COMBINED EXERCISE AND COGNITIVE TRAINING ENHANCES HIPPOCAMPAL-DEPENDENT MEMORY

Abstract

There is an established link between exercise, neurogenesis, and memory. Most of this research has been focused on rodent models, with little known about the effects of exercise on cognition in young adults. In rodents, exercise promotes hippocampal neurogenesis by enhancing cell proliferation in the dentate gyrus, while cognitive training promotes hippocampal neurogenesis by enhancing cell survival. Both physical exercise and cognitive training independently induce hippocampal neurogenesis in rodents, suggesting that these different forms of training may work through complimentary neurological pathways to benefit hippocampal memory in young adults. The present study examined the effects of six weeks of physical exercise and cognitive training on hippocampal-mediated memory processes in young adults to determine whether combined training yields enhanced memory benefits. Sixty-six sedentary young adults (32 females; age range 17-30 years) were randomly assigned to one of four groups: 1) Exercise training group (n=15), 2) Cognitive training group (n=16), 3) Combined exercise and cognitive training group (n=18), or 4) No-contact control group (n=17). Memory performance was assessed before and after the intervention on a putative hippocampal neurogenesis-dependent task, the Pattern Separation task. Growth factors that support neuron survival and function, brain-derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1) were measured in blood serum using enzyme-linked immunosorbent assays (ELISA). Based on the literature, the combination of exercise and cognitive training was expected to improve pattern separation performance more than the exercise or cognitive training alone, and display augmented effects for high responders to the exercise training. Additionally, if BDNF and IGF-1 were found to be involved in the mechanisms regulating the observed changes in memory, they too were expected to increase the most from the combined training and be dependent on individual changes in aerobic fitness. Critically, the combination of exercise and cognitive training led to the greatest increase in memory requiring pattern separation [t(16) = 2.91, p < 0.01] , indicating improved hippocampal-mediated memory function. BDNF and IGF-1 were not associated with this change in memory performance but were associated with the individual’s response to the exercise training, such that high responders to exercise had greater BDNF [F(1, 29) = 7.81, p < 0.01] and IGF-1 [F(1, 29) = 5.09, p < 0.05] than low responders to exercise. The results suggest that exercise and cognitive training may work through synergistic mechanisms to enhance hippocampal neurogenesis and support pattern separation processing. However, BDNF and IGF-1 may not be mediating this change in memory function.