Effects of acute exercise on memory: Considerations of exercise intensity, post-exercise recovery period and aerobic endurance.

Accumulating research demonstrates that acute exercise can enhance long-term episodic memory. However, it is unclear if there is an intensity-specific effect of acute exercise on long-term episodic memory function and whether this is influenced by the post-exercise recovery period, which was the primary objective of this experiment. Another uncertainty in the literature is whether aerobic endurance influences the interaction between exercise intensity and post-exercise recovery period on long-term episodic memory function, which was a secondary objective of this study. With exercise intensity and post-exercise recovery period occurring as within-subject factors, and fitness as a between-subject factor, 59 participants (Mage = 20 years) completed 12 primary laboratory visits. These visits included a 20-min bout of exercise (Control, Moderate, and Vigorous), followed by a recovery period (1, 5, 10, and 15 min) and then a word-list episodic memory task, involving an encoding phase and two long-term recall assessments (20-min and 24-h delayed recall). The primary finding from this experiment was that moderate and vigorous-intensity exercise improved memory function when compared to a non-exercise control. A secondary finding was that individuals with higher levels of aerobic endurance, compared to their lesser fit counterparts, had greater memory performance after exercise (moderate or vigorous) when compared to after a control condition. Additionally, individuals with higher levels of aerobic endurance, compared to their lesser fit counterparts, generally performed better on the memory task with longer post-exercise recovery periods. Future research should carefully consider these parameters when evaluating the effects of acute exercise on long-term episodic memory.

Vigorous-intensity acute exercise during encoding can reduce levels of episodic and false memory.

The potential benefits (veridical memory) and, importantly, costs (false memory) of acute exercise on memory in conjunction with the timing and type of exercise have not been fully studied. In Experiment 1, we employed a three-condition (15-minute vigorous-intensity acute exercise Before or During memory encoding, or a Control condition of watching a video), within-subjects, counterbalanced design. The procedures included an immediate and delayed (20-minute post encoding) free recall assessment. Veridical memory was determined by the number of studied words that were recalled, whereas false memory was determined by retrieving a non-presented, critical item. For veridical memory, Before was not different than Control (p = .42), however, During was worse than Before and Control (p's < .001). No differences occurred for false memory. Experiment 2 was conducted that included several additional exercise conditions (e.g., light-intensity exercise) during memory encoding, used a recognition task instead of a free recall task, and extended the long-term memory assessment out to 24-hours. Experiment 2 demonstrated that vigorous-intensity acute exercise during encoding reduced both veridical and false memory for related new items (p < .05). These findings demonstrate that the timing and intensity of exercise play an important role in influencing memory performance.

Effects of acute exercise intensity on source episodic memory and metamemory accuracy.

Prior research suggests that behavioural (e.g., exercise) and psychological factors (e.g., metamemory; monitoring and control of one's memory processes) may influence memory function. However, there is conflicting results on the optimal intensity of acute exercise to enhance memory and whether acute exercise can also enhance metamemory. Furthermore, very limited research has evaluated whether acute exercise can influence source episodic memory. The objective of this study was to evaluate whether there is an intensity-specific effect of acute exercise on source episodic memory and metamemory accuracy. Thirty young adults participated in a three-condition (control/moderate/vigorous-intensity exercise), within-subject counterbalanced experimental study. After each intervention, participants completed source episodic memory and metamemory tasks. Results demonstrated that acute exercise, relative to control, was effective in enhancing source episodic memory, but not metamemory accuracy. Vigorous-intensity acute exercise was the most optimal intensity to enhance source episodic memory. Overall, our findings suggest that there is an intensity-specific effect of acute exercise on source episodic memory. Furthermore, when exercise-related improvements in memory occur, young adults may be unaware of these memory benefits from exercise.

Acute aerobic exercise improves memory across intensity and fitness levels.

The present study was designed to examine the impact of exercise intensity and aerobic fitness on free recall, judgments of learning (JOLs), and metacognitive accuracy. In Experiment 1, 30 college students engaged in either (1) no exercise, (2) light exercise (55% of predicted maximal heart rate), or (3) moderate exercise (75% of predicted maximal heart rate) on three different days. In Experiment 2, 29 high-fit students (VO2 max ≥ 70th percentile) and 28 low-fit students (VO2 max ≤ 50th percentile) completed sedentary and light exercise conditions. In both experiments, free recall scores significantly increased in the exercise conditions compared with the sedentary condition, but JOL magnitude and metacognitive accuracy were largely unaffected. These results demonstrate that exercise can improve recall at both light and high intensities, and that the benefit can be obtained by individuals regardless of their fitness level.

Congruity influences memory and judgments of learning during survival processing.

A recent line of research has suggested that memory systems evolved to encode fitness-relevant information more effectively than other types of information-a phenomenon known as the "survival processing effect" (Nairne, Thompson, & Pandeirada Journal of Experimental Psychology: Learning, Memory, and Cognition 33:263-273, 2007). However, the basis for the effect has been debated. In addition, it is unknown whether or not individuals will adjust their judgments of learning (JOLs) to reflect the survival processing effect. In three experiments, participants rated 16 words for their relevance to a survival scenario and another 16 words for their relevance to a bank robbery scenario. In Experiment 1A (with no JOLs), the survival processing effect emerged; in Experiment 1B (with JOLs), no survival processing effect emerged, but JOLs were higher in the survival condition. In both cases, these findings were confounded by higher relevance ratings in the survival condition. In Experiment 2, relevance was manipulated within each list, and the survival processing effect was eliminated. Instead, both recall and JOL magnitude were related to level of congruity between the words and type of processing. Together, these results provide further evidence for the role of congruity in the survival processing effect and JOLs.

Cigarette abstinence impairs memory and metacognition despite administration of 2 mg nicotine gum.

The authors assessed the effects of cigarette abstinence (nonabstinent vs. minimum 8 hours abstinent) and nicotine gum (0 mg vs. 2 mg nicotine) on sustained attention, free recall, and metacognition using a within-subjects design. Moderate smokers (10 women and 22 men) received one training session followed by four test sessions on consecutive days. Nicotine gum improved sustained attention in both abstinent and nonabstinent states, but had no significant effect on predicted or actual recall levels. Cigarette abstinence significantly impaired free recall and reduced the magnitude of participants' predictions of their own performance. In addition, participants were significantly more overconfident about their future memory when abstinent. Thus, nicotine gum can improve smokers' performance in basic aspects of cognition (e.g., sustained attention) but may not alleviate the detrimental effects of cigarette abstinence on higher-level processes such memory and metacognition.

Stimulus and Response Expectancies Influence the Cognitive Effects of Cigarettes.

The pharmacological, stimulus expectancy, and response expectancy effects of light cigarettes (0.60 mg yield of nicotine) compared with virtually nicotine-free cigarettes (less than 0.05 mg yield of nicotine) were examined using a between-subjects design. A total of 103 college-student smokers completed tests of cognition before and after smoking one type of cigarette, which was evaluated on a number of dimensions. Cigarettes with nicotine were preferred on most dimensions, and stimulus expectancy partially mediated the relationship between nicotine and subjective effects of the cigarettes. Stimulus expectancy also mediated the effect of nicotine on tension reduction immediately after smoking, but not near the end of the experiment. Response expectancy effects of nicotine were related to predicted and actual recall performance, such that participants who performed well tended to attribute the effect to the cigarette they smoked. Implications for smoking cessation and research studies using non-nicotine cigarettes are discussed.

Expectancy and pharmacology influence the subjective effects of nicotine in a balanced-placebo design.

The expectancy and pharmacological effects of nicotine (0.60 mg) on memory and the subjective effects of cigarettes were examined by using a balanced-placebo design (i.e., expect either nicotine or no nicotine and receive either nicotine or no nicotine). A total of 120 college students who smoke were assigned to 1 of the 4 experimental groups, then rated the cigarettes on a number of dimensions and completed questionnaires on smoking urges, tension, and energy. Participants also completed tests of memory as well as predictions of memory. Pharmacology played a stronger role than expectancy in most ratings of the cigarettes, but significant effects of expectancy did emerge for feelings of increased wakefulness, concentration, calming, cigarette satisfaction, and hunger reduction. The presence of nicotine significantly reduced smoking urges, but expectancy alone reduced tension after smoking. Neither variable produced significant effects on memory or memory predictions. These findings demonstrate that nonpharmacological factors can play an important role in the self-reported effects of nicotine.

Improving the reliability of event-based laboratory tests of prospective memory.

Laboratory tests of event-based prospective memory (ProM) require participants to perform actions in response to infrequent cues in a background task. We conducted three experiments to assess and improve the reliability of this popular procedure. In Experiment 1, we tested college students on 2 separate days and found that the alternate-forms reliability of ProM accuracy was quite low (r = .31), although general knowledge accuracy was more reliable (r = .89). In Experiment 2, a statistically significant difference in reliability emerged between conditions with a low (n = 6) versus a high (n = 30) number of ProM targets. Finally, lower ProM accuracy increased reliability in Experiment 3. Adopting these straightforward changes may enhance the search for individual differences in ProM.

Processing similarity does not improve metamemory: evidence against transfer-appropriate monitoring.

The transfer-appropriate monitoring (TAM) hypothesis of metamemory predicts that judgment of learning (JOL) accuracy should improve when conditions during JOLs closely match conditions of the memory test. The authors devised 5 types of delayed JOLs for paired associates and varied them along with the type of memory test (cued recall or recognition). If the TAM hypothesis is correct, JOL and test type should interact to influence metamemory. Contrary to TAM, metamemory accuracy did not improve when JOL and test conditions matched but instead tended to vary according to whether the answer was apparent at time of JOL. Memory test scores and JOL magnitude were both greater when the correct target was evident during JOLs. Overall, the results are largely consistent with a monitoring retrieval view of delayed JOLs and do not support TAM as a viable account of JOL accuracy.

State-dependent memory effects using caffeine and placebo do not extend to metamemory.

The authors examined the impact of caffeine on human memory and predictions of memory (i.e., metamemory). On Day 1, 83 college students drank a sweetened beverage containing either caffeine (4 mg/kg body weight) or a placebo before they studied 40 pairs of words. While the participants studied, they predicted their future memory performance for each word pair. On Day 2, the participants again received caffeine or a placebo before the memory test. The participants who drank the same beverage on both days (either caffeine or a placebo) recalled more word pairs than did those who drank different beverages (caffeine on 1 day and a placebo on the other day). In contrast, memory predictions were more accurate when the beverages did not match on both days. These data provide evidence for state-dependent memory when caffeine is used, but not for state-dependent metamemory. People's memory and their predictions of memory can be influenced in different ways if they drink caffeine before they study or take a test.

Caffeine (4 mg/kg) influences sustained attention and delayed free recall but not memory predictions.

This experiment was conducted to examine the influence of a moderate dose of caffeine (4 mg/kg) on delayed memory, metamemory, and sustained attention. One hundred and forty-two volunteers ingested either caffeine or placebo during a study session which included three different memory tasks (free recall, cued recall, and recognition), and they made predictions of future memory performance. On day 2, participants again ingested either caffeine or placebo and completed memory tests. Sustained attention performance was measured on both days, and caffeine reliably improved hit rates and response latencies. A reliable drug-state interaction was detected only in the free recall test of memory. Caffeine did not affect the magnitude or accuracy of memory predictions, but there was some evidence that expectancies about caffeine were related to cognitive performance. Overall, caffeine's impact on memory and metamemory was not robust in this study. Copyright 2001 John Wiley & Sons, Ltd.