Symptoms of anxiety are linked to N3 sleep and lower dissipation of slow-wave activity during nocturnal sleep

STUDY OBJECTIVES: Slow-wave sleep (SWS) is vital for brain health, memory, and emotional resilience. Slow-wave activity (SWA) reflects homeostatic sleep pressure, which dissipates across successive sleep cycles. Impaired SWA dissipation has been linked to depression. We examined whether reduced SWA dissipation is associated with symptoms of anxiety and depression in healthy conscripts. METHODS: Seventy conscripts (67 males, aged 18-24) undergoing compulsory military service participated in overnight polysomnography. SWA dissipation was assessed by comparing normalized delta (0.5-4.0 Hz) electroencephalogram power between first and third NREM sleep episodes. This was complemented by full spectral analysis of sleep stages. Psychological measures included Overall Anxiety Severity and Impairment Scale, Beck's Depression Inventory, and Epworth Sleepiness Scale. RESULTS: Conscripts with elevated anxiety (24%) exhibited weaker SWA dissipation and greater proportion of N3 sleep. Similarly, anxiety was negatively correlated with SWA dissipation and positively with proportion of N3. Additionally, conscripts with elevated anxiety but without elevated depressiveness had less REM sleep than those with both anxiety and depression, as well as those without symptoms. Findings related to sleepiness or depression without anxiety were limited. In full spectral analysis individuals with higher anxiety exhibited elevated alpha power during REM sleep, potentially reflecting cortical hyperarousal. CONCLUSIONS: Higher proportion of N3 sleep and lower SWA dissipation were associated with greater anxiety rather than depression. These findings highlight the importance of adequate SWS in emotion regulation. Impaired SWA dissipation may contribute to preservation of negative emotional memories during sleep. Another possibility is that hyperarousal increases need for recovery sleep.