The Effects of Caffeine and Exercise on Implicit and Explicit Memory Performance in Younger Adults: an Investigation of Physiological Arousal

Abstract

Memory performance is best during an individual’s optimal time-of-day, when physiological arousal is naturally highest, and decreases significantly during their non-optimal time of day when arousal declines. Previous research suggests that the time-of-day at which a memory task is completed may contribute to age related disparities in memory performance. Ryan et al. (2002) found that this deficit could be eliminated in older adults by administering caffeine during their non-optimal time-of-day, the late afternoon. However, there are no benefits of caffeine if administered during an individual’s optimal time of day. It remains unclear whether the same patterns of effects of caffeine would be seen in younger adults. Experiment 1 examined whether caffeine enhanced memory in the early morning. Thirty minutes after consuming a cup of coffee (caffeinated or decaffeinated), participants completed implicit and explicit versions of a word stem completion task. Young adults who consumed caffeinated coffee demonstrated significant improvements in explicit memory, but not implicit memory. Experiment 2 examined the effect of caffeine in younger adults during their optimal time of day, where results show that caffeine had no effect on memory performance. This suggests that that caffeine serves a compensatory role, aiding time-of-day deficits. Finally, experiment 3 examined whether exercise would also ameliorate time-of-day deficits. Young adults completed 15 minutes of either cardiovascular exercise or gentle stretching. Heart rates were taken throughout the experiment to measure physiological arousal. While exercise clearly increased physiological arousal, exercise had no effect on either explicit or implicit memory. Taken together, these results suggest a unique mechanism for caffeine-induced arousal that compensates for time-of-day memory deficits.