A 20-minute exercise bout and 90-minute nap produced similar episodic memory performance following 30 hours of wakefulness but engaged distinct neural mechanisms.
A brief bout of aerobic exercise and a 90-minute nap each may help preserve episodic memory encoding following prolonged sleep deprivation compared with no intervention, although the 2 strategies appeared to support memory through different neural mechanisms.
The randomized laboratory study enrolled 54 healthy participants aged 18 to 35 years with no history of neurologic, psychiatric, or sleep disorders and no night-shift work. Following 30 hours of continuous wakefulness, participants were randomly assigned to 20 minutes of moderate- to vigorous-intensity aerobic exercise at 80% of maximum heart rate, a 90-minute nap opportunity, or a 20-minute control period spent sitting on a stationary bicycle without pedaling. Participants then viewed 150 images during an encoding session with 64-channel electroencephalography (EEG), followed by a surprise recognition test 3 days later. Behavioral analyses included 18 participants in each intervention group and 17 controls.
The primary memory outcome was hit rate, or the proportion of previously presented images correctly recognized at testing. Researchers also assessed false-alarm rate, discrimination ability, response bias, fatigue, and EEG markers related to sleep pressure, neural fatigue, and memory encoding. EEG analyses included 15 participants in each intervention group and 13 controls.
Hit rates were 21% higher following exercise and 23% higher following napping compared with control, with large effect sizes (Cohen d = 1.0 and 0.91, respectively). Mean hit rates were 0.56 in the exercise group, 0.57 in the nap group, and 0.46 in the control group. Memory performance did not significantly differ between the exercise and nap groups.
The interventions differed in their effects on fatigue. Participants who napped reported less postintervention fatigue than those in the exercise and control groups, whereas fatigue did not significantly differ between the exercise and control groups. Despite similar fatigue levels in the latter 2 groups, participants who exercised had better memory performance than controls. Response bias did not significantly differ among the groups.
EEG findings suggested that exercise and napping supported memory through distinct neural contributions. Both interventions were associated with lower delta activity related to neural fatigue in task-relevant brain regions compared with control, with the lowest activity observed following napping. Napping was also associated with lower frontal slow-wave activity, a marker of sleep pressure, compared with control, whereas exercise and control did not significantly differ on this measure.
Within the exercise group, P300 amplitude and beta event-related desynchronization during correctly remembered trials emerged as the strongest neural predictors of hit rate. In the nap group, prestimulus theta activity and slow-wave event-related synchronization emerged as the strongest predictors. None of these neural markers significantly predicted memory performance in the control group. The researchers suggested that exercise facilitated efficient neural processing during memory encoding, whereas napping produced a brain state more conducive to new learning.
However, the behavioral benefit was not observed across all recognition-memory measures. False-alarm rates and discrimination index scores did not significantly differ among the groups. Researchers noted that the 3-day interval between encoding and testing was intended to allow recovery from sleep deprivation and minimize residual intervention effects on retrieval, which may have contributed to the absence of differences in false-alarm rates.
The study had several limitations. Laboratory-induced acute sleep deprivation may not reflect chronic sleep insufficiency commonly experienced in real-world or shift-work settings. Investigators did not assess education, socioeconomic status, or occupation and did not perform source localization for EEG oscillations. The study also lacked a separate nap-control group, and the exercise and nap interventions differed in duration. The researchers noted that matching the intervention durations could have resulted in an insufficient sleep stimulus or excessive exercise-related fatigue.
The findings suggest that brief aerobic exercise may offer a strategy for preserving episodic memory encoding following acute sleep deprivation when napping is impractical, but the researchers emphasized that the results require validation in real-world settings and should not be interpreted as evidence that exercise can replace sleep.
“It should be made clear, however, that while exciting, these results do not represent an endorsement of the idea that exercise can replace the many functions of sleep,” wrote lead study author Madhura S. Lotlikar, of the Department of Neurology and Neurosurgery at McGill University, and colleagues.
The authors reported no competing interests.
