Disrupted rest-task shift of multi-band electroencephalography complexity in patients with schizophrenia

Brain activity undergoes intrinsic fluctuations with complexities specific to both the resting state and the task state. However, in patients with schizophrenia (SZ), where the boundary between internal and external realms is blurred, optimal modulation of these complexities between rest and stimulus phases is likely disrupted. Here, we present a frequency-dependent rest-task shift in electroencephalography (EEG) complexity in normal controls (NCs) and the associated abnormal patterns in patients with SZ. Specifically, we examined EEG complexity in different frequency bands, quantified by multiscale entropy (MSE), during the resting state and a 40 Hz auditory steady-state response (ASSR) task in 77 normal controls (NCs) and 103 patients with SZ. We compared the ASSR/resting MSE ratio between the NC and SZ groups. In the NC group, transitioning from the resting state to the ASSR state caused increased alpha-band entropy and decreased gamma-band entropy, whereas no such shifts were observed in patients with SZ. This study suggests that in NCs, alpha-band oscillatory complexity, which influences cortical response properties, increases during the transition from intrinsic to extrinsic information processing, while gamma-band oscillatory complexity decreases, likely due to concentration on auditory processing of a temporal enriching stimulation with high salience. Patients with SZ, which are marked by impaired neural synchrony, lacked the NCs' pronounced changes in neural complexity across frequency bands. This indicates that in patients with SZ, disruptions in the spontaneous activity that shapes the internal mental state may alter the properties of cortical responses and entrainment to external stimuli.