Abstract and Introduction
We examine the novel hypothesis that physical exercise and sleep have synergistic effects on memory. Exercise can trigger mechanisms that can create an optimal brain state during sleep to facilitate memory processing. The possibility that exercise could counteract the deleterious effects of sleep deprivation on memory by protecting neuroplasticity also is discussed.
Physical exercise and sleep are two seemingly opposing activities, which have shown, separately, to have positive effects on different types of memory. Most research studying the effects of exercise on memory has focused on cardiovascular exercise. Performing exercises such as running or cycling improves our capacity to store information about facts and events (i.e., declarative memory) as well as motor skills (i.e., procedural memory). Similarly, sleep plays an important role in consolidating the declarative and procedural information that we encode during the day, making it less susceptible to interference, and storing it as long-term memory. Given the different nature of physical exercise and sleep, one might assume that the enhancing effects that these two activities have on memory are irremediably mediated through different pathways. However, emerging evidence suggests that exercise and sleep can work synergistically to improve memory.
The mechanistic underpinnings through which physical exercise and sleep can synergize to impact memory are, however, not well understood. As distinct brain pathways can be engaged during the neural processes that dictate the fate of a memory during wakefulness and sleep, one could argue that the mechanisms by which exercise and sleep improve memory also operate independently. However, mounting evidence indicates that physical exercise triggers a vast array of physiological processes that modify key aspects of sleep, which have an important role in memory processing.[5,6] Hence, it is not inconceivable that the positive effects that exercise has shown to have on different types of memory could be mediated, at least in part, by exercise-induced changes in sleep. Studying the mechanistic interplay between physical exercise and sleep could provide important information to design more effective exercise interventions aimed at maintaining or improving the memory function of sleep.
Lack of sleep reduces work productivity, increases traffic- and work-related accidents, medical errors, and the risk of cognitive impairment. Even short periods of sleep deprivation result in maladaptive changes in neuroplasticity, which can impair memory processing. Because some of the deleterious effects that sleep loss has on neuroplasticity are diametrically opposed to the positive effects of physical exercise,[9–14] it is not inconceivable that, by preserving neuroplasticity, exercise could protect memories against the effects of sleep loss. However, there is still little information regarding how exercise-induced changes in neuroplasticity can impact memory processing in the sleep-deprived human brain. Given the alarming amounts of sleep insufficiency worldwide, its immense societal and economic costs, and the strong link between sleep insufficiency and memory deterioration, studying interactions between physical exercise, sleep loss, and memory is important.
This brief review examines the hypothesis that physical exercise and sleep can have synergistic effects on memory. We start by providing a basic overview of the mechanisms of sleep involved in memory processing and how exercise modifies them. We will then review emerging evidence supporting the synergistic effect that exercise and sleep can have on declarative and procedural memory. We focus mainly on acute studies using a single bout of exercise performed either before or after memory encoding because this exercise paradigm is ideally suited to study time-locked mechanistic interactions between exercise and sleep and their combined effects on memory. We also discuss potential pathways that could bridge the effects of these two activities on memory, analyzing studies that demonstrate that exercise triggers processes that influence sleep mechanisms modulating memory. Finally, we discuss whether exercise can protect memory from the deleterious effects of sleep deprivation and the potential role of neuroplasticity in mediating such a protective effect.
Exerc Sport Sci Rev. 2022;50(1):38-48. © 2022 American College of Sports Medicine