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

Computational cognitive mechanisms of visual working memory in major depressive disorder and sex differences

This study examined the computational cognitive mechanisms of visual working memory (VWM) in MDD, focusing on memory precision while exploring potential sex differences. 159 Major Depressive Disorder (MDD) patients and 67 healthy controls (HC) completed the color delay estimation task to measure their VWM. The mainstream models of VWM were compared, and the variable-precision (VP) model was the best fit for our data. The Bayesian ANCOVA was used to compare the differences between groups (MDD & HC) and sexes (male & female). Results revealed that MDD had worse memory precision than HC (BF10 = 103.872, decisive evidence for H1). Specifically, they had larger resource allocation variability (BF10 = 19.421, strong evidence for H1), indicating that they distributed memory resources more unevenly across different items than HC. In addition, females had better memory precision than males (BF10 = 10.548, strong evidence for H1). More specifically, they had more initial resources during the color delay estimation task (BF10 = 6.003, substantial evidence for H1) than males. These findings highlight the critical role of diminished precision, specifically, larger resource allocation variability, in impaired VWM in MDD. Meanwhile, these findings highlight sex differences in memory precision and initial resources of VWM.

Effect of transcranial direct current stimulation with concurrent cognitive performance targeting posterior parietal cortex vs prefrontal cortex on working memory in schizophrenia: a randomized clinical trial

Working memory deficits are linked to irregularities in the dorsolateral prefrontal cortex (DLPFC) and the posterior parietal cortex (PPC) in schizophrenia, effective intervention strategies are lacking. We evaluated the differential efficacy and underlying neuromechanisms of targeting transcranial direct current stimulation (tDCS) at the DLPFC and the PPC with concurrent cognitive performance for working memory in schizophrenia. In a randomized and double-blind clinical trial, sixty clinically stable schizophrenic patients with below-average working memory were randomly assigned to active DLPFC, active PPC, and sham tDCS groups. Two sessions of tDCS during N-back task were delivered daily for five days. The primary outcome was changes in spatial span test scores from baseline to week 1. The secondary outcomes included changes in scores of color delay-estimation task, other cognitive tasks, and mismatch negativity (biomarker of N-methyl-d-aspartate receptor functioning). Compared with the active DLPFC group, the active PPC group demonstrated significantly greater improvement in spatial span test scores (p = 0.008, d = 0.94) and an augmentation in color delay-estimation task capacity at week 1; the latter sustained to week 2. Compared with the sham tDCS group, the active PPC group did not show a significant improvement in spatial span test scores at week 1 and 2; however, significant enhancement was observed in their color delay-estimation task capacity at week 2. Additionally, mismatch negativity amplitude was enhanced, and changes in theta band measures were positively correlated with working memory improvement in the active PPC group, while no such correlations were observed in the active DLPFC group or the sham tDCS group. Our results suggest that tDCS targeting the PPC relative to the DLPFC during concurrent cognitive performance may improve working memory in schizophrenia, meriting further investigation. The improvement in working memory appears to be linked to enhanced N-methyl-d-aspartate receptor functioning.

Discriminant analysis using MRI asymmetry indices and cognitive scores of women with temporal lobe epilepsy or schizophrenia

PURPOSE

This study aims to assess the diagnostic power of brain asymmetry indices and neuropsychological tests for differentiating mesial temporal lobe epilepsy (MTLE) and schizophrenia (SCZ).

METHODS

We studied a total of 39 women including 13 MTLE, 13 SCZ, and 13 healthy individuals (HC). A neuropsychological test battery (NPT) was administered and scored by an experienced neuropsychologist, and NeuroQuant (CorTechs Labs Inc., San Diego, California) software was used to calculate brain asymmetry indices (ASI) for 71 different anatomical regions of all participants based on their 3D T1 MR imaging scans.

RESULTS

Asymmetry indices measured from 10 regions showed statistically significant differences between the three groups. In this study, a multi-class linear discriminant analysis (LDA) model was built based on a total of fifteen variables composed of the most five significantly informative NPT scores and ten significant asymmetry indices, and the model achieved an accuracy of 87.2%. In pairwise classification, the accuracy for distinguishing MTLE from either SCZ or HC was 94.8%, while the accuracy for distinguishing SCZ from either MTLE or HC was 92.3%.

CONCLUSION

The ability to differentiate MTLE from SCZ using neuroradiological and neuropsychological biomarkers, even within a limited patient cohort, could make a substantial contribution to research in larger patient groups using different machine learning techniques.

Dense attention network identifies EEG abnormalities during working memory performance of patients with schizophrenia

Introduction

Patients with schizophrenia typically exhibit deficits in working memory (WM) associated with abnormalities in brain activity. Alterations in the encoding, maintenance and retrieval phases of sequential WM tasks are well established. However, due to the heterogeneity of symptoms and complexity of its neurophysiological underpinnings, differential diagnosis remains a challenge. We conducted an electroencephalographic (EEG) study during a visual WM task in fifteen schizophrenia patients and fifteen healthy controls. We hypothesized that EEG abnormalities during the task could be identified, and patients successfully classified by an interpretable machine learning algorithm.

Methods

We tested a custom dense attention network (DAN) machine learning model to discriminate patients from control subjects and compared its performance with simpler and more commonly used machine learning models. Additionally, we analyzed behavioral performance, event-related EEG potentials, and time-frequency representations of the evoked responses to further characterize abnormalities in patients during WM.

Results

The DAN model was significantly accurate in discriminating patients from healthy controls, ACC = 0.69, SD = 0.05. There were no significant differences between groups, conditions, or their interaction in behavioral performance or event-related potentials. However, patients showed significantly lower alpha suppression in the task preparation, memory encoding, maintenance, and retrieval phases F(1,28) = 5.93, p = 0.022, η2 = 0.149. Further analysis revealed that the two highest peaks in the attention value vector of the DAN model overlapped in time with the preparation and memory retrieval phases, as well as with two of the four significant time-frequency ROIs.

Discussion

These results highlight the potential utility of interpretable machine learning algorithms as an aid in diagnosis of schizophrenia and other psychiatric disorders presenting oscillatory abnormalities.

Peripheral Complement Factor-Based Biomarkers for Patients with First-Episode Schizophrenia

Objective

Schizophrenia (SCZ) is a severe, protracted neurological disorder that causes disruptive conduct in millions of individuals globally. Discovery of potential biomarkers in clinical settings would lead to the development of efficient diagnostic techniques and an awareness of the disease's pathogenesis and prognosis. The aim of the present study was to discover and identify serum complement factor-based biomarkers in discriminating patients with first-episode SCZ from healthy controls.

Methods

Eighty-nine patients with first-episode SCZ and 89 healthy controls were included in this study. Psychiatric symptom severity of patients with SCZ was measured with the Brief Psychiatric Rating Scale-18 Item Version (BPRS) and the Scales for the Assessment of Negative/Positive Symptoms (SANS/SAPS). A total of 5 complement factors including complement component 1 (C1), C2, C3, C4, and 50% hemolytic complement (CH50) were measured using commercially available enzyme-linked immunosorbent assay (ELISA) kits. The levels of serum complement factors in the SCZ and control groups were compared, and the receiver operating characteristic (ROC) curve method was used to assess the diagnostic values of various complement factors for separating SCZ patients from healthy controls. Pearson's correlation test was used to assess the relationships between serum complement factor concentrations and the psychiatric symptom severity.

Results

There was an increase in serum levels of C1, C2, C3, C4, and CH50 among patients with SCZ. Moreover, based on ROC curve analysis, the AUC value of a combined panel of C1, C2, C3, C4, and CH50 was 0.857 when used to discriminate patients with SCZ from healthy controls. Furthermore, serum C2, C3, and CH50 levels were positively correlated to the scores of SANS, SAPS, and BPRS in patients with SCZ, respectively.

Conclusion

These results suggested that circulating complement factors including C1, C2, C3, C4, and CH50 may have potential in discovering biomarkers for diagnosing first-episode SCZ.

Spatial and non-spatial feature binding impairments in visual working memory in schizophrenia

Working memory (WM) impairments are well recognized in schizophrenia patients (PSZ) and contribute to poor psycho-social outcomes in this population. Distinct neural networks underlay the ability to encode and recall visual and spatial information raising the possibility that profile of visual working memory performance may help pinpoint dysfunctional neural correlates in schizophrenia. This study assessed the resolution and associative aspects of visual working memory deficits in schizophrenia and whether these deficits arise during encoding or maintenance processes. A total of 60 participants (30 PSZ and 30 healthy controls) matched in age, gender and education assessed on a modified object in place (OiPT), a delayed non-match-to-sample (DNMST) and a delayed spatial estimation (DSET) task. Patients demonstrated lower accuracy than controls in binding visual features of the same object and recognizing novel objects as well as lower precision recalling the location of a memorized target. Moreover, response choice set size affected recognition accuracy more in PSZ than controls. However, delay duration affected spatial recall precisions, binding, and recognition accuracy equally in the two groups. Our results suggest that visual working memory (vWM) impairments in schizophrenia predominantly reflect spatial and non-spatial binding deficits, with largely preserved discrete feature information. Moreover, these impairments likely arise more during encoding than during maintenance. These binding deficits may reflect impaired effective neural functional connectivity observed in schizophrenia.

Awareness of the relative quality of spatial working memory representations

Working memory (WM) is the ability to maintain and manipulate information no longer accessible in the environment. The brain maintains WM representations over delay periods in noisy population-level activation patterns, resulting in variability in WM representations across items and trials. It is established that participants can introspect aspects of the quality of WM representations, and that they can accurately compare which of several WM representations of stimulus features like orientation or color is better on each trial. However, whether this ability to evaluate and compare the quality of multiple WM representations extends to spatial WM tasks remains unknown. Here, we employed a memory-guided saccade task to test recall errors for remembered spatial locations when participants were allowed to choose the most precise representation to report. Participants remembered either one or two spatial locations over a delay and reported one item's location with a saccade. On trials with two spatial locations, participants reported either the spatial location of a randomly cued item, or the location of the stimulus they remembered best. We found a significant improvement in recall error and increase in response time (RT) when participants reported their best-remembered item compared with trials in which they were randomly cued. These results demonstrate that participants can accurately introspect the relative quality of neural WM representations for spatial position, consistent with previous observations for other stimulus features, and support a model of WM coding involving noisy representations across items and trials.