Abstract
The present study evaluated brain connectivity using electroencephalography (EEG) data from 14 patients with schizophrenia and 14 healthy controls. Phase-Locking Value (PLV), Phase-Lag Index (PLI) and Directed Transfer Function (DTF) were calculated for the original EEG data and following current source density (CSD) transformation, re-referencing using the average reference electrode (AVERAGE) and reference electrode standardization techniques (REST). The statistical analysis of adjacency matrices was carried out using indices based on graph theory. Both CSD and REST reduced the influence of volume conducted currents. The largest group differences in connectivity were observed for the alpha band. Schizophrenic patients showed reduced connectivity strength, as well as a lower clustering coefficient and shorter characteristic path length for both measures of phase synchronization following CSD transformation or REST re-referencing. Reduced synchronization was accompanied by increased directional flow from the occipital region for the alpha band. Following the REST re-referencing, the sources of alpha activity were located at parietal rather than occipital derivations. The results of PLV and DTF demonstrated group differences in fronto-posterior asymmetry following CSD transformation, while for PLI the differences were significant only using REST. The only analysis that identified group differences in inter-hemispheric asymmetry was DTF calculated for REST. Our results suggest that a comparison of different connectivity measures using graph-based indices for each frequency band, separately, may be a useful tool in the study of disconnectivity disorders such as schizophrenia.
Highlights
Schizophrenia is considered as a disorder of brain disconnectivity [1,2], characterized by profound disruption of large-scale prefronto-temporal interactions [3]
The influence of reference electrode on volume conduction effects Comparison of the results obtained based on the original EEG data with those following current source density (CSD) transformation and reference electrode standardization techniques (REST) re-referencing revealed a reduced impact from common sources
Our results demonstrate that decreased synchronization is accompanied by increased information flow, quantified by Directed Transfer Function (DTF) strength connectivity following CSD transformation
Summary
Schizophrenia is considered as a disorder of brain disconnectivity [1,2], characterized by profound disruption of large-scale prefronto-temporal interactions [3]. Magnetic resonance imaging (MRI) studies in patients with schizophrenia have revealed gray matter volume deficits in the medial temporal lobe (including hippocampus) and in the heteromodal association cortex (including the prefrontal, anterior cingulate, superior temporal and parietal cortex, and the thalamus), as well as enlargement of the ventricles [4]. Graph-based analysis of brain connectivity in schizophrenia prefrontal and temporal cortex, and reductions in the myelin membranes [5]. The limbic pathways connecting the hippocampus with the prefrontal cortex, anterior cingulate cortex, and thalamus are involved in higher cognition and information processing [6]. One consequence of abnormal connectivity in schizophrenia may be a loss of coherent functional integration that results in a disorder of association processes
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