EC Neurology

The non-rapid eye movement (NREM) sleep is considered a true resting state for the brain, yet the physiologic drivers of neural activity in this phase remain undetermined. Neural activity may be endogenously driven to compensate for minimal sensory stimulation, or by physiologic processes associated with development, or the autonomic tone. To address this issue, we examined brain activity and autonomic tone during stage 2, NREM sleep over a cohort of 93 subjects, from toddlers to young adults. Brain activity was quantified as total counts of EEG spindles and spontaneous K-complexes over 30 minutes of uninterrupted sleep. Autonomic tone during sleep was measured as baseline heart rate and amplitude of respiratory sinus arrhythmia

Blood pressure was also measured at rest. On average, spindle and K-complex counts increased by 8 and 1 units, respectively, with each additional year of development. Furthermore, spindle and K-complex densities were strongly correlated even after adjusting for age, which suggests a common underlying mechanism. Across subjects, spindles were on average 15 times more abundant than spontaneous K-complexes. Gender did not significantly influence any of these trends. Regarding autonomic tone, spindles and K-complex densities were anticorrelated with baseline heart rate and positively correlated with blood pressure, but these correlations are explained by natural covariations with age. Finally, neither respiratory rate nor sinus arrhythmia correlated with spindle or K-complex density, after adjusting for age. These results collectively demonstrate that spindle and spontaneous K-complex densities increase progressively with age during development into adulthood and are unrelated to baseline autonomic tone

 Keywords: Non-REM Sleep; Heart Rate Variability; Children; Development

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