Sleep Spindle Abnormalities in Preschool Children With Autism Spectrum Disability: Insights From Nap Polysomnography

Sigma power and sleep spindles are key elements of Non-Rapid Eye Movement (NREM) sleep. They reflect anatomical and physiological properties of brain circuits, are linked with various behavioral outcomes in typically development (TD) children, and undergo significant modifications during development. Furthermore, recent studies have highlighted the potential of NREM sigma power and sleep spindles as early neurophysiological markers for autism spectrum disability (ASD). Here, we conducted polysomnography (PSG)/EEG recordings during afternoon naps on 50 children aged between 2 and 6 years, diagnosed with ASD or TD. EEG recordings from 19 scalp leads were analyzed, focusing on sigma power and sleep spindle parameters. EEG analyses revealed significant differences in power spectral density between ASD and TD children, particularly in the sigma band and adjacent alpha and beta bands, with increased power localized to anterior EEG leads in ASD children. Higher spindle amplitude and integrated spindle activity (ISA) were found in the ASD group, especially in frontal regions. Additional frequency-specific analyses (10-12 Hz, 12-14 Hz, 14-16 Hz) confirmed significant differences in spindle amplitude and distribution patterns, emphasizing the role of brain regions that are detectable from anterior EEG leads in ASD-related sleep abnormalities. No significant differences were found in spindle density, duration, or frequency outside specific clusters. These findings indicate that some sleep spindle parameters, particularly in frontal areas, are altered in ASD. The study highlights the feasibility of using afternoon nap PSG as a practical and effective method to detect these abnormalities in clinical settings. Future research should investigate the developmental trajectory of spindles in ASD and their potential role as neurophysiological biomarkers, offering valuable insights for diagnosis and prognosis.