Periodic and Aperiodic Alterations of Resting‐State EEG in Schizophrenia Spectrum Disorders: Cognitive and Clinical Insights

Schizophrenia spectrum disorders (SSD) are marked by cognitive deficits and clinical symptoms linked to disrupted neural oscillations. While changes in spectral power are well documented in SSD, many studies have not clearly separated rhythmic (periodic) from the nonrhythmic (aperiodic) brain activity. This study examined both periodic and aperiodic resting‐state EEG components in SSD, recorded from 152 healthy controls and 97 SSD participants. EEG features (periodic power, bandwidth, center frequency; aperiodic exponent and offset) were extracted from global scalp averages and frontoinsular regions, including the dorsal anterior cingulate cortex (dACC), right anterior insula (R‐INS), and left anterior insula (L‐INS). At the scalp level, SSD individuals exhibited a global increase in theta power, along with a decreased alpha center frequency. Aperiodic activity showed increased exponent and offset in SSD. In frontoinsular regions, increased theta power was observed in the dACC, R‐INS, and L‐INS, along with lower alpha center frequency in L‐INS. No significant differences were found for aperiodic activity in these regions. Increased frontoinsular theta power, especially in the dACC, was associated with worse cognitive performance, particularly global cognition and working memory. These findings highlight the importance of separating periodic and aperiodic EEG activity in SSD, suggesting that periodic alterations, particularly in frontoinsular theta oscillations, may underlie cognitive dysfunction in SSD.