Overnight Motor Memory Consolidation in Adolescents: Effects of Change in Dim Light Melatonin Onset After Sleep...

Adolescents experience chronic sleep restriction and developmental changes in circadian biology. Sleep aids adolescent learning and memory; the moderating effect of circadian rhythms is largely unknown. Here we examine adolescent sleep restriction, circadian biology, and memory consolidation. Adolescents were recruited for a larger experimental study. This study includes a subsample of individuals from the larger study who completed the motor sequence task (MST; added toward the end of data collection). Participants (M_AGE = 12.7, SD = 1.8; 62.5% male) completed a self-selected 9 h in bed sleep stabilization schedule for 19 nights followed by 7 nights of sleep restriction (6 h in bed; bedtime delayed and risetime advanced equally). In-lab dim light melatonin onset (DLMO) was assessed on the final nights of stabilization and restriction. The MST indexed overnight memory consolidation across the final night of sleep restriction. MST outcomes included the average number of correct sequences per trial, # of errors, and precision. We examined overnight improvement (morning-evening) in MST performance and associations between improvement, phase preference, DLMO_{Stabilization}, DLMO_Restriction, and DLMO_Shift (DLMO_{Stabilization} - DLMO_Restriction), controlling for age where statistically justified. The average number of correct sequences per MST trial improved, t(15) = -3.44, p < 0.01, d = 0.86, for the morning (12.94 ± 6.89) test session compared to evening (10.81 ± 5.69). There were no changes in errors or precision (ds < 0.14, ps > 0.34). Greater delays in DLMO phase (M ± SD: 10.34 ± 41.69 min) were associated with greater overnight improvement in the average number of correct sequences per trial, Adj. R² = 0.54, F(2, 13) = 9.79, p < 0.01, and errors, Adj. R² = 0.21, F(1, 15) = 4.94, p < 0.05. Overnight improvement was not related to phase preference (Adj. R²s < 0.17; ps > 0.05). These data highlight context dependent benefits of sleep for adolescent memory consolidation and indicate a potential link between circadian biology and the cognitive benefits of adolescent sleep. Understanding the influence of circadian rhythms in sleep-dependent memory may inform discussions of adolescent sleep loss and learning.