Abstract:

Aerobic exercise is the rhythmic and continuous use of large muscle groups with sufficient oxygen supply. The aim of this review is to summarize previous research regarding the effects of aerobic exercise on working memory, episodic memory and implicit memory, and moderators among the relationships, such as timing of aerobic exercise, aerobic exercise duration, aerobic exercise intensity, cognitive engagement of aerobic exercise, age and gender. The following databases were used for the computerized searches: CNKI, Web of Science and PubMed. Aerobic exercise can improve processing speed in working memory tasks, denoted by both reaction time and event related potential. Moderate to vigorous intensity aerobic exercise before memory encoding or during consolidation can enhance episodic memory. Vigorous intensity aerobic exercise can promote implicit memory.
As for the moderators, a) timing of aerobic exercise has similar effects on the three types of memory. Aerobic exercise before memory encoding can promote all three types of memory (One study for working memory (Budde et al., 2010), one study for implicit memory (Angulo-Barroso et al., 2019), and for episodic memory in a previous meta-analysis, d = 0.11, 95% CI [-0.01, 0.23] (Loprinzi, Blough, et al., 2019)). Aerobic exercise during memory encoding can damage working memory (2 out of 3 studies have showed significant damaging effect (Loprinzi, 2018)) and episodic memory (d = -0.12, 95% CI [-0.22, -0.02] (Loprinzi, Blough, et al., 2019)), especially for vigorous intensity. Few studies have explored the effect of aerobic exercise during implicit memory encoding. Aerobic exercise during memory consolidation can promote episodic memory (d = 0.47, 95% CI [0.28, 0.67] (Loprinzi, Blough, et al., 2019)) and implicit memory (in one experimental study (Lundbye-Jensen et al., 2017)). b) Research synthesis indicates that chronic aerobic exercise is beneficial to working memory and episodic memory, while acute aerobic exercise has no significant effect. Yet, no study has directly compared the effects of acute and long-term aerobic exercise on implicit memory. c) Emerging research suggests that aerobic exercise intensity has different effect on the three kinds of memory. Moderate intensity aerobic exercise has positive effect on working memory. Vigorous intensity aerobic exercise can improve episodic memory and implicit memory. However, vigorous intensity aerobic exercise can negatively impacts working memory, which may lead to fatigue or interference, but this negative effect may be attenuated if the post-exercise recovery period is sufficient. d) Open skill aerobic exercise is performed in a dynamic and changing environment and require more cognitive engagement, such as football and basketball, while closed skill aerobic exercise take place in a predictable and static environment, requiring less cognitive engagement, such as rope skipping and stair climbing. The cognitive engagement of aerobic exercise may have positive effect on memory. e) The interactions are complex and several other moderators, such as types of memory (item memory and source memory), emotional characteristics of the learning materials, gender and age, should be carefully considered.
Next, we review the neurobiological mechanism underlying the effect of aerobic exercise on memory from the aspects of brain-derived neurotrophic factor (BDNF) and hippocampus. Animal studies generally show that BDNF is the mediator of the relationships between aerobic exercise and memory. However, the results of human research remain controversial. The change of BDNF lasts for only a few hours, thus it is easier to observe the increase of BDNF when sampling immediately after aerobic exercise. Specific gene affects the expression of BDNF. As for Val/Met heterozygous carriers, although aerobic exercise can negatively impact the episodic memory, studies have found that increasing aerobic exercise intensity can offset the adverse effects of Val/Met gene on working memory. Future research can focus on how aerobic exercise can improve the memory of Val/Met heterozygous carriers. Aerobic exercise can also cause long-term potentiation, activate hippocampus and other memory related brain areas, and induce neurogenesis. Future research can also test the laterality of fMRI activation to infer whether aerobic exercise can maintain the health of specific brain areas vulnerable to aging.
In conclusion, Future research should focus on the moderating effects of memory types, aerobic exercise timing and duration, aerobic exercise intensity and cognitive engagement, as well as age and gender, and explore the mediating role of BDNF and other molecular mechanisms (e.g., the endocannabinoid system) in human experiments, so as to reveal the neurobiological mechanism underlying the impact of aerobic exercise on memory.

Key words: aerobic exercise, memory, neurobiological mechanism