Sleep disturbances are a common feature of psychotic disorders, and subjective sleep disturbances have been consistently reported in individuals at clinical high-risk for psychosis (CHR) (Lederman et al., 2017; Lunsford-Avery et al., 2015; Zaks et al., 2022; Zanini et al., 2015). Previous studies have investigated sleep architecture in this population (Lunsford-Avery et al., 2015; Mayeli et al., 2021; Purple et al., 2020; Zanini et al., 2015), revealing lower sleep efficiency (Lunsford-Avery et al., 2015) and higher sleep latency (Zanini et al., 2015) and wakefulness after sleep onset (Mayeli et al., 2021; Zanini et al., 2015) in CHR compared to healthy control (HC) subjects. However, as highlighted by a recent meta-analysis from our group, a gap remains in the literature regarding specific investigations of slow wave abnormalities and spindle characteristics in at-risk individuals (Bagautdinova et al., 2023). In a recently published study, we examined sleep spindle features in CHR compared to HC subjects (Mayeli et al., 2022c) and established reduced spindle duration in CHR individuals in centro-parietal and prefrontal regions, indicating alterations in sleep neurophysiology within this population. Of note, spindle deficits have been reported in chronic, early course, and first-episode psychosis (FEP) patients, thus suggesting that they may represent a trait neurophysiological biomarker for psychotic disorders (Lüthi, 2014).

Beside sleep spindles, slow waves are the other main oscillatory brain activity occurring during non-rapid eye movement (NREM) sleep, and contribute to various neural processes (Dijk, 2009). Slow waves are characterized by ∼1 Hz EEG oscillations and reflect the synchronized interactions between cortical neurons, manifesting as alternating up and down states of neuronal depolarization and hyperpolarization respectively (Adamantidis et al., 2019). Our group has recently shown a reduction in slow wave density during sleep in FEP patients in frontal-prefrontal regions, and this reduction was associated with the severity of the positive symptoms experienced by these individuals (Kaskie et al., 2019). Intriguingly, slow wave density does not appear to differ significantly in individuals with chronic schizophrenia (Ferrarelli et al., 2010; Kozhemiako et al., 2022), suggesting that this sleep abnormality may be particularly relevant in the early stages of psychosis and could serve as a potential state biomarker for these disorders.

In this study, our primary objective was to examine the presence of slow wave abnormalities during sleep in CHR individuals. We employed high-density electroencephalography (hd-EEG) recordings to comprehensively investigate various parameters related to slow wave activity, including activity, density, and amplitude. Additionally, we aimed at investigating the relationship between slow wave abnormalities and subthreshold psychotic experiences in CHR subjects.