Spatial working memory: absence of gender differences in schizophrenia patients and healthy control subjects

Sex Differences in Cognition in Schizophrenia: What We Know and What We Do Not Know

Cognitive impairment is a core feature of schizophrenia. This selective review examines whether schizophrenia patients show preserved sexual dimorphism in cognition. Existing studies using performance tasks largely show comparable sex effects between schizophrenia patients and healthy populations. This pattern appears to be similar across multiple cognitive domains and across phase of illness. Our selective review also identifies several unresolved questions about sex differences in cognition in schizophrenia. A better understanding of sex differences in cognition in schizophrenia may provide important clues to probing the relationship between cognitive impairment and pathophysiological processes of the disorder.

A genome-wide association study identified one variant associated with static spatial working memory in Chinese population

Spatial working memory (SWM) is a kind of memory that temporarily preserves spatial information (the location or order of objects, etc.). Individuals with mental disorders tend to show worse performance in SWM task. This study investigated the genetic basis of two subtypes of SWM, static spatial working memory (SSWM) and dynamic spatial working memory (DSWM) in humans, using quantitative genomic analyses. A total of 451 Chinese students were tested on their magnitudes of SSWM and DSWM. A genome-wide association study (GWAS) was performed. Two SNPs (top SNP: rs80263879, p = 1.6 × 10−9, gene: epoxide hydrolase 2, EPHX2) reaching genome-wide significance for SSWM were identified. There is a high linkage disequilibrium between these two SNPs. The data of expression quantitative trait locus (eQTL) showed that different genotypes of rs80263879 and rs72478903 made significant differences in the expression of EPHX2 gene in the spinal cord (p = 0.022, p = 0.048). Enrichment analysis identified a gene set significantly associated with DSWM. Overall, our study discovered a candidate genetic locus and gene set for the genetics of the SWM.

Refining the Empirical Constraints on Computational Models of Spatial Working Memory in Schizophrenia

BACKGROUND

Impairments in spatial working memory (sWM) have been well documented in schizophrenia. Here we provide a comprehensive test of a microcircuit model of WM performance in schizophrenia that predicts enhanced effects of increasing delay duration and distractors based on a hypothesized imbalance of excitatory and inhibitory processes.

METHODS

Model predictions were tested in 41 people with schizophrenia (PSZ) and 32 healthy control subjects (HCS) performing an sWM task. In one condition, a single target location was followed by delays of 0, 2, 4, or 8 seconds. In a second condition, distractors were presented during the 4-second delay interval at 20°, 30°, 40°, 50°, or 90° from the original target location.

RESULTS

PSZ showed less precise sWM representations than HCS, and the rate of memory drift over time was greater in PSZ than in HCS. Relative to HCS, the spatial recall responses of PSZ were more repelled by distractors presented close to the target location and more attracted by distractors presented far from the target location. The degree of attraction to distant distractors was correlated with the rate of memory drift in the absence of distractors.

CONCLUSIONS

Consistent with the microcircuit model, PSZ exhibited both a greater rate of drift and greater attraction to distant distractors relative to HCS. These two effects were correlated, consistent with the proposal that they arise from a single underlying mechanism. However, the repulsion effects produced by nearby distractors were not predicted by the model and thus require an updated modeling framework.

Visual-spatial processing and dimensions of schizophrenia: a preliminary study on 62 schizophrenic subjects

The aim of the study was to explore the relationships between the performance in figure-ground segregation and the clinical dimensions in schizophrenia. Sixty-two schizophrenic subjects filled out the embedded figures test (EFT) and the schizophrenic symptomatology was rated using the brief psychiatric rating scale (BPRS). The BPRS items were grouped into four categories: positive, negative, general and disorganization. The results showed in male schizophrenics negative and significant correlations between EFT scores and negative or disorganization subscales. Taken into account that in schizotypic subjects EFT scores was negatively correlated with negative dimension of schizotypy we suggested that those relationship could constitute a trait of the disease.

Sex differences in visual-spatial working memory: A meta-analysis

Visual-spatial working memory measures are widely used in clinical and experimental settings. Furthermore, it has been argued that the male advantage in spatial abilities can be explained by a sex difference in visual-spatial working memory. Therefore, sex differences in visual-spatial working memory have important implication for research, theory, and practice, but they have yet to be quantified. The present meta-analysis quantified the magnitude of sex differences in visual-spatial working memory and examined variables that might moderate them. The analysis used a set of 180 effect sizes from healthy males and females drawn from 98 samples ranging in mean age from 3 to 86 years. Multilevel meta-analysis was used on the overall data set to account for non-independent effect sizes. The data also were analyzed in separate task subgroups by means of multilevel and mixed-effects models. Results showed a small but significant male advantage (mean d = 0.155, 95 % confidence interval = 0.087-0.223). All the tasks produced a male advantage, except for memory for location, where a female advantage emerged. Age of the participants was a significant moderator, indicating that sex differences in visual-spatial working memory appeared first in the 13-17 years age group. Removing memory for location tasks from the sample affected the pattern of significant moderators. The present results indicate a male advantage in visual-spatial working memory, although age and specific task modulate the magnitude and direction of the effects. Implications for clinical applications, cognitive model building, and experimental research are discussed.

Sex differences in the neural substrates of spatial working memory during adolescence are not mediated by endogenous testosterone

Adolescence is a developmental period characterized by notable changes in behavior, physical attributes, and an increase in endogenous sex steroid hormones, which may impact cognitive functioning. Moreover, sex differences in brain structure are present, leading to differences in neural function and cognition. Here, we examine sex differences in performance and blood oxygen level-dependent (BOLD) activation in a sample of adolescents during a spatial working memory (SWM) task. We also examine whether endogenous testosterone levels mediate differential brain activity between the sexes. Adolescents between ages 10 and 16 years completed a SWM functional magnetic resonance imaging (fMRI) task, and serum hormone levels were assessed within seven days of scanning. While there were no sex differences in task performance (accuracy and reaction time), differences in BOLD response between girls and boys emerged, with girls deactivating brain regions in the default mode network and boys showing increased response in SWM-related brain regions of the frontal cortex. These results suggest that adolescent boys and girls adopted distinct neural strategies, while maintaining spatial cognitive strategies that facilitated comparable cognitive performance of a SWM task. A nonparametric bootstrapping procedure revealed that testosterone did not mediate sex-specific brain activity, suggesting that sex differences in BOLD activation during SWM may be better explained by other factors, such as early organizational effects of sex steroids or environmental influences. Elucidating sex differences in neural function and the influence of gonadal hormones can serve as a basis of comparison for understanding sexually dimorphic neurodevelopment and inform sex-specific psychopathology that emerges in adolescence.

Memory-guided saccades in youth-onset psychosis and attention deficit hyperactivity disorder (ADHD)

AIM

Working memory deficits have been shown to be present in children and adolescents with schizophrenia and attention deficit hyperactivity disorder. Considering the differences in clinical characteristics between these disorders, it was the goal of this study to assess differences in the specific components of working memory in children and adolescents with psychosis and attention deficit hyperactivity disorder.

METHODS

Children and adolescents (age range 8-20 years) with either a non-affective psychotic disorder (n = 25), attention deficit hyperactivity disorder (n = 33) and controls (n = 58) were administered an oculomotor delayed-response task using both a recall and a control condition. Memory-guided saccades were measured during delay periods of 2, 8 and 20 s.

RESULTS

Although both clinical groups were less accurate than controls, there was no evidence of a disproportionate impairment in recall. In addition, there was no evidence of a delay-dependent impairment in psychosis; however, there was a delay-dependent impairment in attention deficit hyperactivity disorder when corrective saccades were included. Speed of information processing was correlated with distance errors in psychosis, suggesting that speed of encoding the stimulus location may have constrained the accuracy of the saccades.

CONCLUSIONS

Our findings support impairments during encoding in the psychosis group and a delay-dependent deficit in the attention deficit hyperactivity disorder group.

Comparing the influences of age and disease on the Brief Assessment of Cognition in Schizophrenia in Japanese patients with schizophrenia

BACKGROUND

The Brief Assessment of Cognition in Schizophrenia (BACS) is an evaluation of cognitive function that can be completed with more cases. However, there are few studies that compare which factor, disease or aging, is a better determinant of performance on the BACS. The present study aimed to investigate the influences of disease and aging on BACS performance in schizophrenic patients using subjects with a wide range of ages.

METHODS

Schizophrenic patients (n = 165) and a comparison group (n = 171) were recruited as subjects. All participants completed the Japanese language version of the BACS (BACS-J), and the influences of disease and aging on performance in the BACS were examined with the use of multiple regression analysis.

RESULTS

There was a significant influence of diagnosis and level of education on all six tasks of the BACS and the performance and composite scores. In addition, age was found to influence five tasks and the composite score, the duration of illness influenced four tasks and the composite score, and gender influenced one task and the composite score.

CONCLUSION

The present study suggests that performance on the BACS was impaired not only by disease but also by level of education and aging.

The effects of PRX-07034, a novel 5-HT6 antagonist, on cognitive flexibility and working memory in rats

RATIONALE

Accumulating evidence indicates that schizophrenia and autism spectrum disorder patients are marked by cognitive deficits in working memory and strategy switching. There is accumulating evidence that 5-hydroxytryptamine (5-HT)(6) receptors may serve as a useful target to improve cognitive functioning.

OBJECTIVES

In the present experiments, the novel 5-HT(6) antagonist, PRX-07034, was examined for its selectivity of the 5-HT(6) receptor, as well as its effect on delayed spontaneous alternation and strategy switching.

METHODS

The binding affinity of PRX-07034 to the 5-HT(6) receptor, other 5-HT receptors, as well as other G-protein coupled receptors, ion channels, and transporters was evaluated. Cyclic AMP production was measured from transfected HEK-293 cells. In separate behavioral experiments, rats received different doses of PRX-07034 (0.1, 1, or 3 mg/kg, i.p.) 30 min prior to delayed spontaneous alternation testing or prior to the acquisition and switch phases in a place-response switch test.

RESULTS

The results indicated that PRX-07034 is both a potent (Ki = 4-8 nM) and highly selective 5-HT(6) receptor antagonist (≥100-fold selectivity for the 5-HT(6) receptor compared to 68 other GPCRs, ion channels, and transporters, except D(3) (Ki = 71 nM) and 5-HT(1B) (Ki = 260 nM) receptors. For cyclic AMP quantification, PRX-07034 demonstrated antagonist activity (IC(50) = 19 nM) without an effect on basal levels and did not show any agonist activity up to 10 μM. PRX-07034 at 1 and 3 mg/kg (but not 0.1 mg/kg) significantly enhanced delayed spontaneous alternation. The drug at 1 and 3 mg/kg also enhanced switching between a place and response strategy, but did not affect initial learning of either a place or response discrimination.

CONCLUSIONS

These findings demonstrate that PRX-07034 is a selective 5-HT(6) receptor antagonist that may represent a novel treatment for enhancing working memory and cognitive flexibility.

Aberrant visual circuitry associated with normal spatial match-to-sample accuracy in schizophrenia

A goal of this study was to evaluate the function of the anterior cingulate cortex (ACC) and of the dorsolateral prefrontal cortex (DLPFC) in medicated patients with schizophrenia (SZ), a small group of first-degree relatives, and healthy controls using a visual delayed match-to-sample task in conjunction with functional magnetic resonance imaging (fMRI). To mitigate performance differences between SZ and healthy controls, we used a novel task that allows for individualized adjustment of task difficulty to match ability level. We also trained participants on the task prior to scanning. Using an event-related design, we modeled three components of the match-to-sample trial: visual encoding, delay, and discrimination. We did not find significant differences in ACC/medial frontal cortex activation between the groups. However, compared to healthy controls, SZ showed decreased activation in visual processing areas during the encoding and discrimination phases of the task and in the ventrolateral prefrontal cortex during the delay. These findings emphasize the tendency of schizophrenia subjects to solve perceptual memory problems by engaging diverse regions.

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.

Absence of established sex differences in patients with schizophrenia on a two-dimensional object array task

Sex differences are pervasive in schizophrenia, ranging from differences in the age of onset and symptoms of the illness to structural brain differences. Yet, there has been very little research on the interaction of these differences with established cognitive sex differences that exist in healthy populations. We tested 25 patients with schizophrenia and 17 healthy controls on a two-dimensional task of object location memory. It has been previously shown that healthy females outperform healthy males on this task, a result that was upheld in this experiment. However, the female advantage is completely absent in patients with schizophrenia. This finding has important implications for the interpretation of clinical and physiological sex differences present in schizophrenia.

Endophenotypes in schizophrenia: a selective review

BACKGROUND

Given the wealth of data in the literature on schizophrenia endophenotypes, it is useful to have one source to reference their frequency data. We reviewed the literature on disease-liability associated variants in structural and functional magnetic resonance images (MRI), sensory processing measures, neuromotor abilities, neuropsychological measures, and physical characteristics in schizophrenia patients (SCZ), their first-degree relatives (REL), and healthy controls (HC). The purpose of this review was to provide a summary of the existing data on the most extensively published endophenotypes for schizophrenia.

METHODS

We searched PubMed and MedLine for all studies on schizophrenia endophenotypes comparing SCZ to HC and/or REL to HC groups. Percent abnormal values, generally defined as >2 SD from the mean (in the direction of abnormality) and/or associated effect sizes (Cohen's d) were calculated for each study.

RESULTS

Combined, the articles reported an average 39.4% (SD=20.7%; range=2.2-100%) of abnormal values in SCZ, 28.1% (SD=16.6%; range=1.6-67.0%) abnormal values in REL, and 10.2% (SD=6.7%; range=0.0-34.6%) in HC groups.

CONCLUSIONS

These findings are reviewed in the context of emerging hypotheses on schizophrenia endophenotypes, as well as a discussion of clustering trends among the various intermediate phenotypes. In addition, programs for future research are discussed, as instantiated in a few recent large-scale studies on multiple endophenotypes across patients, relatives, and healthy controls.

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.

Hemispheric asymmetry and callosal integration of visuospatial attention in schizophrenia: a tachistoscopic line bisection study

BACKGROUND

A hallmark of visuospatial neglect syndrome is that patients with lesions to right parietal cortex misbisect horizontal lines far rightward of veridical center. Neurologically normal subjects misbisect lines with a systematic leftward bias (pseudoneglect). Both phenomena, as well as neuroimaging studies, disclose a predominant right-hemisphere control of spatial attention. Numerous studies of patients with schizophrenia have implicated global deficits of either right or left hemisphere function, as well as compromised integrity of the corpus callosum.

METHODS

To better understand the functional implications of schizophrenia we utilized a forced-choice tachistoscopic line bisection task to probe the status of right-hemisphere control of spatial attention, and compared left- versus right-hand unimanual responses to index the degree of callosal transfer of visuospatial information in both patient and control groups.

RESULTS

In contrast to the significant leftward bisection errors of control subjects, patients exhibit no significant leftward error. Whereas control subjects evince a significant correlation between left- and right-hand bisection errors, patients lack a significant intermanual correlation.

CONCLUSIONS

The lack of significant leftward bisection error of patients implies a deficit of right-hemisphere function. The lack of a significant correlation between left- and right-hand bisection errors in patients implies a loss of callosal integrity.

Working memory deficits in adults with ADHD: is there evidence for subtype differences?

BACKGROUND

Working memory performance is important for maintaining functioning in cognitive, academic and social activities. Previous research suggests there are prevalent working memory deficits in children with attention deficit hyperactivity disorder (ADHD). There is now a growing body of literature characterizing working memory functioning according to ADHD subtypes in children. The expression of working memory deficits in adults with ADHD and how they vary according to subtype, however, remains to be more fully documented.

METHODS

This study assessed differences in working memory functioning between Normal Control (NC) adults (N = 18); patients with ADHD, Combined (ADHD-CT) Type ADHD (N = 17); and ADHD, Inattentive (ADHD-IA) Type (N = 16) using subtests from the Wechsler Adult Intelligence Scale-III and Wechsler Memory Scale-III and the Paced Auditory Serial Addition Task (PASAT).

RESULTS

The ADHD groups displayed significant weaknesses in contrast to the NC group on working memory tests requiring rapid processing and active stimulus manipulation. This included the Letter-Number-Sequencing test of the Wechsler scales, PASAT omission errors and the longest sequence of consecutive correct answers on the PASAT. No overall ADHD group subtype differences emerged; however differences between the ADHD groups and the NC group varied depending on the measure and the gender of the participants. Gender differences in performance were evident on some measures of working memory, regardless of group, with males performing better than females.

CONCLUSION

In general, the data support a dimensional interpretation of working memory deficits experienced by the ADHD-CT and ADHD-IA subtypes, rather than an absolute difference between subtypes. Future studies should test the effects of processing speed and load on subtype performance and how those variables interact with gender in adults with ADHD.

Schizophrenia and rightward bias in line bisection

This study investigated line bisection in 10 males with schizophrenia and 15 controls. There was an overall leftward bias, consistent with slight right "pseudoneglect", but the schizophrenia group showed more variation with experimental conditions, suggesting impaired interhemispheric transfer. Specifically, the rightward bias was especially marked when the lines were positioned on the right side of the page, when the right hand was used, and when a right to left scan was adopted. The rightward bias was associated with the predominance of negative symptoms. Findings are discussed with reference to the role of the corpus callosum in the transfer of spatial attention.

The dual origin hypothesis: An evolutionary brain-behavior framework for analyzing psychiatric disorders

According to the dual origin hypothesis, the cerebral cortex of higher mammals evolved from two primordial brain structures, the amygdala and hippocampal formation. This developmental process defines the orderly principles of cortical connectivity and gives rise to functionally distinct ventral and dorsal systems within the cerebrum. This paper reviews the basic features of the dual origin theory. This model is then applied to understanding symptom production in a number of psychiatric illnesses, with particular reference to recent structural and functional imaging studies. In this paper I propose that psychiatric symptoms can be conceptualized as arising from abnormal processing within dorsal (time-space-motility) or ventral (meaning-motivation) systems, or from a disturbance in the functional interaction/balance between them. Within this framework, one can identify symptom-specific correlations that cross-traditional diagnostic boundaries, as well as potential mechanisms that may explain biologically valid diagnostic entities. Integrating evolutionary, connectional and functional bases across multiple species, the dual origin hypothesis offers a powerful neural systems model to help organize our understanding of psychiatric illness, therein suggesting novel approaches to diagnosis, prevention and treatment.

A longitudinal analysis of memory in patients with schizophrenia

Memory deficits are widely reported in patients with schizophrenia, but uncertainties remain about the extent and the longitudinal course of these deficits. Twenty-eight patients with a DSM-IV diagnosis of schizophrenia were tested on multiple aspects of memory at baseline, 9- and 18-month follow-up. Measures included: digit span, the Rivermead Behavioural Memory test (RBMT) battery, the Graded Naming Test (GNT) and several computerized memory tests from the Cambridge Automated Neuropsychological Testing Battery (CANTAB). A group of healthy controls (N=17) was tested on the CANTAB battery at baseline and 9-month follow up. The patients performed significantly poorer than controls on all CANTAB measures; however, there was no difference in change between groups over a 9-month period. Within-group patient comparisons revealed that symptoms reduced significantly over the study period, but had no association with memory. Significant improvements were observed for patients on two verbal memory tasks: the GNT and digit span, but not on any other measure. Interestingly, these were the only two tests on which patients were within normal limits at baseline. This study shows that patients with schizophrenia have deficits in multiple aspects of memory which remain stable over long periods of time. In addition, patients showed a tendency to improve on memory tasks which contained a verbal component.

A sex difference on a novel spatial working memory task in humans

Neurophysiological and behavioral evidence suggests that the prefrontal cortex (PFC) may be sexually differentiated in nonhuman primates. The present study examined whether there are sex differences in working memory in humans that might reflect sexual differentiation of human PFC. Male and female undergraduates were administered a novel multitrial spatial working memory task (SPWM) and a verbal working memory task. In three experiments, females committed significantly fewer working memory errors and took significantly less time to reach criterion than males on the SPWM task. The female advantage was not accounted for by differences in general intellectual ability, attention, perceptual speed, incidental memory, or speed of verbal access. In Study 3, a sex difference was also observed on a measure of verbal working memory. The findings suggest that some prefrontal functions may be sexually differentiated in humans.

Working memory in schizophrenia and mania: correlation with symptoms during the acute and subacute phases

OBJECTIVE

The aims of this study were to examine working memory in the acute subacute phase of schizophrenia and mania and to examine correlations between working memory and specific symptom domains.

METHOD

Visuospatial working memory and symptom profiles were assessed in three groups (schizophrenia group, n= 19; mania, n= 12; controls, n= 19) on two occasions separated by 4 weeks.

RESULTS

Both patient groups had significant deficits on working memory compared to the well controls and the schizophrenia and mania groups were equally impaired. All groups showed equivalent improvement over time. In the patient groups, impaired working memory was significantly correlated with the presence of both negative symptoms and positive thought disorder.

CONCLUSION

Impaired working memory is found in both schizophrenia and mania during the acute subacute phases. Further research is required in order to clarify the neurocognitive mechanisms linking impaired working memory with both negative symptoms and positive thought disorder.

The association between antisaccade task and working memory task performance in schizophrenia and bipolar disorder

To date, the research literature has yielded conflicting reports regarding the specificity of antisaccade deficits to schizophrenia. We sought to examine antisaccade and working memory task performance in schizophrenia patients and bipolar patients, as well as to examine the relationship between the two tasks in both patient populations. Thirty-four schizophrenia patients, 20 bipolar patients, and 30 nonpatient controls were administered saccadic inhibition (antisaccade), working memory, and sensorimotor tasks. Compared with the controls, the schizophrenia patients displayed both antisaccade deficits and working memory deficits. In contrast, the bipolar patients produced significantly more errors on the antisaccade task than the controls, though the bipolar group performed similarly to the control group on the working memory task. Mediational analyses demonstrated that working memory partially mediates the relationship between patients' diagnostic group status and antisaccade task performance; working memory performance contributed uniquely to the prediction of antisaccade task performance in the two patient groups. Antisaccade deficits do not appear specific to schizophrenia. The results suggest that in schizophrenia, working memory and antisaccade tasks are tapping similar cognitive processes, whereas in bipolar patients the processes underlying antisaccade and working memory performance are disparate.