Behavioral-induced Prefrontal Cortex Activation And Episodic Memory Function

Abstract

PURPOSE: Here we evaluated the effects of several behaviors (e.g., acute exercise, fist clenching, and saccades) on episodic memory, and whether prefrontal cortex oxygenation mediated these relationships. Six experiments were conducted to evaluate these direct and indirect effects. METHODS & RESULTS: Experiment 1 was a four-visit, within-subject, counterbalanced randomized controlled experiment. The visits included 1) exercise and saccadic eye movements, 2) exercise only, 3) saccadic eye movements only, and 4) no exercise and no saccadic eye movements (control). A word-list based episodic memory assessment was employed, including a long-term memory evaluation. The RM ANOVA was statistically significant (P=0.01, η2p=0.15), as the number of words recalled at the delay period were, respectively, 7.8 (2.7), 8.1 (2.7), 8.1 (2.3), and 6.6 (2.8). In our second experiment, we evaluated the effects of saccadic eye movements on prefrontal cortex oxygenation (PFC O2Hb), a proxy for neuronal activity. We found a main effect for time over a three-minute period, (P<0.001, η2p=0.31), representing higher oxygenation levels during saccadic eye movement. In our third experiment, we evaluated the effects of acute exercise on PFC O2Hb, which also demonstrated an increase in PFC O2Hb across time, (P=0.04, η2p=0.09). Experiment 4 replicated Experiment 1, but instead of saccadic eye movements, used a fist clenching protocol. The RM ANOVA was statistically significant (P<0.001, η2p=0.46), with memory being significantly better for the exercise only, fist only, and exercise + exercise visit compared to control. Experiment 5 evaluated the effects of fist clenching on PFC O2Hb. Results demonstrated a significant main effect for time, with oxygenation increasing during fist clenching, (P<0.001, η2p=0.35). Experiment 6 demonstrated that PFC oxygenation was statistically significantly positively associated with episodic memory function, in that, for every 1 μM increase in oxygenation during memory encoding, there was a 0.27 increase in the number of words (out of 8) recalled (b=0.27; 95% CI: 0.02, 0.52; p = .03). CONCLUSION These six experiments suggest that several behaviors may improve memory function and may, potentially, do so via increases in PFC O2Hb.