno-cellular deficits. We will discuss the magno-cellular and other approaches in detail and highlight their pros and cons.

Effects of dopamine D2/D3 blockade on human sensory and sensorimotor gating in initially antipsychotic-naive, first-episode schizophrenia patients

It has been suggested that psychophysiological measures of sensory and sensorimotor gating, P50 gating and prepulse inhibition of the startle reflex (PPI), underlie core features of schizophrenia and are linked to dopaminergic pathways in the striatum and prefrontal cortex. In the present study, the effects of a potent D2/D3 receptor antagonist, amisulpride, were investigated on PPI and P50 gating in a large sample of antipsychotic-naive, first-episode patients with schizophrenia. A total of 52 initially antipsychotic-naive, first-episode schizophrenia patients were assessed for their P50 gating, PPI, and habituation/sensitization abilities at baseline and after 2 and 6 weeks of treatment with flexible doses of amisulpride. In addition, 47 matched healthy controls were assessed at baseline and after 6 weeks. At baseline, the patients showed significantly reduced PPI, yet normal levels of P50 gating, habituation, and sensitization. Treatment with amisulpride showed no effects on these measures, either at 2 or 6 weeks of follow-up. This is the first study investigating the effects of monotherapy with a relatively selective dopamine D2/D3 receptor antagonist (amisulpride) on sensory and sensorimotor gating deficits in a longitudinal study of a large group of initially antipsychotic-naive, first-episode patients with schizophrenia. Our finding that amisulpride effectively reduced symptom severity in our patients without reducing their PPI deficits indicates that increased activity of dopamine D2 receptors may be involved in symptomatology of patients with schizophrenia, but not in their sensorimotor gating deficits.

Self-attribution bias during continuous action-effect monitoring in patients with schizophrenia

The feeling of being the source and controller of one's actions and their effects in the outside world is an important aspect of our sense of self. Disturbances in this sense of agency (SoA) were observed in schizophrenia and have been linked to impairments in sensorimotor integration. We used a virtual-world action-monitoring paradigm to investigate the SoA in 20 schizophrenic patients and 18 healthy subjects. Participants continuously moved a virtual pen displayed on a computer screen using a touchpad device. The control they exceeded over the virtual pen was switched periodically between the participant and the computer. Participants were requested to monitor their actions and the effects on the virtual pen, and indicate loss or regain of control over the pen's movement by button presses. The numbers of erroneous external attribution of action effects (false negative agency judgements) and erroneous self-attribution (false positive agency judgements) were not significantly different in patients and healthy subjects. However, patients showed a significant increase in the duration of false negative agency judgements. Moreover, the number of false negative agency judgements as well as the number and the duration of false positive agency judgements were negatively correlated with the performance in cognitive tests (BACS) in the patient group only. Our findings indicate that the evaluation system to detect a mismatch between actions and their effects in the outside world is probably more rigid in schizophrenic patients, which leads to an increased self-attribution bias for action effects, as commonly found in delusions of control. The impairment in sensorimotor integration may be compensated for by stronger cognitive control.

Association of the Nicotinic Receptor α7 Subunit Gene (CHRNA7) with Schizophrenia and Visual Backward Masking

The nicotinic system is involved in the pathophysiology of schizophrenia. However, very little is known about its genetic basis and how it relates to clinical symptoms and potentially pharmacological intervention. Here, we investigated five single nucleotide polymorphisms (SNPs) [rs3826029] [rs2337506] [rs982574] [rs904952] [rs2337980] of the cholinergic nicotinic receptor gene, alpha 7 subunit (CHRNA7) and their association to schizophrenia. We found an association with rs904952 (p = 0.009) in a German sample of 224 schizophrenic patients and 224 healthy control subjects. The same trend was shown in an independent Georgian sample of 50 schizophrenic patients, 57 first order unaffected relatives, and 51 healthy controls. In addition, visual backward masking (VBM), a sensitive test for early visual information processing, was assessed in the Georgian sample. In line with prior studies, VBM performance deficits were much more pronounced in schizophrenic patients and their unaffected relatives compared to healthy controls (schizophrenic patients: 156 ms; unaffected relatives: 60 ms; healthy controls: 33 ms). VBM was strongly correlated with SNP rs904952 (H[2] = 7.3, p = 0.026). Our results further support the notion that changes in the nicotinic system are involved in schizophrenia and open the avenue for pharmacological intervention.

Schizophrenia and visual backward masking: a general deficit of target enhancement

The obvious symptoms of schizophrenia are of cognitive and psychopathological nature. However, schizophrenia affects also visual processing which becomes particularly evident when stimuli are presented for short durations and are followed by a masking stimulus. Visual deficits are of great interest because they might be related to the genetic variations underlying the disease (endophenotype concept). Visual masking deficits are usually attributed to specific dysfunctions of the visual system such as a hypo- or hyper-active magnocellular system. Here, we propose that visual deficits are a manifestation of a general deficit related to the enhancement of weak neural signals as occurring in all other sorts of information processing. We summarize previous findings with the shine-through masking paradigm where a shortly presented vernier target is followed by a masking grating. The mask deteriorates visual processing of schizophrenic patients by almost an order of magnitude compared to healthy controls. We propose that these deficits are caused by dysfunctions of attention and the cholinergic system leading to weak neural activity corresponding to the vernier. High density electrophysiological recordings (EEG) show that indeed neural activity is strongly reduced in schizophrenic patients which we attribute to the lack of vernier enhancement. When only the masking grating is presented, EEG responses are roughly comparable between patients and control. Our hypothesis is supported by findings relating visual masking to genetic deviants of the nicotinic α7 receptor (CHRNA7).

No evidence for prolonged visible persistence in patients with schizophrenia

BACKGROUND

Temporal visual processing is strongly deteriorated in patients with schizophrenia. For example, the interval required between a visual stimulus and a subsequent mask has to be much longer in schizophrenic patients than in healthy controls. We investigated whether this deficit in temporal resolution is accompanied by prolonged visual persistence and/or deficient temporal precision (temporal asynchrony perception).

METHODOLOGY/PRINCIPAL FINDINGS

We investigated visual persistence in three experiments. In the first, measuring temporal processing by so-called backward masking, prolonged visible persistence is supposed to decrease performance. In the second experiment, requiring temporal integration, prolonged persistence is supposed to improve performance. In the third experiment, we investigated asynchrony detection, as another measure of temporal resolution. Eighteen patients with schizophrenia and 15 healthy controls participated. Asynchrony detection was intact in the patients. However, patients' performance was inferior compared to healthy controls in the first two experiments. Hence, temporal processing in schizophrenic patients is indeed significantly impaired but this impairment is not caused by prolonged temporal integration.

CONCLUSIONS/SIGNIFICANCE

Our results argue against a generally prolonged visual persistence in patients with schizophrenia. Together with the preserved ability of patients, to detect temporal asynchronies in permanently presented stimuli, the results indicate a more specific deficit in temporal processing of schizophrenic patients.

Object substitution masking in schizophrenia: an event-related potential analysis

Schizophrenia patients exhibit deficits on visual processing tasks, including visual backward masking, and these impairments are related to deficits in higher-level processes. In the current study we used electroencephalography techniques to examine successive stages and pathways of visual processing in a specialized masking paradigm, four-dot masking, which involves masking by object substitution. Seventy-six schizophrenia patients and 66 healthy controls had event-related potentials (ERPs) recorded during four-dot masking. Target visibility was manipulated by changing stimulus onset asynchrony (SOA) between the target and mask, such that performance decreased with increasing SOA. Three SOAs were used: 0, 50, and 100 ms. The P100 and N100 perceptual ERPs were examined. Additionally, the visual awareness negativity (VAN) to correct vs. incorrect responses, an index of reentrant processing, was examined for SOAs 50 and 100 ms. Results showed that patients performed worse than controls on the behavioral task across all SOAs. The ERP results revealed that patients had significantly smaller P100 and N100 amplitudes, though there was no effect of SOA on either component in either group. In healthy controls, but not patients, N100 amplitude correlated significantly with behavioral performance at SOAs where masking occurred, such that higher accuracy correlated with a larger N100. Healthy controls, but not patients, exhibited a larger VAN to correct vs. incorrect responses. The results indicate that the N100 appears to be related to attentional effort in the task in controls, but not patients. Considering that the VAN is thought to reflect reentrant processing, one interpretation of the findings is that patients' lack of VAN response and poorer performance may be related to dysfunctional reentrant processing.

Brief monocular deprivation as an assay of short-term visual sensory plasticity in schizophrenia - "the binocular effect"

BACKGROUND

Visual sensory processing deficits are consistently observed in schizophrenia, with clear amplitude reduction of the visual evoked potential (VEP) during the initial 50-150 ms of processing. Similar deficits are seen in unaffected first-degree relatives and drug-naïve first-episode patients, pointing to these deficits as potential endophenotypic markers. Schizophrenia is also associated with deficits in neural plasticity, implicating dysfunction of both glutamatergic and GABAergic systems. Here, we sought to understand the intersection of these two domains, asking whether short-term plasticity during early visual processing is specifically affected in schizophrenia.

METHODS

Brief periods of monocular deprivation (MD) induce relatively rapid changes in the amplitude of the early VEP - i.e., short-term plasticity. Twenty patients and 20 non-psychiatric controls participated. VEPs were recorded during binocular viewing, and were compared to the sum of VEP responses during brief monocular viewing periods (i.e., Left-eye + Right-eye viewing).

RESULTS

Under monocular conditions, neurotypical controls exhibited an effect that patients failed to demonstrate. That is, the amplitude of the summed monocular VEPs was robustly greater than the amplitude elicited binocularly during the initial sensory processing period. In patients, this "binocular effect" was absent.

LIMITATIONS

Patients were all medicated. Ideally, this study would also include first-episode unmedicated patients.

CONCLUSION

These results suggest that short-term compensatory mechanisms that allow healthy individuals to generate robust VEPs in the context of MD are not effectively activated in patients with schizophrenia. This simple assay may provide a useful biomarker of short-term plasticity in the psychotic disorders and a target endophenotype for therapeutic interventions.

Visual information processing dysfunction across the developmental course of early psychosis

BACKGROUND

Patients with schizophrenia consistently demonstrate information processing abnormalities assessed with visual masking (VM) tasks, and these deficits have been linked to clinical and functional severity. It has been suggested that VM impairments may be a vulnerability marker in individuals at risk for developing psychosis.

METHOD

Forward and backward VM performance was assessed in 72 first-episode (FE) psychosis patients, 98 subjects at risk (AR) for psychosis and 98 healthy controls (HC) using two identification tasks (with either a high- or low-energy mask) and a location task. VM was examined for stability in a subgroup (FE, n=15; AR, n=35; HC, n=21) and assessed relative to clinical and functional measures.

RESULTS

In the identification tasks, backward VM deficits were observed in both FE and AR relative to HC whereas forward VM deficits were only present in FE patients compared to HC. In the location task, AR subjects demonstrated superior performance in forward VM relative to HC. VM performance was stable over time, and VM deficits were associated with baseline functional measures and predicted future negative symptom severity in AR subjects.

CONCLUSIONS

Visual information processing deficits, as indexed by backward VM, are present before and after the onset of frank psychosis, and probably represent a stable vulnerability marker that is associated with negative symptoms and functional decline. Additionally, the paradoxically better performance of AR subjects in select forward tasks suggests that early compensatory changes may characterize an emerging psychotic state.

Neuroanatomical circuitry associated with exploratory eye movement in schizophrenia: a voxel-based morphometric study

Schizophrenic patients present abnormalities in a variety of eye movement tasks. Exploratory eye movement (EEM) dysfunction appears to be particularly specific to schizophrenia. However, the underlying mechanisms of EEM dysfunction in schizophrenia are not clearly understood. To assess the potential neuroanatomical substrates of EEM, we recorded EEM performance and conducted a voxel-based morphometric analysis of gray matter in 33 schizophrenic patients and 29 well matched healthy controls. In schizophrenic patients, decreased responsive search score (RSS) and widespread gray matter density (GMD) reductions were observed. Moreover, the RSS was positively correlated with GMD in distributed brain regions in schizophrenic patients. Furthermore, in schizophrenic patients, some brain regions with neuroanatomical deficits overlapped with some ones associated with RSS. These brain regions constituted an occipito-tempro-frontal circuitry involved in visual information processing and eye movement control, including the left calcarine cortex [Brodmann area (BA) 17], the left cuneus (BA 18), the left superior occipital cortex (BA 18/19), the left superior frontal gyrus (BA 6), the left cerebellum, the right lingual cortex (BA 17/18), the right middle occipital cortex (BA19), the right inferior temporal cortex (BA 37), the right dorsolateral prefrontal cortex (BA 46) and bilateral precentral gyri (BA 6) extending to the frontal eye fields (FEF, BA 8). To our knowledge, we firstly reported empirical evidence that gray matter loss in the occipito-tempro-frontal neuroanatomical circuitry of visual processing system was associated with EEM performance in schizophrenia, which may be helpful for the future effort to reveal the underlying neural mechanisms for EEM disturbances in schizophrenia.

Factor structure of the BPRS in deaf people with schizophrenia: correlates to language and thought

INTRODUCTION

There has been a relative lack of research on deaf people with schizophrenia, and no data exist regarding symptom structure in this population. Thus, we determined the factor structure of the 24-item Brief Psychiatric Rating Scale (BPRS) in deaf (n = 34) and hearing (n = 31) people with schizophrenia and compared it to a standard four-factor solution.

METHOD

An obliquely rotated factor analysis produced a solution for the BPRS that resembled others in the literature. Symptom clusters were additionally compared to cognitive and social-cognitive abilities.

RESULTS

Activity and disorganised symptoms were the most consistent correlates of visual- and thought and language-related skills for deaf and hearing subjects respectively. Affective symptoms and facial affect processing were positively correlated among deaf but not hearing subjects.

CONCLUSIONS

The data suggest that current symptom models of schizophrenia are valid in both hearing and deaf patients. However, relations between symptoms, cognition, and outcome from the general (hearing) literature cannot be generalised to deaf patients. Findings are broadly consistent with pathophysiologic models of schizophrenia suggesting a fundamental cortical processing algorithm operating across several domains of neural activity including vision, and thought and language. Support is provided for recent advances in social-cognitive interventions for people with schizophrenia.

Are masking abnormalities in schizophrenia specific to type-B masking?

The abnormal visual masking in those with schizophrenia, it has been proposed, arises from a deficiency in their magnocellular system. Two kinds of masking exist: Type-A and Type-B. Type-A masking is characterized by the masking being strongest when target and mask are presented simultaneously. Type-B masking is characterized by a non-monotonic masking curve, i.e. the masking is largest when the mask is presented at some time after the target. The proposed link between masking and magnocellular activity applies mainly to Type-B masking. Thus, a magnocellular deficiency, if it exists, should effect Type-B masking more prominently than Type-A masking. Here we review the relevant literature. The majority of studies of masking in those with schizophrenia, it is found, have examined only Type-A masking. These find substantial evidence for abnormal masking. Where Type-B masking has been obtained, evidence also exists for abnormalities. However, the abnormal masking in these cases is largely unrelated to the defining characteristic of Type-B masking (i.e. to the non-monotonic masking function). It is concluded that the evidence for linking masking abnormalities in schizophrenia specifically to Type-B masking is weak. This undermines the proposal that masking abnormalities in schizophrenia have a magnocellular origin.

Stereopsis and magnocellular sensitivity in schizophrenia

There is evidence to indicate that schizophrenic individuals, in addition to cognitive deficiencies, also suffer from visual deficits. These deficits, it has been proposed, are the result of a deficiency in the magnocellular portion of the early visual system. A number of approaches have been used in attempts to assess the sensitivity of the magnocellular system in individuals with schizophrenia. It has recently been proposed that magnocellular sensitivity can be tested by measuring stereo acuity, i.e. by measuring the accuracy with which visual depth can be detected based on differences in the retinal images in the two eyes. This suggestion was based on early claims which linked stereopsis, i.e. the visual perception of depth generated from differences in the two retinal images, to the magnocellular system. We here review more recent results which indicate that stereopsis and stereo acuity are more closely linked to the parvocellular system. It is concluded that stereo acuity is not an appropriate test for assessing magnocellular sensitivity. The present considerations undermine the claim that magnocellular deficits are linked to schizophrenia.

The relationship between IQ, memory, executive function, and processing speed in recent-onset psychosis: 1-year stability and clinical outcome

Studies commonly report poor performance in psychotic patients compared with controls on tasks testing a range of cognitive functions, but, because current IQ is often not matched between these groups, it is difficult to determine whether this represents a generalized deficit or specific abnormalities. Fifty-three first-episode psychosis patients and 53 healthy controls, one-to-one matched for sex, age, and full-scale current IQ, were compared on Wechsler Adult Intelligence Scale (WAIS) subtests representing indices of perceptual organization, verbal comprehension, processing speed, and working memory as well as other tests of executive function and episodic memory. The groups showed an equivalent pattern of performance on all WAIS subtests except digit symbol processing speed, on which the patients were significantly worse. Patients were also worse on measures where performance correlated with digit symbol score, namely working and verbal memory tasks. Standardized residual scores for each subtest were calculated for each patient using the difference between their actual subtest score and a predicted subtest score based on their full-scale IQ and the performance of controls. Scaled scores and residual scores were examined for relationships with clinical measures. Digit symbol-scaled score was significantly correlated with concurrent negative syndrome score at baseline, and digit symbol residual score significantly predicted residual negative symptoms at 1-year follow-up. In summary, our comparison of patients and controls precisely matched for IQ revealed that processing speed was attenuated in recent-onset schizophrenia, contributed significantly to working and episodic memory deficits, and was a prognostic factor for poor outcome at 1 year.

Fluctuation of gamma-band phase synchronization within the auditory cortex in schizophrenia

OBJECTIVE

To study the phase stability of the 40Hz auditory steady-state response (ASSR) in Sz, and in addition, to investigate inter-hemispheric phase synchronization using ipsilateral and contralateral hemisphere gamma band ASSRs.

METHODS

Whole head magnetoencephalography (MEG) was used to detect ASSR from both hemispheres in Sz patients and their control counterparts. Source localization, spatial and temporal filtering were performed to infer gamma band activity from the neural generators of the ASSR. The response gamma band phase stability relative to a reference signal was quantified using the phase synchronization index (PSI).

RESULTS

Results indicated reduced phase synchronization of the ASSR and the stimulus reference signal in Sz patients compared to control subjects, in addition to reduced inter-hemispheric phase synchronization between contralateral and ipsilateral hemispheric responses in Sz patients.

CONCLUSIONS

Greater intra and inter hemispheric fluctuations of ASSR gamma band phase synchronization in Sz add to previous studies suggesting timing deficiencies within neural populations, possibly caused by impairments of neural network parameters.

SIGNIFICANCE

This study provides experimental support that may aid in understanding the dynamics of neural phase synchrony caused by modifications of underlying neurotransmitter systems, as reflected in disease states such as schizophrenia.

Are masking abnormalities in schizophrenia limited to backward masking?

Schizophrenia, it has been proposed, is associated with deficits in the magnocellular part of the visual system. In support of this suggestion, it has been claimed that schizophrenic subjects have abnormal backward masking. However, if this abnormality is to be linked specifically to magnocellular defects, then it must be specific to backward masking, and not, also effect, for example, forward masking. We examined this issue by reviewing the studies of masking in schizophrenic subjects. We find: (i) Most studies (56 out of 67) of backward masking have researched only backward masking. This makes it impossible to determine if the abnormalities found in these studies are exclusively confined to backward masking. (ii) Of those studies (11) that have included both forward and backward masking conditions, the majority found some degree of abnormality under both forward and backward masking conditions. It is concluded that the evidence for linking the abnormalities found in those with schizophrenia specifically to backward masking, rather than masking in general, or more general visual impairments, is at present relatively weak. Given the rationale for using backward masking as a test of magnocellular sensitivity, research in this area does not point to a deficit specific to the magnocellular system.

Is executive impairment associated with schizophrenic syndromes? A meta-analysis

BACKGROUND

A key neuropsychological proposal in schizophrenia is that negative and disorganization symptoms are associated with different patterns of impairment on executive tasks.

METHOD

Studies reporting correlations between positive, negative or disorganization symptoms and any type of executive test were meta-analysed. The influence of moderating factors was also examined, including age, treatment and stage of illness and whether symptoms were relapsing or persistent. The magnitudes of the correlations were compared with those for general intellectual impairment.

RESULTS

Pooled correlations between executive impairment and both negative symptoms and disorganization were significant in the small-to-moderate range. That for positive symptoms ('reality distortion'), however, was close to zero. The pattern of correlations among different executive tests differed significantly for negative symptoms and disorganization. Patients with stable clinical pictures showed significantly higher correlations with executive impairment than those with relapsing and remitting illnesses. Both negative symptoms and disorganization also correlated significantly with general intellectual function as indexed by current IQ.

CONCLUSIONS

Meta-analysis supports the view that negative symptoms and disorganization are associated with partially dissociable patterns of executive impairment. However, co-existent general intellectual impairment has been an important confounding factor in the studies to date.

Do sex differences affect prefrontal cortex associated cognition in schizophrenia?

Cognitive deficits in schizophrenia, especially those related to prefrontal cortex (PFC) functions, influence functional outcome. There is evidence for sex differences in cognition in schizophrenia, but the results in the literature are still controversial.

OBJECTIVE

This study evaluated different modalities of working memory (WM) and executive control (EC), functions that are both associated with the PFC, between sexes in schizophrenic patients and controls.

METHODS

We used a battery of neuropsychological tests for assessing auditory, spatial, and visual-matching WM and used a dual task for assessing EC. The study included 50 inpatients (25 female) partially remitted and taking atypical neuroleptics, as well as 40 controls (20 female) matched for age and education.

RESULTS

Significant sex differences were found in the dual task; female patients detected fewer correct trials than male patients and controls did. Moreover, female patients performed significantly worse in the single visual subtest of the dual task. For the controls, no sex differences were found. Males showed higher positive symptoms than females, but no other differences in psychopathology, disease characteristics, or extrapyramidal symptoms were found between sexes.

CONCLUSION

The present study shows an absence of sex differences in WM in healthy subjects and in patients with schizophrenia. However, in the dual task and in the single visual subtest, female patients performed worse than males. This finding suggests that in contrast to males, nonacute female inpatients show an underlying attentional deficit that may contribute to impairment in higher-order functions such as EC.

D-aspartate prevents corticostriatal long-term depression and attenuates schizophrenia-like symptoms induced by amphetamine and MK-801

Since their discovery in the mammalian CNS, D-aspartate and D-serine have aroused a strong interest with regard to their role as putative neuromodulatory molecules. Whereas the functional role of D-serine as an endogenous coagonist of NMDA receptors (NMDARs) has been elucidated, the biological significance of D-aspartate in the brain is still mostly unclear. In the present study, we demonstrated that nonphysiological high levels of D-aspartate (1) increased in vivo NMDAR activity, (2) attenuated prepulse inhibition deficits induced by amphetamine and MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine hydrogen maleate], (3) produced striatal adaptations of glutamate synapses resembling those observed after chronic haloperidol treatment, and (4) enhanced hippocampal NMDAR-dependent memory. This evidence was obtained using two different experimental strategies that produced an abnormal increase of endogenous D-aspartate levels in the mouse: a genetic approach based on the targeted deletion of the D-aspartate oxidase gene and a pharmacological approach based on oral administration of D-aspartate. This work provides in vivo evidence of a neuromodulatory role exerted by D-aspartate on NMDAR signaling and raises the intriguing hypothesis that also this D-amino acid, like D-serine, could be used as a therapeutic agent in the treatment of schizophrenia-related symptoms.

Humour experience in schizophrenia: relationship with executive dysfunction and psychosocial impairment

BACKGROUND

The ability to appreciate humour is essential to successful human interactions. In this study, we hypothesized that individuals with schizophrenia would have diminished ability to recognize and appreciate humour. The relationship between humour experience and clinical symptoms, cognitive and social functioning was examined.

METHOD

Thirty patients with a DSM-IV diagnosis of schizophrenia were compared with 30 age-, gender-, IQ- and ethnicity-matched healthy controls. Humour recognition was measured by identification of humorous moments in four silent slapstick comedy film clips and calculated as d-prime (d') according to signal detection theory. Humour appreciation was measured by self-report mood state and funniness ratings. Patients were assessed for clinical symptoms, theory of mind ability, executive function [using the Wisconsin Card Sorting Test (WCST)] and social functioning [using the Life Skills Profile (LSP)].

RESULTS

Patient and control groups did not differ in the funniness ratings they attributed to the video clips. Patients with schizophrenia had a lower d' (humour) compared to the controls, after controlling for (1) the performance of a baseline recognition task with a non-humorous video clip and (2) severity of depressive symptoms. In patients, d' (humour) had significant negative correlation with delusion and depression scores, the perseverative error score of the WCST and the total scores of the LSP.

CONCLUSIONS

Compared with controls, patients with schizophrenia were less sensitive at detecting humour but similarly able to appreciate humour. The degree of humour recognition difficulty may be associated with the extent of executive dysfunction and thus contribute to the psychosocial impairment in patients with schizophrenia.

Perceptual organization by proximity and similarity in schizophrenia

Perceptual organization represents a basic and essential function that occurs at an intermediate level of visual processing. Much of the previous research on perceptual organization in schizophrenia employed indirect measurements, or included factors beyond sensory processing. The aims of the present study were to determine the integrity of perceptual organization in schizophrenia, as well as to determine the stimulus duration necessary to perform perceptual organization. Psychophysical measurements were compared between patients with schizophrenia and matched control subjects. Participants viewed dot patterns briefly presented on a computer monitor, and indicated whether stimuli appeared grouped as vertical or horizontal lines. Grouping was based upon either relative proximity or similarity in color. Across trials, relative proximity or color similarity was progressively reduced until stimuli became bi-stable (perceived as either of two patterns of grouping), establishing the grouping threshold. In separate conditions, stimuli were immediately followed by a mask to limit processing. Stimulus duration was progressively reduced until stimuli became bi-stable, establishing the critical stimulus duration (CSD). Schizophrenia patients demonstrated elevated grouping thresholds for grouping by proximity as well as color similarity. In addition, CSD was significantly extended for the schizophrenia group, with a nearly four-fold increase in duration of processing. These results provide direct evidence of impairment in schizophrenia for perceptual organization based upon spatial relationships and feature similarity, and suggest deficits in low-level perceptual organization processes. Although this study did not directly investigate the physiological correlates underlying perceptual impairments, these results are consistent with a theory of impaired lateral connections within visual cortical areas in schizophrenia.

Deficient attentional modulation of startle eyeblink is associated with symptom severity in the schizophrenia spectrum

Patients with schizophrenia-spectrum disorders show deficient prepulse inhibition (PPI) of the startle eyeblink reflex which is thought to reflect an early stage of information processing called automatic sensorimotor gating. They also exhibit deficient attentional modulation of PPI and prepulse facilitation (PPF) of startle which is thought to reflect deficient early and later controlled attentional processing. This is the first study to assess attentional modulation of PPI and PPF in a 3-group schizophrenia-spectrum sample of age- and sex-matched unmedicated schizotypal personality disorder (SPD) and schizophrenia patients, and healthy controls. Participants performed a tone-length judgment task involving attended, ignored, and novel tone prepulses while the acoustic startle eyeblink reflex was measured. Healthy controls showed greater PPI and PPF during the attended prepulses compared with the ignored prepulses. In contrast, both the SPD and schizophrenia patient groups failed to show this pattern, indicating deficient early and later controlled attentional processing. These findings suggest abnormal attentional modulation of PPI and PPF may be a trait-like feature found in patients with schizophrenia-spectrum disorders. Among the schizophrenia-spectrum sample, more deficient PPI during the attended prepulses was associated with greater symptom severity as measured by the total 18-item Brief Psychiatric Rating Scale score.

Response selection in schizophrenia

Schizophrenia patients tend to have longer and more variable latencies of response than healthy control subjects. However, the distributions of data from the two groups overlap to a large extent. Therefore, we investigated (1) whether the process of response selection in schizophrenia patients is like that of slow control subjects or has different properties, and (2) whether the intra-individual variability of schizophrenia patients is intrinsically greater than that of control subjects or reflects their longer mean latency. To answer these questions we tested schizophrenia patients and healthy control subjects in a choice reaction time (RT) task with 2-choice and 4-choice conditions. We analyzed how mean RT in the 2-choice condition predicted mean RT in the 4-choice condition and found that the relation was significantly different between the two groups. In contrast, the intra-individual variability of RT was related to mean RT in the same way for schizophrenia patients and control subjects. These results indicate that the response selection process of schizophrenia patients was not simply a slower version of the same process engaged by control subjects, but it was a selection process with different dynamic properties. In contrast, schizophrenia patients did not have a greater intrinsic variability than control subjects. Furthermore, we found that the difference Deltat between RT measured in the 4-choice condition and RT predicted for the control group in the same condition could be used to discriminate effectively patients and control subjects. However, there was no significant association between Deltat and clinical variables. These results suggest that Deltat could reflect a trait impairment of schizophrenia independent from symptom profile. Finally, we suggest that the impairment of the process of selection of the motor response in schizophrenia reflects the alteration of the time-dependent patterns of neural activity that result from anomalies in the connectivity of the brain areas engaged for the selection of the motor response.

Positive and Negative Spatial Priming in Schizophrenia

Priming tasks are used for investigating the deficits of selective attention in schizophrenia, which are thought to be related to the psychotic symptoms. Priming was assessed in acutely psychotic unmedicated (n = 22) and medicated (n = 36) schizophrenia patients and in control subjects (n = 42). The subjects had to indicate the location of a target stimulus in two consecutive stimulus displays (prime and probe). Each stimulus appeared together with a distractor on a screen. Negative Priming is characterized by an increase in reaction time, whenever a probe target is presented at a prime distractor location. Positive Priming is characterized by a decrease in reaction time, when the probe target is presented at the prime target location. Schizophrenia patients altogether showed no abnormalities in priming effects, neither in the acute phase of illness (medicated and unmedicated) nor in partial remission (one month later, medicated). In unmedicated patients however Negative Priming was inversely correlated with the severity of positive symptoms. This indicates a priming deficit in a small subgroup of severely ill patients. The data support the notion that automatic (implicit) mechanisms of learning are unimpaired in schizophrenia patients unless symptoms exceed a certain critical level.

The endophenotype concept in psychiatric genetics

The idea that some phenotypes bear a closer relationship to the biological processes that give rise to psychiatric illness than diagnostic categories has attracted considerable interest. Much effort has been devoted to finding such endophenotypes, partly because it is believed that the genetic basis of endophenotypes will be easier to analyse than that of psychiatric disease. This belief depends in part on the assumption that the effect sizes of genetic loci contributing to endophenotypes are larger than those contributing to disease susceptibility, hence increasing the chance that genetic linkage and association tests will detect them. We examine this assumption by applying meta-analytical techniques to genetic association studies of endophenotypes. We find that the genetic effect sizes of the loci examined to date are no larger than those reported for other phenotypes. A review of the genetic architecture of traits in model organisms also provides no support for the view that the effect sizes of loci contributing to phenotypes closer to the biological basis of disease is any larger than those contributing to disease itself. While endophenotype measures may afford greater reliability, it should not be assumed that they will also demonstrate simpler genetic architecture.

Early visual information processing deficit in depression with and without Borderline Personality Disorder

Backward masking is a measure of early visual information processing usually abnormal in psychotic disorders. Previous studies of subjects with Borderline Personality Disorder have been inconsistent regarding their impairment or lack of impairment on backward masking. We examined visual backward masking performance in samples of unmedicated depressed patients with (n=12) and without (n=16) Borderline Personality Disorder, and healthy volunteers (n=18). Accuracy was poorer in depressed BPD patients, relative to both non-BPD depressed and healthy comparison subjects. As in previous studies, no differences in accuracy were found between non-BPD depressed patients and healthy comparison subjects. Differences in BPD subjects' accuracy were most evident at the fastest ISI and were not attributable to intercurrent psychotic symptoms. Beyond these group differences, accuracy at faster ISI's correlated with self-ratings of impulsiveness in all patients, and may be a general correlate of this trait. Poor early information processing appears to be a feature of Borderline Personality Disorder, and may play a role in the impulsive behavior that is characteristic of the disorder.

A new dimension of sensory dysfunction: stereopsis deficits in schizophrenia

BACKGROUND

Schizophrenia is a neurocognitive disorder with a wide range of cognitive and sensory impairments. Early visual processing has been shown to be especially impaired. This article investigates the integrity of binocular depth perception (stereopsis) in schizophrenia.

METHODS

Seventeen schizophrenia patients and 19 healthy control subjects were compared on the Graded Circles Stereo Test. Results of stereoacuity were compared between patients and control subjects using t test.

RESULTS

Schizophrenia patients demonstrated significantly (p = .006) reduced stereoacuity (mean = 142 arcseconds) versus control subjects (mean = 55 arcseconds). At the normative level for adults, patients performed below chance.

CONCLUSIONS

These findings demonstrate an impairment of binocular depth perception and further confirm deficits of early visual processing in schizophrenia. Findings are discussed in context of magnocellular/dorsal stream processing with implications for visual processing and cognitive deficits.

Weakened center-surround interactions in visual motion processing in schizophrenia

Schizophrenia is often accompanied by a range of visual perception deficits, with many involving impairments in motion perception. The presence of perceptual abnormalities may impair neural processes that depend on normal visual analysis, which in turn may affect overall functioning in dynamic visual environments. Here, we examine the integrity of suppressive center-surround mechanisms in motion perception of schizophrenic patients. Center-surround suppression has been implicated in a range of visual functions, including figure-ground segregation and pursuit eye movements, visual functions that are impaired in schizophrenia. In control subjects, evidence of center-surround suppression is found in a reduced ability to perceive motion of a high-contrast stimulus as its size increases. This counterintuitive finding is likely a perceptual correlate of center-surround mechanisms in cortical area MT. We now show that schizophrenic patients exhibit abnormally weak center-surround suppression in motion, an abnormality that is most pronounced in patients with severe negative symptoms. Interestingly, patients with the weakest surround suppression outperformed control subjects in motion discriminations of large high-contrast stimuli. This enhanced motion perception of large high-contrast stimuli is consistent with an MT abnormality in schizophrenia and has a potential to disrupt smooth pursuit eye movements and other visual functions that depend on unimpaired center-surround interactions in motion.

Subcortical visual dysfunction in schizophrenia drives secondary cortical impairments

Visual processing deficits are an integral component of schizophrenia and are sensitive predictors of schizophrenic decompensation in healthy adults. The primate visual system consists of discrete subcortical magnocellular and parvocellular pathways, which project preferentially to dorsal and ventral cortical streams. Subcortical systems show differential stimulus sensitivity, while cortical systems, in turn, can be differentiated using surface potential analysis. The present study examined contributions of subcortical dysfunction to cortical processing deficits using high-density event-related potentials. Event-related potentials were recorded to stimuli biased towards the magnocellular system using low-contrast isolated checks in Experiment 1 and towards the magnocellular or parvocellular system using low versus high spatial frequency (HSF) sinusoidal gratings, respectively, in Experiment 2. The sample consisted of 23 patients with schizophrenia or schizoaffective disorder and 19 non-psychiatric volunteers of similar age. In Experiment 1, a large decrease in the P1 component of the visual event-related potential in response to magnocellular-biased isolated check stimuli was seen in patients compared with controls (F = 13.2, P = 0.001). Patients also showed decreased slope of the contrast response function over the magnocellular-selective contrast range compared with controls (t = 9.2, P = 0.04) indicating decreased signal amplification. In Experiment 2, C1 (F = 8.5, P = 0.007), P1 (F = 33.1, P < 0.001) and N1 (F = 60.8, P < 0.001) were reduced in amplitude to magnocellular-biased low spatial frequency (LSF) stimuli in patients with schizophrenia, but were intact to parvocellular-biased HSF stimuli, regardless of generator location. Source waveforms derived from inverse dipole modelling showed reduced P1 in Experiment 1 and reduced C1, P1 and N1 to LSF stimuli in Experiment 2, consistent with surface waveforms. These results indicate pervasive magnocellular dysfunction at the subcortical level that leads to secondary impairment in activation of cortical visual structures within dorsal and ventral stream visual pathways. Our finding of early visual dysfunction is consistent with and explanatory of classic literature showing subjective complaints of visual distortions and is consistent with early visual processing deficits reported in schizophrenia. Although deficits in visual processing have frequently been construed as resulting from failures of top-down processing, the present findings argue strongly for bottom-up rather than top-down dysfunction at least within the early visual pathway. Deficits in magnocellular processing in this task may reflect more general impairments in neuronal systems functioning, such as deficits in non-linear amplification and may thus represent an organizing principle for predicting neurocognitive dysfunction in schizophrenia.

Dysregulation of thalamic sensory "transmission" in schizophrenia: neurochemical vulnerability to hallucinations

Cholinergic arousal mechanisms predispose thalamic and cortical neurons to fire action potentials at gamma rhythms, which have a tendency to resonate in thalamocortical networks, thereby forming coherent assemblies under constraints of sensory input to specific thalamic nuclei, on the one hand, and prefrontal and limbic attentional mechanisms, on the other. Perception may be based on sustained assemblies of coherent gamma oscillations in thalamocortical circuits. In schizophrenia, the impact of sensory input on self-organization of thalamocortical activity may be generally reduced. As a result, processes underlying perception can become uncoupled from sensory input, particularly at times of hyperarousal, leading to domination of attentional mechanisms and the emergence of hallucinations. Evidence is reviewed that implicates excessive neuronal noise in specific thalamic nuclei in the generation of hallucinations in schizophrenia. Nicotinic receptor abnormalities, dopaminergic hyperactivity and glutamate-receptor hypofunction are reconciled within a model of psychotic symptom generation that places crucial emphasis on dysfunction of the reticular thalamic nucleus.

Self-initiated encoding facilitates object working memory in schizophrenia: implications for the etiology of working memory deficit

BACKGROUND

Working memory (WM) deficit is present in a majority of patients with schizophrenia but it is unclear which components of WM are impaired. Past studies suggest that encoding may be compromised. One important determinant of encoding is the deployment of selective attention to the target stimulus. In addition, attention and encoding are modulated by motivational factors. In this study, we investigated the effects of self-initiated encoding (i.e., voluntary attention) on WM.

METHODS

19 patients with schizophrenia and 19 matched control subjects participated in visual WM and control tasks. Encoding was manipulated by asking subjects to select from two face targets and memorize 1) one of the two identical faces (Non-preference condition), 2) one that is marked (Non-choice condition), and 3) one they prefer (Preference condition). WM accuracy for both location (spatial) and identity (object) was measured.

RESULTS

Overall, patients with schizophrenia were less accurate and slower than the control subjects but the deficit was greater for object WM. However, patients were more accurate in object WM when they selected a preferred face as their target during encoding (preference condition) compared with the other two conditions. This effect was not significant for spatial WM.

CONCLUSIONS

These results suggest that voluntary, self-initiated attention may facilitate object encoding especially if the selection of the target involves affective choice, and that attention may play different roles in encoding 'what' versus 'where' in WM. Since encoding affects all forms of memory, these results may have a more general implication for memory.

Does negative symptom change relate to neurocognitive change in schizophrenia? Implications for targeted treatments

Negative symptoms and cognitive dysfunction are among the most challenging obstacles in the treatment of schizophrenia. It is unknown to what extent they are overlapping or independent disease processes. In the search for targeted treatments of negative symptoms and cognitive impairments, it is imperative to determine their longitudinal relationship. 267 stable outpatients with schizophrenia in a work and cognitive rehabilitation program were evaluated using symptom measures and a comprehensive neuropsychological test battery at baseline and at the conclusion of rehabilitation, 6 months later. Baseline negative symptom, neuropsychological variables and change scores from intake to follow-up on these variables were correlated. These analyses were repeated with a subsample (n = 161) who had clinically significant negative symptoms at baseline. ANCOVA's were performed to compare patients whose negative symptoms improved by 5 points or more (n = 69) with those whose negative symptoms got worse by 5 points or more (n = 26) on their neurocognitive performance at follow-up. Intake negative symptoms were significantly associated with theory of mind and visuomotor processing. Results failed to support a lawful relationship between change in negative symptoms and neurocognition. These findings suggest that negative symptoms and neurocognition should be viewed as relatively independent targets for intervention.

An investigation of semantic priming in schizophrenia using a new priming paradigm

In the present study, twenty schizophrenic patients and twenty healthy controls were tested in a new priming paradigm that allows a clear distinction to be made between automatic, perceptual priming effects and effects related to decision bias. Participants had to identify briefly presented masked target words preceded by clearly visible primes that were semantically related to the target or not. Target presentation duration corresponded to a pre-determined perceptual threshold for each participant, and a two-alternative forced-choice methodology was used. Equivalent amounts of semantic priming were found in schizophrenic patients compared with healthy controls. However, for the schizophrenic patients, a positive correlation was found between the size of automatic perceptual priming effects and formal thought disorders, as measured by Andreasen's Thought, Language and Communication (TLC) scale. The new paradigm tested in the present study overcomes some of the limitations of prior research on semantic priming in schizophrenia, and provides further evidence suggesting that an increased spreading of activation in the semantic network could partly underlie formal thought disorders in schizophrenia.

The use of neurophysiological endophenotypes to understand the genetic basis of schizophrenia

Specifying the complex genetic architecture of the “fuzzy” clinical phenotype of schizophrenia is an imposing problem. Utilizing metabolic, neurocognitive, and neurophysiological “intermediate” endophenotypic measures offers significant advantages from a statistical genetics stand-point. Endophenotypic measures are amenable to quantitative genetic analyses, conferring upon them a major methodological advantage compared with largely qualitative diagnoses using the Diagnostic and Statistical Manual of Mental Health, 4th Edition (DSM-IV). Endophenotypic deficits occur across the schizophrenia spectrum in schizophrenia patients, schizotypal patients, and clinically unaffected relatives of schizophrenia patients, Neurophysiological measures, such as P50 event-related suppression and the prepulse inhibition (PPI) of the startle response, are endophenotypes that can be conceptualized as being impaired because of a single genetic abnormality in the functional cascade of DNA to RNA to protein. The “endophenotype approach” is also being used to understand other medical disorders, such as colon cancer, hemochromatosis, and hypertension, where there is interplay between genetically conferred vulnerability and nongenetic stressors. The power and utility of utilizing endophenotypes to understand the genetics of schizophrenia is discussed in detail in this article.

Impairments in generation of early-stage transient visual evoked potentials to magno- and parvocellular-selective stimuli in schizophrenia

OBJECTIVE

Patients with schizophrenia demonstrate significant impairments of early visual processing, potentially implicating dysfunction of the magnocellular visual pathway. The present study evaluates transient visual evoked potential (tVEP) responses to stimuli biased toward the magnocellular (M) or parvocellular (P) systems in patients with schizophrenia vs. normal volunteers first to evaluate relative contributions of M and P systems to specific tVEP components in schizophrenia and, second, to evaluate integrity of early M and P processing in schizophrenia.

METHODS

Seventy-four patients with schizophrenia and schizoaffective disorder were compared with 59 control subjects using separate stimuli to assess the tVEP response to M, P and mixed M/P conditions. Stimuli were biased toward M vs. P processing by manipulation of chromatic and achromatic contrast. C1, P1, N1 and P2 components were compared between patients and controls. All subjects showed 20/32 vision or better.

RESULTS

Waveforms were obtained to low contrast (M), chromatic contrast (P) and high contrast (mixed M/P) stimuli in both patients and controls. C1 was present to P and mixed M/P stimuli. Patients showed a significant reduction in amplitude and an increase in latency of the C1 component. P1 was elicited primarily by M and mixed M/P stimuli, whereas N1 was elicited primarily by P and mixed M/P stimuli. Patients showed reductions in both P1 and N1 amplitudes across conditions. However, only reductions in P1 amplitude survived covariation for between group differences in visual acuity. Further, P1 amplitude reductions in the M condition correlated with a proxy measure of global outcome.

CONCLUSIONS

M- and P-selective stimuli elicit differential components of the tVEP. Patients with schizophrenia show significant reductions in response even to simple visual stimuli. Deficits, particularly within the M system, may correlate significantly with global outcome and level of community functioning.

SIGNIFICANCE

Whereas deficits in high-order cognitive processing have been extensively documented in schizophrenia, integrity of early-stage sensory processing has been studied to a lesser degree. The present findings suggest that deficits in early-stage visual processing are significantly related to overall clinical outcome in schizophrenia. Further, between-group differences in visual acuity may influence VEP results, even for subjects with 'normal' vision (20/32 or better).