Neurobehavioral Impact of Successive Cycles of Sleep Restriction With and Without Naps in Adolescents

Abstract

Study objectives: To characterize adolescents' neurobehavioral changes during two cycles of restricted and recovery sleep and to examine the effectiveness of afternoon naps in ameliorating neurobehavioral deficits associated with multiple nights of sleep restriction.

Methods: Fifty-seven healthy adolescents (aged 15-19 years; 31 males) participated in a parallel group study. They underwent two cycles of sleep restriction (5-hr time in bed [TIB] for five and three nights in the first and the second cycles, respectively; 01:00-06:00) and recovery (9-hr TIB for two nights per cycle; 23:00-08:00) intended to simulate the weekday sleep loss and weekend attempt to "catch up" on sleep. Half of the participants received a 1-hr nap opportunity at 14:00 following each sleep-restricted night, while the other half stayed awake. Sustained attention, sleepiness, speed of processing, executive function, and mood were assessed 3 times each day.

Results: Participants who were not allowed to nap showed progressive decline in sustained attention that did not return to baseline after two nights of recovery sleep. Exposure to the second period of sleep restriction increased the rate of vigilance deterioration. Similar patterns were found for other neurobehavioral measures. Napping attenuated but did not eliminate performance decline. These findings contrasted with the stable performance of adolescents, given 9-hr TIB each night in our recent study.

Conclusions: Adolescents' neurobehavioral functions may not adapt to successive cycles of sleep curtailment and recovery. In sleep-restricted adolescents, weekend "catch-up sleep," even when combined with napping during weekdays, is inferior to receiving a 9-hr sleep opportunity each night.

Keywords: adolescents; neurobehavioral functions; recovery sleep; repeated cycles; sleep restriction; sustained attention.

Figure 1

Experimental protocol. (A) The 15-day experimental protocol is illustrated in a double raster plot. Both the nap and the no nap groups had two adaptation and baseline nights (B1 and B2; time-in-bed [TIB] = 9 hr), followed by the first cycle of sleep restriction for 5 nights (M₁1 to M₁5; TIB = 5 hr) and recovery sleep for 2 nights (R₁1 and R₁2; TIB = 9 hr). The second cycle consisted of 3 nights of sleep restriction (M₂1 to M₂3) and 2 nights of recovery sleep (R₂1 and R₂2). The nap group had a 1-hr nap opportunity between 14:00 and 15:00 on those days after a sleep restricted night (gray triangles), when the no nap group stayed awake (white triangles). Asterisks mark nocturnal sleep and daytime nap episodes monitored with polysomnography. A cognitive test battery (purple bars) was administered at 10:00, 15:45, and 20:00, except during the first and last days of the protocol. (B) Polysomnographically assessed total sleep time (TST) at night of the nap group (blue line and filled circles) and the no nap group (red line and filled circles) from baseline to the manipulation and recovery periods. The black dashed line represents the average TST of the control group from the Need for Sleep Study 1 when they were given a 9-hr sleep opportunity each night. TST during naps are indicated by blue open circles. (C) Sum of TST at night and during nap per 24-hr period. For (B) and (C), shaded areas represent the sleep restriction periods. The least square means and standard errors estimated with general linear mixed models are illustrated. ***p < .001; *p < .05 for contrasts between the no nap and the nap groups.

Figure 2

Performance in the psychomotor vigilance task (PVT). The number of PVT lapses of the control group (black line), the nap group (blue line), and the no nap group (red line) (A) averaged across the three test batteries each day, in the (B) morning, (C) afternoon, and (D) evening from the days after the last baseline night (day B2), the first cycle of sleep restriction nights with nap– wake manipulation (day M₁1 to M₁5) and recovery nights (R₁1 and R₁2), to the second cycle (day M₂1 to M₂3; and R₂1). Shaded areas represent the sleep restriction periods. The least square means and standard errors estimated with general linear mixed models are illustrated. ***p < .001; ** p < .01; *p < .05 for contrasts of the no nap or the nap group with the control group.