The infraslow fluctuation of sigma power during sleep in young individuals with schizophrenia

A well-replicated finding in schizophrenia is a reduction in sleep spindles, a major electrophysiological characteristic of Non-Rapid Eye Movement sleep. However, recent evidence indicates that even in healthy individuals, sleep spindles are not uniformly distributed throughout the night. Rather, they fluctuate rhythmically on an infraslow ∼50-second timescale, alternating between periods of high and low spindle activity. This fluctuation is referred to as the infraslow fluctuation of sigma power (10-16 Hz EEG activity, ISFS), which is modulated by noradrenergic activity from the locus coeruleus and seems to organize periods of arousability and periods of memory reactivation processes during sleep. Given the known deficit in sleep spindles, dysregulation of noradrenergic activity, and impairments in sleep maintenance and memory in schizophrenia, this study investigates the ISFS in sleep EEG data from individuals with either Childhood-Onset Schizophrenia (COS; N = 17) or Early-Onset Schizophrenia (EOS; N = 11), aged 9 to 21 years, alongside age- and sex-matched healthy controls (N = 56). The ISFS strength was reduced in both COS and EOS groups compared to controls, particularly in central-parietal electrodes. No significant difference in the ISFS strength was found between the two clinical groups, nor were there correlations between the ISFS strength and clinical characteristics or spindle density. These findings suggest that the ISFS is detectable but attenuated in young patients with schizophrenia, underscoring the value of considering spindle timing when probing disease mechanisms and designing interventions.