According to a study published in Scientific Reports, caffeine not only reduces drowsiness but can disrupt the detrimental impact of sleepiness on cognitive performance.
Many jobs rely on their personnel to perform important and complex tasks even in the wake of sleep deprivation. Personnel such as aircraft operators, truck drivers, police officers, and military workers often work long and intense shifts and regularly rely on caffeine to stay alert on the job.
In an initial study, researchers Eugene Aidman and his team found that sleep-deprived subjects who were given regular doses of caffeine performed better on a simulated driving task compared to subjects who were given no caffeine. Interestingly, the caffeine group also showed a weaker covariation between drowsiness and driving task performance — suggesting that the caffeine doses were reducing the impact of sleepiness on cognitive performance.
The researchers were motivated to further explore this effect in a second experimental, placebo-controlled study in a sleep laboratory. A final sample of 11 men and women between the ages of 18 and 28 took part in a 50-hour total sleep deprivation protocol. Five of the participants were given four 200 mg doses of caffeine every two hours, in the form of chewing gum (caffeine group). Six of the participants were given identical looking chewing gum at these same time points, but this gum contained no caffeine (placebo group).
Throughout the experiment, subjects were constantly surveyed and took part in 40-minute driving tasks using a driving simulator every three hours. During these driving tasks, drowsiness was assessed through infra-red glasses that monitored eyelid movement during blinks. Directly before and after performing the driving tasks, participants took part in four cognitive performance tests.
As expected, those who chewed the caffeinated gum were significantly less drowsy one hour after the first dose and remained less drowsy than the placebo group throughout the experiment. The caffeine group also reported lower ratings of sleepiness and irritability compared to the placebo group. However, the researchers note that the caffeine group still reached high-risk levels of drowsiness and reached a maximum drowsiness that was only 1.4 points lower than that of the placebo group.
Performance results for the cognitive tasks revealed that the caffeine group significantly outperformed the placebo group on the Psychomotor Vigilance Test (PVT) and the Procedural Reaction Time (PRT) task. Moreover, the researchers discovered a unique pattern of results among the caffeine group, where higher levels of drowsiness did not lead to a linear drop in task performance. Instead, the caffeine group showed a weakened relationship between drowsiness and cognitive performance.
This dissociation between drowsiness and task performance was greatest for the most complex task which involved executive functioning (a Go No-Go task) and approached significance for the PVT and PRT tasks. Aidman and colleagues say that this suggests that performance on more complex cognitive tasks may be guided by something more than level of alertness.
This study extended the researchers’ previous findings by including three additional cognitive tests. The researchers found convincing evidence that caffeine interrupts the relationship between drowsiness and cognitive performance and suggest that this moderating effect of caffeine should be further explored in future studies. Additional insight into how caffeine might counter the harmful effects of drowsiness would be helpful for those navigating challenging working conditions.
The study, “Caffeine may disrupt the impact of real‑time drowsiness on cognitive performance: a double‑blind, placebo‑controlled small‑sample study”, was authored by E. Aidman, M. Balin, K. Johnson, S. Jackson, G. M. Paech, M. Pajcin, C. Yates, E. Mitchelson, G. H. Kamimori, J. Fidock, C. Della Vedova, and S. Banks.