Background: The study of the cortical functional network properties in schizophrenia (SZ) may benefit from the
use of graph theory parameters applied to high-density electroencephalography (EEG). Connectivity Strength
(CS) assesses global synchrony of the network, and Shannon Graph Complexity (SGC) summarizes the network
distribution of link weights and allows distinguishing between primary and secondary pathways. Their joint use
may help in understanding the underpinnings of the functional network hyperactivation and task-related
hypomodulation previously described in psychoses.
Methods: We used 64-sensor EEG recordings during a P300 oddball task in 128 SZ patients (96 chronic, CR, and
32 first episodes, FE), as well as 46 bipolar disorder (BD) patients, and 92 healthy controls (HC). Pre-stimulus and
modulation (task-response minus pre-stimulus windows values) of CS and SGC were assessed in the theta band
(4–8 Hz) and the broadband (4–70 Hz).
Results: Compared to HC, SZ patients (CR and FE) showed significantly higher pre-stimulus CS values in the
broadband, and both SZ and BD patients showed lower theta-band CS modulation. SGC modulation values, both
theta-band and broadband, were also abnormally reduced in CR patients. Statistically significant relationships
were found in the theta band between SGC modulation and both CS pre-stimulus and modulation values in
patients. CS altered measures in patients were additionally related to their cognitive outcome and negative
symptoms. A primary role of antipsychotics in these results was ruled out.
Conclusions: Our results linking SGC and CS alterations in psychotic patients supported a hyperactive and
hypomodulatory network mainly involving connections in secondary pathways.
