Caffeine enhances initial but not extended learning of a proprioceptive-based discrimination task in nonsmoking moderate users

No Enhancement of 24-Hour Visuomotor Skill Retention by Post-Practice Caffeine Administration

Caffeine is widely consumed throughout the world and appears to indirectly facilitate learning and memory through effects on attention and motivation. Animal work indicates that post-training caffeine administration augments inhibitory avoidance memory, spatial memory, and object memory. In humans, post-training caffeine administration enhances the ability to discern between familiar images and new, similar images. However, the effect of post-training caffeine administration on motor memory has not been examined. Therefore, we tested two groups of low caffeine consumers (average weekly consumption ≤500 mg) in a double-blind, placebo-controlled study involving acquisition of a continuous isometric visuomotor tracking skill. On Day 1, subjects completed 5 blocks (150 repetitions) of training on the continuous isometric visuomotor skill and subsequently ingested either 200 mg of caffeine or placebo. On day 2, subjects completed an additional 5 blocks of training. Day 1 mean performance and performance variability were both similar between groups, suggesting that both groups acquired the motor skill similarly. For mean performance on Day 2, patterns of re-learning, mean performance learning magnitudes, mean performance learning rates, and mean performance retention magnitudes were all similar between groups. For performance variability on Day 2, there was a small trend towards increased variability in the caffeine group during re-learning, but performance variability learning magnitudes and performance variability retention magnitudes did not differ between groups. Because motor skill acquisition can also be conceptualized as a reduction in performance variability, these results suggest that there may be a small negative effect of post-practice caffeine administration on memory of a newly-learned visuomotor skill. Overall, we found no evidence to suggest that post-training caffeine administration enhances 24-hour retention of a newly-learned continuous visuomotor skill, and these results support the notion that memory-enhancing effects of post-training caffeine ingestion may be task-specific.

Gender and impulsivity differences in licit substance use

Gender differences in ratings of impulsivity have shown increased impulsivity in men. Research also suggests higher impulsivity is correlated with increased use of alcohol, nicotine, and caffeine. In a large sample of young adults (N = 332), self-report data were collected on licit substance use and impulsivity/nonconformity. Among men, significant differences were found between higher and lower impulsivity groups for alcohol and caffeine use but not for nicotine use. Among women, significant differences were found between higher and lower impulsivity groups for alcohol and nicotine use but not for caffeine use. The data suggest the importance of recognizing gender differences in the relationship between personality factors and licit substance use.

Caffeine, but not time of day, increases whole-arm physiological tremor in non-smoking moderate users

1. Consumptive levels of caffeine significantly increased whole-arm physiological tremor in young adult males at 3 but not 1 mg caffeine/kg bodyweight. 2. Physiological tremor was not affected by time of day (TOD) or the interaction of caffeine and TOD. 3. Findings suggest that ingestion of a single oral dose of caffeine at typical consumptive levels results in measurable changes in physiological functioning and that whole-arm physiological tremor is a sensitive measure of physiological change due to drug effects. 4. However, the results suggest that whole-arm physiological tremor may not detect reliably TOD changes in functioning.