Caffeine Enhances Memory Performance in Young Adults during Their Non-optimal Time of Day

Abstract

Many college students struggle to perform well on exams in the early morning. Although students drink caffeinated beverages to feel more awake, it is unclear whether these actually improve performance. After consuming coffee (caffeinated or decaffeinated), college-age adults completed implicit and explicit memory tasks in the early morning and late afternoon (Experiment 1). During the morning, participants ingesting caffeine demonstrated a striking improvement in explicit memory, but not implicit memory. Caffeine did not alter memory performance in the afternoon. In Experiment 2, participants engaged in cardiovascular exercise in order to examine whether increases in physiological arousal similarly improved memory. Despite clear increases in physiological arousal, exercise did not improve memory performance compared to a stretching control condition. These results suggest that caffeine has a specific benefit for memory during students' non-optimal time of day - early morning. These findings have real-world implications for students taking morning exams.

Keywords: caffeine; cardiovascular exercise; explicit memory; implicit memory; time of day.

FIGURE 1

Change in perceived wakefulness across different points in Experiment 1 (A) and Experiment 2 (B). Perceived wakefulness ratings are presented as z-scores to compare across experiments with 95% confidence bands. After the data were transformed to z-scores, each participant’s baseline perceived wakefulness rating was subtracted from their rating at each time point to illustrate their change in wakefulness across the experiment.

FIGURE 2

Mean performance for cued recall and priming for Experiment 1 (A) and Experiment 2 (B). Cued recall was measured as the percentage of study words correctly recalled. Priming scores were calculated by subtracting normative baseline completion rates (Ryan et al., 2001) from the percentage of stems completed with the words from the study phase. Error bars show the 95% confidence intervals. ^∗p < 0.05.