Physical exercise has been shown to enhance memory and to increase neuroplasticity. Rodent studies have revealed modulating effects of signaling molecules of the immune system (cytokines) on hippocampal plasticity and memory. Acute and chronic exercise have been both found to alter the number and function of immune cells. Thus, physical exercise might enhance neuroplasticity via an altered immune response. In this study we tested whether multiple repetitions of a vocabulary learning task combined with a bout of cardiovascular exercise enhances learning in humans and whether memory improvements correlated with acute exercise-induced cytokine changes. Data of 52 participants (20-40 years of age) who were randomly assigned to a cardiovascular exercise group (cycling) or a control group (stretching) were analyzed. During the 10-week treatment, participants completed 18 learning-exercise sessions. In each of these sessions, the vocabulary learning task was always performed immediately before exercising started. To assess acute exercise-induced changes in cytokine levels, blood sampling was performed at rest and immediately after exercising in two of the sessions. Learning success measured as increase in learning across all sessions and vocabulary retention four weeks after the treatment had ended did not differ between groups. The cycling group showed a relatively larger acute increase in IL-6, IL-1ra, IL-4, and IFN-γ compared to the stretching group. Exploratory analyses revealed significant positive associations between within-session learning and acute exercise-induced increases in IL-6 and IL-1ra in the cycling group only. These results suggest that the immune system may act as a mediator of exercise-induced cognitive benefits.
Keywords: Cytokines; Immunology; Learning; Memory; Physical exercise.
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