Abnormal spontaneous activity and rest–task shift in schizophrenia

Aims: 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. Methods: 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. Results: 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). Conclusion: 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.