Abstract
At present, little is known about brain functional connectivity and its small-world topologic properties in first-episode schizophrenia (SZ) patients during cool executive function task. In this paper, the Trail Making Test-B (TMT-B) task was used to evaluate the cool executive function of first-episode SZ patients and electroencephalography (EEG) data were recorded from 14 first-episode SZ patients and 14 healthy controls during this cool executive function task. Brain functional connectivity between all pairs of EEG channels was constructed based on mutual information (MI) analysis. The constructed brain functional networks were filtered by three thresholding schemes: absolute threshold, mean degree, and a novel data-driven scheme based on orthogonal minimal spanning trees (OMST), and graph theory was then used to study the topographical characteristics of the filtered brain graphs. Results indicated that the graph theoretical measures of the theta band showed obvious difference between SZ patients and healthy controls. In the theta band, the characteristic path length was significantly longer and the cluster coefficient was significantly smaller in the SZ patients for a wide range of absolute threshold T. However, the cluster coefficient showed no significant changes, and the characteristic path length was still significantly longer in SZ patients when calculated as a function of mean degree K. Interestingly, we also found that only the characteristic path length was significantly longer in SZ patients compared with healthy controls after using the OMST scheme. Pearson correlation analysis showed that the characteristic path length was positively correlated with executive time of TMT-B for the combined SZ patients and healthy controls (r = 0.507, P = 0.006), but not for SZ patients alone (r = 0.072, P = 0.612). The above results suggested a less optimal organization of the brain network and could be useful for understanding the pathophysiologic mechanisms underlying cool executive dysfunction in first-episode SZ patients.
Highlights
Schizophrenia (SZ), one of the most serious mental disorders, usually causes many aspects of cognitive dysfunction, including memory, attention, and executive function [1]
We observed that changes of small-world network properties mainly appeared in the theta band, not in the delta, alpha, or beta band, and the SZ group was characterized by a longer characteristic path length L and relatively higher cluster coefficient C in the theta band, suggesting a less optimal organization of the brain network in SZ patients
Previous literatures have reported that SZ patients need to spend more time to finish some executive tasks due to their executive dysfunction [3, 45], and our results indicated that the mean executive time of Trail Making Test-B (TMT-B) task for SZ patients was significantly longer than that of healthy controls, which was consistent with these literatures
Summary
Schizophrenia (SZ), one of the most serious mental disorders, usually causes many aspects of cognitive dysfunction, including memory, attention, and executive function [1]. A large number of studies have shown that patients with schizophrenia are accompanied by severe executive dysfunction [5,6,7,8]. A large number of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) studies have confirmed dysfunctional connectivity in SZ patients [10,11,12,13,14,15,16]. Among the usually applied methods to study functional connectivity, such as coherence and correlation coefficient, mutual information (MI) has been widely applied in many studies to investigate the information communication and connectivity among different brain regions [11, 17, 18]. Some researchers tried to use MI to study schizophrenia, but the results do not seem consistent [11, 17, 20]
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