Is gamma band EEG synchronization reduced during auditory driving in schizophrenia patients with auditory verbal hallucinations?

Auditory verbal hallucinations (AVH) in schizophrenia patients assumingly result from a state inadequate activation of the primary auditory system. We tested brain responsiveness to auditory stimulation in healthy controls (n = 26), and in schizophrenia patients that frequently (n = 18) or never (n = 11) experienced AVH. Responsiveness was assessed by driving the EEG with click-tones at 20, 30 and 40 Hz. We compared stimulus induced EEG changes between groups using spectral amplitude maps and a global measure of phase-locking (GFS). As expected, the 40 Hz stimulation elicited the strongest changes. However, while controls and non-hallucinators increased 40 Hz EEG activity during stimulation, a left-lateralized decrease was observed in the hallucinators. These differences were significant (p = .02). As expected, GFS increased during stimulation in controls (p = .08) and non-hallucinating patients (p = .06), which was significant when combining the two groups (p = .01). In contrast, GFS decreased with stimulation in hallucinating patients (p = 0.13), resulting in a significantly different GFS response when comparing subjects with and without AVH (p < .01). Our data suggests that normally, 40 Hz stimulation leads to the activation of a synchronized network representing the sensory input, but in hallucinating patients, the same stimulation partly disrupts ongoing activity in this network.