Abnormal spontaneous activity and rest-task shift in schizophrenia.

Schizophrenia (SZ) is associated with abnormalities in both spontaneous and task-evoked neural oscillations, and growing evidence shows that shift patterns of oscillatory activity between resting and task states are also disturbed. However, no study has simultaneously examined the frequency- and state-specific characteristics of oscillatory deficits in SZ. Using an auditory steady-state response (ASSR) paradigm, we aimed to examine the differential sensitivity of oscillatory measures to SZ and to assess rest-task shifts across multiple frequency bands. We recorded resting-state activity and 40 Hz ASSR of 66 neurotypical controls (NC) and 68 SZ patients using electroencephalography (EEG). 40 Hz stimulus-evoked activity was measured using evoked power, phase-locking factor (PLF), and phase-locking angle, whereas multi-frequency (4-100 Hz) spontaneous activity during ASSR and resting states was assessed using induced and resting power. The state-dependent shifts in spontaneous activity between the resting and ASSR states were evaluated over a broad frequency range. Both induced and resting power in the low-frequency range (4-10 Hz) were elevated over widespread regions in SZ patients relative to NC. Gamma-band (39-100 Hz) induced power then demonstrated excellent ability to discriminate between SZ and NC. In addition, SZ patients showed a reduced rest-task shift in the theta-beta band (5-23 Hz) spontaneous power, most pronounced in the alpha-band (8-13 Hz). The present study confirmed the utility of gamma-band induced power during ASSR stimulation for differentiating SZ patients from NC. Importantly, our results also highlight the pathophysiological significance of the reduced rest-task shift pattern of spontaneous activity mainly in the alpha-band in SZ patients.