Psychosocial Stress Before a Nap Increases Sleep Latency and Decreases Early Slow-Wave Activity

Abstract

Sleep disturbances are an important risk factor for stress-related diseases such as burnout or depression. In particular, slow-wave activity (SWA) during sleep might be eminently relevant for optimal maintenance of mental health and cognitive functioning. In spite of the clinical importance and the pertinence of stress-related processes in everyday life, the physiological mechanisms of the association between stress, sleep, and cognition are not well-understood. In the present study, we carefully mapped the time course of the influence of a psychosocial stressor on sleep architecture and sleep-related oscillations during a midday nap. We induced stress using a psychosocial laboratory stressor, the Montreal Imaging Stress Task, vs. a neutral control task. Afterward, participants were allowed to take a 90-min nap (n = 20) or stayed awake (n = 19) and cortisol was measured via saliva samples. We hypothesized that stress would decrease sleep efficiency and SWA in a time-dependent manner, with impairing effects on cognitive functioning. Psychosocial stress resulted in increased cortisol levels, which were elevated throughout the study interval. In the nap group, psychosocial stress increased sleep latency, but had only minor effects on sleep architecture. Still, SWA in the first 30 min of sleep was significantly reduced, whereas alpha activity was enhanced. These effects vanished after approximately 30 min. No impairing effect on cognitive functioning occurred. Our results show that psychosocial stress before sleep has an impact on sleep latency and early SWA during sleep. In contrast to our hypothesis, the effects were rather small and short-lasting. Importantly, cognitive functioning was maintained. We conclude that the effects of psychosocial stress before a nap are possibly better compensated than previously believed.

Keywords: cognition; cortisol; emotion; sleep; stress.

FIGURE 1

Displays the procedure of the experimental sessions and the main results on cortisol and sleep. (A) Procedure of the experiment. IAPS, picture memory task; SD, short delay; LD, long delay; PVT, psychomotor vigilance task. In (B) Baseline (sample 1) corrected cortisol values for wake and nap groups are reported for both conditions (stress in black versus control in white) separately. (C) Shows the overall effect of stress condition on sleep latency. (D) Shows effects in N1, (E) shows effects in N2 and (F) shows effects in N3 across the nap in 15 min segments. Asterisks indicate significant differences with p ≤ 0.05, trends are marked with +. The error bars represent standard errors of the marginal estimated means.

FIGURE 2

Displays how we defined the three regions frontal, central, parietal.

FIGURE 3

Effects of stress (black dots) versus control (white dots) on relative SWA (A–C) and alpha power (D–F) separately for frontal (A,D), central (B,E) and parietal (C,F) regions. Asterisks indicate significant stress effects in a within-subjects ANOVA with p ≤ 0.05. All indicated significant post hoc comparisons survived the correction for multiple comparisons using the Fisher–Hayter Procedure. The error bars represent standard errors of the marginal estimated means.