Neural basis of the visual working memory deficit in schizophrenia: Merging evidence from fMRI and EEG

Simultaneous EEG-fMRI Investigation of Rhythm-Dependent Thalamo-Cortical Circuits Alteration in Schizophrenia

Schizophrenia is accompanied by aberrant interactions of intrinsic brain networks. However, the modulatory effect of electroencephalography (EEG) rhythms on the functional connectivity (FC) in schizophrenia remains unclear. This study aims to provide new insight into network communication in schizophrenia by integrating FC and EEG rhythm information. After collecting simultaneous resting-state EEG-functional magnetic resonance imaging data, the effect of rhythm modulations on FC was explored using what we term "dynamic rhythm information." We also investigated the synergistic relationships among three networks under rhythm modulation conditions, where this relationship presents the coupling between two brain networks with other networks as the center by the rhythm modulation. This study found FC between the thalamus and cortical network regions was rhythm-specific. Further, the effects of the thalamus on the default mode network (DMN) and salience network (SN) were less similar under alpha rhythm modulation in schizophrenia patients than in controls ([Formula: see text]). However, the similarity between the effects of the central executive network (CEN) on the DMN and SN under gamma modulation was greater ([Formula: see text]), and the degree of coupling was negatively correlated with the duration of disease ([Formula: see text], [Formula: see text]). Moreover, schizophrenia patients exhibited less coupling with the thalamus as the center and greater coupling with the CEN as the center. These results indicate that modulations in dynamic rhythms might contribute to the disordered functional interactions seen in schizophrenia.

Network hub centrality and working memory performance in schizophrenia

Cognitive impairment, and working memory deficits in particular, are debilitating, treatment-resistant aspects of schizophrenia. Dysfunction of brain network hubs, putatively related to altered neurodevelopment, is thought to underlie the cognitive symptoms associated with this illness. Here, we used weighted degree, a robust graph theory metric representing the number of weighted connections to a node, to quantify centrality in cortical hubs in 29 patients with schizophrenia and 29 age- and gender-matched healthy controls and identify the critical nodes that underlie working memory performance. In both patients and controls, elevated weighted degree in the default mode network (DMN) was generally associated with poorer performance (accuracy and reaction time). Higher degree in the ventral attention network (VAN) nodes in the right superior temporal cortex was associated with better performance (accuracy) in patients. Degree in several prefrontal and parietal areas was associated with cognitive performance only in patients. In regions that are critical for sustained attention, these correlations were primarily driven by between-network connectivity in patients. Moreover, a cross-validated prediction analysis showed that a linear model using a summary degree score can be used to predict an individual’s working memory accuracy (r = 0.35). Our results suggest that schizophrenia is associated with dysfunctional hubs in the cortical systems supporting internal and external cognition and highlight the importance of topological network analysis in the search of biomarkers for cognitive deficits in schizophrenia.

Aging: working memory capacity and spatial strategies in a virtual orientation task

Brain networks involved in working and spatial memory are closely intertwined, outlining a potential relation between these processes, which are also affected in non-pathological aging. Working memory is a pre-requisite for other complex cognitive processes. The main aim of this study is to explore how working memory capacity (WMC) can influence the asymmetrical decline in spatial orientation strategies in an older segment of population compared to young participants. Forty-eight older adults and twelve young students took part in the study. Working memory and spatial memory were assessed using the Change Localization Task and The Boxes Room Task, respectively. In The Boxes Room Task, two different configurations assessed the use of egocentric and allocentric reference frames. Results showed that older adults with better WMC outperformed those with lower WMC in several tasks. Independently of WMC capacity, older participants performed better in the allocentric condition of The Boxes Room. In addition, young participants outscored low WMC older participants, but did not differ from high WMC older adults. Overly, these findings support the important relationship between working memory capacity and spatial orientations abilities. Thus, basic cognitive mechanisms engaged in information processing could inform about other brain processes more complex in nature, like spatial orientation skills.