Comparison of sleep spindles’ characteristics in descending compared to ascending slope of the NREM/REM sleep cycle

Sleep microstructural elements’ distribution and features differ between descending (D) and ascending (A) NREM slopes of each sleep cycle, reflecting the asymmetrical dynamics of sleep- and wake-promoting neuronal systems [1]. Among these elements, sleep spindles and K-complexes play significant roles in sleep regulation and sensory processing during sleep. This study aims to compare the distribution of sleep spindles and spontaneous K-complexes (KC) in D and A NREM sleep. All-night polysomnographic recordings of young, healthy sleepers were examined and sleep cycles with a regular, uninterrupted by prolonged wakefulness, succession of sleep stages were selected for quantitative analysis. Calculated parameters for D and A slopes of each sleep cycle include their duration, the rate of appearance of sleep spindles and KC, as well as the mean duration and inter-event interval distribution of sleep spindles. Our results indicate that D NREM slopes of sleep cycles are of longer duration and lower composition in KC than A slopes, confirming previous reports concerning their respective domination by sleep- and wake-promoting mechanisms [1]. Moreover, we found that sleep spindles in D appear more frequently, although have comparable 0.2-0.3 Hz periodicity and mean duration to those in A NREM sleep. We view the above results as providing support to the hypothesis of sensory input-driven NREM sleep regulation [1] Comparison of sleep spindles’ characteristics in descending compared to ascending slope of the nrem/rem sleep cycle (PDF Download Available)