Afternoon nap and bright light exposure improve cognitive flexibility post lunch

PLoS One. 2015 May 27;10(5):e0125359. doi: 10.1371/journal.pone.0125359. eCollection 2015.


Beneficial effects of napping or bright light exposure on cognitive performance have been reported in participants exposed to sleep loss. Nonetheless, few studies investigated the effect of these potential countermeasures against the temporary drop in performance observed in mid-afternoon, and even less so on cognitive flexibility, a crucial component of executive functions. This study investigated the impact of either an afternoon nap or bright light exposure on post-prandial alterations in task switching performance in well-rested participants. Twenty-five healthy adults participated in two randomized experimental conditions, either wake versus nap (n=15), or bright light versus placebo (n=10). Participants were tested on a switching task three times (morning, post-lunch and late afternoon sessions). The interventions occurred prior to the post-lunch session. In the nap/wake condition, participants either stayed awake watching a 30-minute documentary or had the opportunity to take a nap for 30 minutes. In the bright light/placebo condition, participants watched a documentary under either bright blue light or dim orange light (placebo) for 30 minutes. The switch cost estimates cognitive flexibility and measures task-switching efficiency. Increased switch cost scores indicate higher difficulties to switch between tasks. In both control conditions (wake or placebo), accuracy switch-cost score increased post lunch. Both interventions (nap or bright light) elicited a decrease in accuracy switch-cost score post lunch, which was associated with diminished fatigue and decreased variability in vigilance. Additionally, there was a trend for a post-lunch benefit of bright light with a decreased latency switch-cost score. In the nap group, improvements in accuracy switch-cost score were associated with more NREM sleep stage N1. Thus, exposure to bright light during the post-lunch dip, a countermeasure easily applicable in daily life, results in similar beneficial effects as a short nap on performance in the cognitive flexibility domain with possible additional benefits on latency switch-cost scores.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Circadian Rhythm / physiology
  • Cognition / physiology*
  • Cognition / radiation effects
  • Fatigue / physiopathology
  • Female
  • Healthy Volunteers
  • Humans
  • Light*
  • Lunch*
  • Male
  • Sleep / physiology*
  • Wakefulness / physiology*
  • Wakefulness / radiation effects
  • Young Adult

Grants and funding

GD is a postdoctoral researcher supported by a "Greentic" grant from the «Département du développement technologique» (DGO6), Région Wallonne (Belgium). RS is a Postdoctoral Researcher at the Belgian Fonds National de la Recherche Scientifique (FNRS). RL is currently a recipient of a grant “Brains Back to Brussels” from the Brussels Institute for Research and Innovation (Belgium). Other than providing the luminotherapy device (Luminette), Lucimed was not involved in any part of the current study (finances, study design, data collection, data analysis, preparation of the manuscript).