Alterations of oscillatory neuronal activity during reward processing in schizophrenia

Reward system dysfunctions are considered to be a pathophysiological mechanism in schizophrenia. Electrophysiological studies of reward system functions have identified frequency-specific brain networks for the processing of positive (high-beta frequency) and negative (theta frequency) events. Remarkably, midbrain dopaminergic signalling also includes theta and high-beta frequency modes, which have been assumed to reflect tonic and phasic dopamine responses, respectively. The aim of the present study was to identify alterations of oscillatory responses to reward feedback in patients with schizophrenia.

Seventeen patients with schizophrenia and 18 healthy controls performed a gambling task during recording of 64-channel electroencephalography. The theta and high-beta band total power were investigated in response to feedback events depending on feedback valence (loss or gain) and magnitude (5 vs. 25 points).

Both the increase of theta oscillatory activity in response to loss feedback (compared to gain feedback) and the increase of high-beta oscillatory activity in response to gain feedback (compared to loss feedback) were reduced in patients. The difference in high-beta responses to gain versus loss feedback in patients was associated with the severity of negative symptoms.

Our findings are consistent with current models of reward system dysfunction in schizophrenia, and indicate deficits in both cortical tonic and subcortical phasic dopamine activity, consistent with the complex dopaminergic abnormalities in schizophrenia.