military, first responders, transport workers and factory shift workers. Repeated caffeine doses can help maintain physical and cognitive capabilities in these individuals and reduce failures and accidents at work. Keep in mind though that this is simply a preservation of abilities not a boost and should really only be used under circumstances of unavoidable fatigue.

Also, there is the suggestion that caffeine use in situations of reduced alertness really only preserves simple or very well rehearsed functions. So expecting caffeine to restore your full ability to think, reason and problem-solve during periods of fatigue is unrealistic.

Caffeine improves sports performance. Want more information about this — try the Sports Dietitians Australia website. Caffeine can cause anxiety and agitation with high doses. So this is an interesting one.

For example, one of the reasons I think I have never taken to coffee is that even small doses of caffeine usually make me feel agitated and unwell. Caffeine can improve learning and memory, sorta. So that coffee you have before attending your lectures probably will help you focus and remember some more of what you are told.

The evidence that caffeine improves memory and learning directly though is a bit sparse and contradictory. It appears that any learning or memory improvements associated with caffeine intake are primarily due to caffeine making you more alert and awake. You remember the material better cause you are more alert when you learn it.

So improvements in memory and learning from caffeine intake are most notable when you are tired, when the content is a bit boring and you lack interest or for older people whose overall energy levels might be lower.

I did however find an article that suggested caffeine intake following study can enhance the consolidation of long-term memories, so the exact effects of coffee on learning and memory are still an area of active research.

Caffeine may be protective against neurodegenerative diseases like Alzheimers. There is increasing evidence that moderate caffeine intake e. Caffeine can help analgese headaches. Whilst caffeine withdrawal can cause headaches, caffeine itself can improve headaches, especially when combined with popular pain relievers like aspirin, paracetamol and ibuprofen.

Caffeine narrows the blood vessels that feed the brain — supposedly that is the mechanism of action. However, because the withdrawal from caffeine can increase headaches, those who experience them regularly including migraines are sometimes recommended to abstain from too much caffeine.

Caffeine can improve your mood. Supposedly a coffee every 4 hours can sustain a measurable improvement in mood. In lower doses, caffeine induces a sense of calmness and interest. Increased intake is associated with a lower risk of depression.

It seems that outside of having a few too many leading to anxiety, nervousness , moderate coffee consumption is, on average, beneficial for mood.

e judgements, decision making, problem-solving. Caffeine can help you in passive or low complexity situations. But turn up the heat in terms of the complexity of the task, and caffeine is not really going to help you much.

Have a complex essay to write? Caffeine will help you stay awake, but not make you any better at essay writing. Individuals with ADHD are commonly given stimulant medications yes, it does seem a bit contradictory, but it works. As caffeine is a stimulant, it does provide some benefit to individuals with ADHD, but in no way better than prescribed medications.

Caffeine is less helpful to regular consumers of it. If you already consume a significant amount of caffeine, you will unlikely get much benefit from additional amounts. You are more likely to experience the effects of mild overdose anxiety, jitters, etc.

In fact, you are more likely to experience performance decrements if your caffeine intake falls. My reading of an admittedly small number of review articles suggests there are positive reasons to be a regular consumer of caffeine within guidelines.

This is particularly the case if you have unavoidable fatigue or tiredness arising from insufficient or irregular sleep patterns. For increasing alertness, concentration and focus, mood and learning caffeine seems to be an effective and safe method. Most of its effects are achieved through a general increase in arousal level, not an increase in intelligence or ability to work with and process information.

Twenty-four of the stems could be completed with words previously presented during the study phase, randomly intermixed with 12 word-stems from the non-studied list. Participants were instructed to complete the stem with the first word that came to mind.

The explicit word-stem cued recall task followed immediately, consisting of the remaining 24 word-stems corresponding to words from the study list. Participants were instructed to complete the word-stems with words they saw earlier during the pleasantness-rating task.

Priming was calculated by subtracting normative baseline completion rates collected by Ryan et al. Cued recall was measured as the percentage of study words correctly recalled. After completing both memory tasks, participants provided a final rating of how awake they felt.

Eligible participants were instructed not to eat or drink anything the morning of the experiment. They arrived at the laboratory between 6 and 7 a. Prepackaged instant coffee Starbucks Via Italian Bold caffeinated and decaffeinated was prepared using a standardized procedure to ensure that each 8-ounce cup contained the same amount of caffeine approximately mg in the caffeinated coffee, and mg in the decaffeinated coffee; Starbucks Corporation.

Participants were given the cup of coffee to drink, and then read a book for 30 min. To control for expectancy effects, all participants were told that the coffee was caffeinated, and the experimenter was blind to the type of coffee administered.

After 30 min, the implicit and explicit tasks were administered as described earlier. After completing the final wakefulness rating, participants were asked whether they felt that the coffee had affected them positively, negatively, or not at all.

Two participants, one from each group, were excluded because of extremely low explicit memory performance only one and two correct answers , suggesting that they either did not understand the task or did not follow instructions. Another participant was dropped due to missing MEQ questionnaire data.

To create an even number of participants in each condition, we randomly removed one additional participant in the decaffeinated group. The analyses were conducted on a final sample of 60 participants 30 in each group.

Participants who drank caffeinated coffee were significantly more awake by the end of the experiment, while participants who drank decaffeinated coffee did not experience the same increase in perceived wakefulness, as depicted in Figure 1A Morning. No participant reported that caffeine affected him or her negatively.

FIGURE 1. Change in perceived wakefulness across different points in Experiment 1 A and Experiment 2 B. Participants in the caffeinated group performed significantly better than the decaffeinated group on word-stem cued recall, but the groups did not differ on priming.

Results are depicted in Figure 2A Morning. FIGURE 2. Mean performance for cued recall and priming for Experiment 1 A and Experiment 2 B.

Priming scores were calculated by subtracting normative baseline completion rates Ryan et al. We examined this possibility by comparing memory performance within the decaffeinated group between those who did and did not report a positive effect of coffee.

Consuming caffeine increased explicit memory performance for college-aged adults during early morning hours. The result is consistent with our previous study Ryan et al.

However, caffeine had no effect on word-stem completion priming. The latter finding suggests that priming may not be influenced by manipulations of arousal. Next, we considered whether caffeine would result in the same increase in explicit memory performance during the afternoon as observed in the morning.

We expected that caffeine would not enhance explicit memory performance in the afternoon, since young adults are already at their physiological peak, and that caffeine would similarly have no effect on priming. Forty-three undergraduates were randomly assigned to the caffeinated group or decaffeinated group.

The procedures were identical to the morning session, except participants were tested between 2 and 4 p. Participants were instructed not to drink caffeinated beverages on the day of the experiment. Three participants were excluded because of extremely low explicit memory performance zero, one, and two correct answers , suggesting that they either did not understand the task or did not follow instructions.

The analysis was conducted on a final sample of 40 participants 20 in each group. Wakefulness ratings are depicted in Figure 1A Afternoon. In contrast to the morning testing session, caffeine did not influence either type of memory performance in young adults in the afternoon Figure 2A Afternoon.

We compared those individuals reporting a positive or non-positive neutral or negative effect of caffeine separately for the caffeinated and decaffeinated groups. In order to better understand the impact of caffeine at different times of day, we compared participants in the morning and afternoon testing sessions on wakefulness measures and memory measures.

Ingesting caffeine in the morning differentially affected how awake participants felt by the end of the experiment compared to ingesting caffeine in the afternoon.

Data were first analyzed with a mixed-factor 2 × 2 × 2 ANOVA comparing test type explicit, implicit , time of day morning, afternoon , and coffee type caffeinated, decaffeinated. The omnibus test was followed up with separate ANOVAs on explicit and implicit tests. Comparing the results of the explicit memory test across time of day, ingesting caffeine only improved explicit memory performance during the morning testing session.

These results further illustrate that the impact of caffeine on memory performance depended on the time of the testing session — explicit memory was only enhanced by caffeine during the morning testing session.

Regardless of coffee type, participants had higher implicit memory performance priming in the morning compared to the afternoon. Additionally, caffeine had no effect on priming scores. In Experiment 2, we consider whether the observed improvement in explicit memory performance was due specifically to the ingestion of caffeine, or from the non-specific effect that caffeine has on increasing physiological arousal.

To determine the specificity of the caffeine effect, participants in Experiment 2 engaged in cardiovascular exercise during the early morning, their non-optimal time of the day. Even short sessions of exercise reliably elevate physiological arousal Hung et al.

Acute exercise increases the concentration of catecholamines in the brain including dopamine, epinephrine, and norepinephrine in the locus coeruleus Cooper, ; McMorris et al. Just as caffeine acts on the locus coerulus to increase wakefulness, exercise increases norepinephrine in the locus coeruleus, which in turn induces arousal Dietrich and Audiffren, If caffeine benefits explicit memory by increasing general physiological arousal, we would expect to see the same boost in memory performance after morning exercise.

Since previous work suggested that implicit memory is optimal during low arousal times of the day May et al. Forty undergraduates participated in a session conducted between 6 and 8 a. They were instructed not to eat or drink anything but water on the morning of the experiment.

Participants were informed they could withdraw at any time if they were unable to complete the required exercise. Upon arrival, participants provided a wakefulness rating on a scale from -5 not awake to 5 wide awake. Then, they were equipped with an activity watch New Balance Duo Sport Monitor, Durham, NC that records heartbeats per minute.

Participants practiced measuring their heart rate with the watch. A baseline heart rate measure was taken once the participant could operate the device. Participants completed approximately 15 min of cardiovascular exercise exercise group or a gentle stretching routine stretching group.

For the exercise group, cardiovascular exercise was defined as 10 min of exercise with a 20 percent or greater increase in heart rate from baseline. Participants achieved this by performing interval laps of running up a set of stairs and briskly walking down another set of stairs at the other end of the hallway.

An experimenter was stationed at the end of each lap to record heart rate. In the stretching group, participants completed 15 min of a simple stretching routine.

Experimenters demonstrated all the stretches and recorded heart rates at 1-min intervals. After completing either the exercise or stretching protocol, participants gave a second rating of wakefulness and returned to the laboratory for memory testing.

Heart rate was calculated as the average across 15 min of activity and compared to baseline heart rate. Participants who completed the exercise protocol reported feeling significantly more awake immediately following the activity compared to the stretching condition, depicted in Figure 1B.

Exercise did not have an impact on either explicit or implicit memory during the early morning, despite participants feeling more awake after exercise Figure 2B. Consuming caffeinated coffee results in significantly higher memory performance on an explicit cued—recall task in the early morning, but not in the late afternoon.

These results are consistent with the hypothesis that caffeine benefits cognition during suboptimal conditions Ryan et al. Importantly, the benefits of caffeine for explicit memory performance do not appear to be related to an acute increase in physiological arousal Experiment 2 , to the perception of being more awake and energized after ingesting coffee Experiment 1 , or general expectancy effects since participants in Experiment 1 were all told they were consuming caffeinated coffee.

We were somewhat surprised by the finding that elevating arousal through exercise during the morning did not improve explicit memory performance, particularly since participants consistently reported feeling more awake and energized after exercise. Our finding is consistent, however, with research suggesting that the cognitive benefits of exercise build gradually, rather than acutely.

For example, Bugg et al. These authors argue that habitual exercise leads to increased calcium levels, which are necessary for the metabolism of dopamine and norepinephrine. This increase in calcium occurs gradually and is maintained through consistent exercise. In contrast, caffeine results in a fast blockade of adenosine receptors, preventing the blockade of norepinephrine McGaugh, , which may influence the consolidation of new memories.

The difference in the timeline of the effects of caffeine and exercise may explain why a single cup of coffee benefits memory and acute exercise does not. Given that participants were not morning-type individuals, it is not surprising that they tended to go to bed late even though they were scheduled for the early morning testing condition.

Accordingly, the young adults tested during their non-optimal time of day the morning reported fewer hours of sleep than those who were tested during their optimal time of day in the afternoon. The difference in sleep time between the morning and afternoon testing conditions likely reflects the real-world situation for college students.

This decrease in sleep adds to, or may even account for, the impact of circadian rhythms on cognitive functioning in young adults. Importantly, however, morning participants did not differ in the number of hours slept between the caffeinated and decaffeinated conditions, and these individuals did not differ from participants in the exercise and stretching conditions.

The only difference between all morning testing groups that had an impact on memory performance was the administration of caffeine. The mechanisms by which caffeine enhances explicit memory remain unclear. Recently, Borota et al. They found that caffeine ingested immediately after studying a series of object pictures resulted in better discrimination between old objects and visually similar lures, but not better recognition performance per se , suggesting a specific effect of caffeine on pattern separation.

Consistent with our findings, the authors conclude that the benefit of caffeine is not merely due to general increases in arousal and attention. Memory enhancement may be mediated by increases in levels of norepinephrine that have been shown to benefit pattern separation Segal et al.

Multiple forms of implicit learning, including repetition priming, are thought to rely on cortical adaptations that are independent of the hippocampus for review, see Reber, This cannot be the whole story, however. It could be that participants in afternoon caffeine experiment did not follow our instructions to refrain from consuming caffeinated beverages on the day of the experiment, and thus an additional mg of caffeine made no difference to memory performance.

A third possibility, discussed earlier, is that caffeine was effective because morning participants had fewer hours of sleep the night before testing, compared to afternoon participants.

Adan et al. However, Adan et al. It is important to note, however, that unlike our previous work examining memory and time of day in older adults Ryan et al. Instead, explicit memory performance did not differ between the decaffeinated groups in the morning and afternoon. It is unclear whether testing the same individuals in the morning and the afternoon would have shown the expected time of day effect in explicit memory, although we note that other researchers have reported the effect using between-subjects designs e.

In summary, our results suggest that caffeine results in explicit memory enhancement for young adults during their non-optimal time of day — early morning. Although it is well documented that very few young adults perform best in the morning Chelminski et al.

For example, Randler and Schaal found that grade point average was negatively correlated with MEQ scores — the more a student preferred evening hours, the worse grades they earned in school.

The degree to which this effect is due specifically to differences in circadian rhythms or the lack of sleep that likely occurs among these students is unclear.

Nevertheless, it appears that for these students, caffeine has a benefit for learning. It remains to be seen whether consuming caffeine would result in better learning, whether newly learned information is maintained over time, and whether this effect could translate into real increases in academic achievement.

SS, TB, and LR developed the concept of the study and all authors were involved in study design. SS, EB, and TB collected and processed the data. All authors planned and performed data analyses. All authors wrote components of the manuscript and approved the final version. This work was supported by the Undergraduate Research Grant from the Honors College at the University of Arizona.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer FP and the handling Editor declared their shared affiliation, and the handling Editor states that the process nevertheless met the standards of a fair and objective review.

Adan, A. Early effects of caffeinated and decaffeinated coffee on subjective state and gender differences. Psychiatry 32, — doi: PubMed Abstract CrossRef Full Text Google Scholar.

Effects of caffeine and glucose, alone and combined, on cognitive performance. Anderson, M. Individual differences in the effect of time of day on long-term memory access.

CrossRef Full Text Google Scholar. Bailey, S. Circadian rhythmicity of cortisol and body temperature: morningness-eveningness effects. Borota, D. Post-Study Caffeine Administration Enhances Memory Consolidation in Humans.

London: Nature Publishing Group. Brice, C. The effects of caffeine on simulated driving, subjective alertness and sustained attention. Bugg, J.

Working memory performance. Aging Res. Capek, S. Chelminski, I. Horne and Ostberg questionnaire: a score distribution in a large sample of young adults. Cooper, C. Anatomical and physiological mechanisms of arousal with specific reference to the effects of exercise.

Ergonomics 16, — Delpouve, J. Cortex 58, 18—

In a previous study, we considered whether caffeine could overcome the well-documented decrease in memory performance among older adults during the late afternoon, when most older adults experience their circadian low point for review see: May et al.

We found that a single cup of coffee, ingested 30 min prior to memory testing, completely reversed the memory decline experienced by older adults in the afternoon Ryan et al. We suggested that caffeine might influence memory performance by boosting general levels of arousal during non-optimal times of day.

Our previous study suggested two things. First, caffeine should have the same memory-boosting effect for young adults in the early morning, when most young adults are at their physiological low point.

Second, we hypothesized that the effect was not due to caffeine specifically but should occur regardless of the method used to increase physiological arousal, such as engaging in physical exercise.

To determine the specificity of the caffeine effect, we also compared two types of exercise in the early morning — vigorous aerobic exercise versus gentle stretching — on memory performance.

A secondary goal of the study was to consider the effect of caffeine on two different forms of memory, the deliberate recall of information explicit memory and the unintentional recall of previously learned information implicit memory. Previous research suggests that while explicit memory scores are lower in young adults in the morning compared to the afternoon, priming scores actually increase during this period of low arousal, suggesting that explicit and implicit memory may be moderated differently by physiological arousal May et al.

Taken together, based on previous work, we expected that a caffeine would boost explicit memory performance in young adults during the early morning while impairing priming, b caffeine would have no effect on either explicit memory or priming during the afternoon, and c vigorous exercise, but not gentle stretching, would have the same impact on memory performance as caffeine during early morning hours.

Undergraduates from the University of Arizona ages participated in the study. Participants were excluded with a history of substance abuse or neurological or psychiatric disorders that might interfere with normal cognitive function.

Only those who consumed at least a moderate amount of caffeine on a weekly basis were enrolled in the study. Participants were also asked four key questions from the Morningness-Eveningness Questionnaire MEQ; Horne and Ostberg, to exclude young adults who preferred mornings.

Participant characteristics for all three experiments are presented in Table 1. All participants provided written informed consent that was approved by the Institutional Review Board at the University of Arizona.

Not surprisingly, number of hours slept the night prior to testing differed depending on the time of day. In Experiment 1, participants in the morning condition slept fewer hours compared to participants in the afternoon condition. Seventy-two unique three-letter word-stems and completions e.

Each stem could be completed with a minimum of five words. Each completion was letters in length and was not the most frequent completion for the stem. The lists were divided into three lists of 24 words, so that average word length and completion base rates were similar across the lists.

Two lists were used during the study and test phase. The third list served as fillers during the tasks. The lists were counterbalanced across tasks and experimental conditions.

Upon arrival, participants reported how awake they felt on a scale from 1 to 5 1- not awake, 5- wide awake. After the experimental intervention see specific experiments below , participants were shown 48 words two of the three study lists on a computer screen, one at a time.

Two filler words were added at the beginning and end of the list to control for primacy and recency effects. Words were presented in random order for 3 s each. Participants were instructed to rate the pleasantness of the words on a scale from 1 to 5 1- very unpleasant, 5- very pleasant as the experimenter recorded their verbal responses.

Participants were not informed that a memory test would follow later on. During a 5-min interval, participants completed the full version of the MEQ and reported the time they went to bed the night before the experiment and when they woke up in the morning. They completed a second rating of how awake they felt and were asked whether they ate or drank anything before the experiment.

In the test phase, the implicit memory task always preceded the explicit task. During the implicit word-stem completion task, thirty-six stems were presented on the computer screen, one at a time e. Twenty-four of the stems could be completed with words previously presented during the study phase, randomly intermixed with 12 word-stems from the non-studied list.

Participants were instructed to complete the stem with the first word that came to mind. The explicit word-stem cued recall task followed immediately, consisting of the remaining 24 word-stems corresponding to words from the study list.

Participants were instructed to complete the word-stems with words they saw earlier during the pleasantness-rating task. Priming was calculated by subtracting normative baseline completion rates collected by Ryan et al. Cued recall was measured as the percentage of study words correctly recalled.

After completing both memory tasks, participants provided a final rating of how awake they felt. Eligible participants were instructed not to eat or drink anything the morning of the experiment.

They arrived at the laboratory between 6 and 7 a. Prepackaged instant coffee Starbucks Via Italian Bold caffeinated and decaffeinated was prepared using a standardized procedure to ensure that each 8-ounce cup contained the same amount of caffeine approximately mg in the caffeinated coffee, and mg in the decaffeinated coffee; Starbucks Corporation.

Participants were given the cup of coffee to drink, and then read a book for 30 min. To control for expectancy effects, all participants were told that the coffee was caffeinated, and the experimenter was blind to the type of coffee administered. After 30 min, the implicit and explicit tasks were administered as described earlier.

After completing the final wakefulness rating, participants were asked whether they felt that the coffee had affected them positively, negatively, or not at all. Two participants, one from each group, were excluded because of extremely low explicit memory performance only one and two correct answers , suggesting that they either did not understand the task or did not follow instructions.

Another participant was dropped due to missing MEQ questionnaire data. To create an even number of participants in each condition, we randomly removed one additional participant in the decaffeinated group.

The analyses were conducted on a final sample of 60 participants 30 in each group. Participants who drank caffeinated coffee were significantly more awake by the end of the experiment, while participants who drank decaffeinated coffee did not experience the same increase in perceived wakefulness, as depicted in Figure 1A Morning.

No participant reported that caffeine affected him or her negatively. FIGURE 1. Change in perceived wakefulness across different points in Experiment 1 A and Experiment 2 B. Participants in the caffeinated group performed significantly better than the decaffeinated group on word-stem cued recall, but the groups did not differ on priming.

Results are depicted in Figure 2A Morning. FIGURE 2. Mean performance for cued recall and priming for Experiment 1 A and Experiment 2 B. Priming scores were calculated by subtracting normative baseline completion rates Ryan et al.

We examined this possibility by comparing memory performance within the decaffeinated group between those who did and did not report a positive effect of coffee. Consuming caffeine increased explicit memory performance for college-aged adults during early morning hours.

The result is consistent with our previous study Ryan et al. However, caffeine had no effect on word-stem completion priming. The latter finding suggests that priming may not be influenced by manipulations of arousal. Next, we considered whether caffeine would result in the same increase in explicit memory performance during the afternoon as observed in the morning.

We expected that caffeine would not enhance explicit memory performance in the afternoon, since young adults are already at their physiological peak, and that caffeine would similarly have no effect on priming.

Forty-three undergraduates were randomly assigned to the caffeinated group or decaffeinated group. The procedures were identical to the morning session, except participants were tested between 2 and 4 p. Participants were instructed not to drink caffeinated beverages on the day of the experiment.

Three participants were excluded because of extremely low explicit memory performance zero, one, and two correct answers , suggesting that they either did not understand the task or did not follow instructions.

The analysis was conducted on a final sample of 40 participants 20 in each group. Wakefulness ratings are depicted in Figure 1A Afternoon. In contrast to the morning testing session, caffeine did not influence either type of memory performance in young adults in the afternoon Figure 2A Afternoon.

We compared those individuals reporting a positive or non-positive neutral or negative effect of caffeine separately for the caffeinated and decaffeinated groups. In order to better understand the impact of caffeine at different times of day, we compared participants in the morning and afternoon testing sessions on wakefulness measures and memory measures.

Ingesting caffeine in the morning differentially affected how awake participants felt by the end of the experiment compared to ingesting caffeine in the afternoon.

Data were first analyzed with a mixed-factor 2 × 2 × 2 ANOVA comparing test type explicit, implicit , time of day morning, afternoon , and coffee type caffeinated, decaffeinated.

The omnibus test was followed up with separate ANOVAs on explicit and implicit tests. Comparing the results of the explicit memory test across time of day, ingesting caffeine only improved explicit memory performance during the morning testing session.

These results further illustrate that the impact of caffeine on memory performance depended on the time of the testing session — explicit memory was only enhanced by caffeine during the morning testing session.

Regardless of coffee type, participants had higher implicit memory performance priming in the morning compared to the afternoon. Additionally, caffeine had no effect on priming scores.

In Experiment 2, we consider whether the observed improvement in explicit memory performance was due specifically to the ingestion of caffeine, or from the non-specific effect that caffeine has on increasing physiological arousal. To determine the specificity of the caffeine effect, participants in Experiment 2 engaged in cardiovascular exercise during the early morning, their non-optimal time of the day.

Even short sessions of exercise reliably elevate physiological arousal Hung et al. Acute exercise increases the concentration of catecholamines in the brain including dopamine, epinephrine, and norepinephrine in the locus coeruleus Cooper, ; McMorris et al.

Just as caffeine acts on the locus coerulus to increase wakefulness, exercise increases norepinephrine in the locus coeruleus, which in turn induces arousal Dietrich and Audiffren, If caffeine benefits explicit memory by increasing general physiological arousal, we would expect to see the same boost in memory performance after morning exercise.

Since previous work suggested that implicit memory is optimal during low arousal times of the day May et al. Forty undergraduates participated in a session conducted between 6 and 8 a. They were instructed not to eat or drink anything but water on the morning of the experiment.

Participants were informed they could withdraw at any time if they were unable to complete the required exercise. Upon arrival, participants provided a wakefulness rating on a scale from -5 not awake to 5 wide awake.

Then, they were equipped with an activity watch New Balance Duo Sport Monitor, Durham, NC that records heartbeats per minute. Participants practiced measuring their heart rate with the watch.

A baseline heart rate measure was taken once the participant could operate the device. Participants completed approximately 15 min of cardiovascular exercise exercise group or a gentle stretching routine stretching group. For the exercise group, cardiovascular exercise was defined as 10 min of exercise with a 20 percent or greater increase in heart rate from baseline.

Participants achieved this by performing interval laps of running up a set of stairs and briskly walking down another set of stairs at the other end of the hallway.

An experimenter was stationed at the end of each lap to record heart rate. In the stretching group, participants completed 15 min of a simple stretching routine. Experimenters demonstrated all the stretches and recorded heart rates at 1-min intervals.

After completing either the exercise or stretching protocol, participants gave a second rating of wakefulness and returned to the laboratory for memory testing. Heart rate was calculated as the average across 15 min of activity and compared to baseline heart rate. Participants who completed the exercise protocol reported feeling significantly more awake immediately following the activity compared to the stretching condition, depicted in Figure 1B.

Exercise did not have an impact on either explicit or implicit memory during the early morning, despite participants feeling more awake after exercise Figure 2B. Consuming caffeinated coffee results in significantly higher memory performance on an explicit cued—recall task in the early morning, but not in the late afternoon.

These results are consistent with the hypothesis that caffeine benefits cognition during suboptimal conditions Ryan et al. Importantly, the benefits of caffeine for explicit memory performance do not appear to be related to an acute increase in physiological arousal Experiment 2 , to the perception of being more awake and energized after ingesting coffee Experiment 1 , or general expectancy effects since participants in Experiment 1 were all told they were consuming caffeinated coffee.

We were somewhat surprised by the finding that elevating arousal through exercise during the morning did not improve explicit memory performance, particularly since participants consistently reported feeling more awake and energized after exercise.

Our finding is consistent, however, with research suggesting that the cognitive benefits of exercise build gradually, rather than acutely. For example, Bugg et al. These authors argue that habitual exercise leads to increased calcium levels, which are necessary for the metabolism of dopamine and norepinephrine.

This increase in calcium occurs gradually and is maintained through consistent exercise. In contrast, caffeine results in a fast blockade of adenosine receptors, preventing the blockade of norepinephrine McGaugh, , which may influence the consolidation of new memories.

The difference in the timeline of the effects of caffeine and exercise may explain why a single cup of coffee benefits memory and acute exercise does not.

Given that participants were not morning-type individuals, it is not surprising that they tended to go to bed late even though they were scheduled for the early morning testing condition. Accordingly, the young adults tested during their non-optimal time of day the morning reported fewer hours of sleep than those who were tested during their optimal time of day in the afternoon.

The difference in sleep time between the morning and afternoon testing conditions likely reflects the real-world situation for college students. This decrease in sleep adds to, or may even account for, the impact of circadian rhythms on cognitive functioning in young adults.

Importantly, however, morning participants did not differ in the number of hours slept between the caffeinated and decaffeinated conditions, and these individuals did not differ from participants in the exercise and stretching conditions. The only difference between all morning testing groups that had an impact on memory performance was the administration of caffeine.

The mechanisms by which caffeine enhances explicit memory remain unclear. Recently, Borota et al. They found that caffeine ingested immediately after studying a series of object pictures resulted in better discrimination between old objects and visually similar lures, but not better recognition performance per se , suggesting a specific effect of caffeine on pattern separation.

Consistent with our findings, the authors conclude that the benefit of caffeine is not merely due to general increases in arousal and attention. Memory enhancement may be mediated by increases in levels of norepinephrine that have been shown to benefit pattern separation Segal et al. Multiple forms of implicit learning, including repetition priming, are thought to rely on cortical adaptations that are independent of the hippocampus for review, see Reber, This cannot be the whole story, however.

It could be that participants in afternoon caffeine experiment did not follow our instructions to refrain from consuming caffeinated beverages on the day of the experiment, and thus an additional mg of caffeine made no difference to memory performance.

A third possibility, discussed earlier, is that caffeine was effective because morning participants had fewer hours of sleep the night before testing, compared to afternoon participants.

Adan et al. However, Adan et al. It is important to note, however, that unlike our previous work examining memory and time of day in older adults Ryan et al.

Instead, explicit memory performance did not differ between the decaffeinated groups in the morning and afternoon. It is unclear whether testing the same individuals in the morning and the afternoon would have shown the expected time of day effect in explicit memory, although we note that other researchers have reported the effect using between-subjects designs e.

In summary, our results suggest that caffeine results in explicit memory enhancement for young adults during their non-optimal time of day — early morning. Although it is well documented that very few young adults perform best in the morning Chelminski et al.

For example, Randler and Schaal found that grade point average was negatively correlated with MEQ scores — the more a student preferred evening hours, the worse grades they earned in school. The degree to which this effect is due specifically to differences in circadian rhythms or the lack of sleep that likely occurs among these students is unclear.

Nevertheless, it appears that for these students, caffeine has a benefit for learning. The larger improvement of performance in fatigued subjects confirms that caffeine is a mild stimulant.

Caffeine has also been reported to prevent cognitive decline in healthy subjects but the results of the studies are heterogeneous, some finding no age-related effect while others reported effects only in one sex and mainly in the oldest population.

In conclusion, it appears that caffeine cannot be considered a ;pure' cognitive enhancer. Its indirect action on arousal, mood and concentration contributes in large part to its cognitive enhancing properties.

Abstract The effects of caffeine on cognition were reviewed based on the large body of literature available on the topic. Publication types Review. Substances Central Nervous System Stimulants Caffeine.