18 June 2021

Caffeine and Mental Acuity

 Uh-oh, coffee may not work. 

Warren’s pre-palpitations coffee intake, from Caffeine, Health and Memory (photo from multiple websites).

Welcome back. If you’ve been watching this space, you’ll recall that I’ve blogged about sleep, caffeine and memory on several occasions. Two posts that linked those subjects were Sleep and Memory, from 2012, and Caffeine, Health and Memory, from 2014.

The first reviewed the importance of slow-wave sleep over total sleep for pair-word tests, at least for younger adults; the second, that although caffeine might make you more alert, it has to come after not before you try to commit something to memory to help with remembering.

No doubt much has been learned since those posts appeared. That’s epitomized by a recently published study from researchers affiliated with Pittsburgh and Michigan State universities. They demonstrated that caffeine might help mitigate some cognitive deficits caused by lack of sleep; just don’t expect much a lift with higher level tasks.

Study Participants and Measurements
The researchers recruited and screened 276 undergraduates (ages 18 to 26, 66% female) to test the effects of caffeine on visual vigilant attention and on placekeeping following sleep deprivation.

Visual vigilant attention is the ability to maintain stable, visual alertness for sustained periods of time. The Psychomotor Vigilance Task (PVT) was used to measure the speed with which participants respond to a visual stimulus. The variable of interest is the participant’s rate of lapses, a lapse being a reaction time longer than 500 milliseconds.

Placekeeping is a cognitive control process required when a set of steps must be performed in a specified order despite interruptions. The measurement was made with the UNRAVEL task. UNRAVEL is an acronym identifying seven procedural steps performed in the order of the letters and starting over when L is reached. The variable of interest is the rate of placekeeping errors--steps performed in the wrong sequence. The researchers also recorded decision-rule errors--the correct step in the sequence but the incorrect response.

Example of two randomly generated stimuli from the UNRAVEL task. Stimuli offer no information about which step is to be performed and are often incongruent with the correct step or response. Below: The UNRAVEL rules for each step (letter) in the acronym and the correct keyboard responses for each rule based on the two stimuli above. The bolded letters represent possible response options for each rule. (from doi.apa.org/doiLanding?doi=10.1037%2Fxlm0001023)

Study Procedure
The participants arrived in the evening, completed sleepiness and mood assessments, UNRAVEL and PVT tasks, and were then randomly assigned to either a “sleep” or a “sleep-deprived” group.

Those in the sleep-deprived group stayed awake in the lab overnight. They were allowed to consume any food or beverage that did not contain caffeine or alcohol and to engage in quiet activities. Every two hours, they completed sleepiness and mood assessments. At three points (00:30, 04:30, and 08:30), they were given a capsule, the first two of which contained a placebo and the last, either a placebo or 200 mg of caffeine.

Participants in the sleep group returned the next morning and were randomly assigned to receive a capsule that contained either a placebo or 200 mg of caffeine.

All participants completed the morning sleepiness and mood assessments and UNRAVEL and PVT tasks.

Wrap Up
The researchers conducted three analyses to relate sleep or sleep-deprived conditions, placebo or caffeine, and visual vigilant attention (PVT) lapses or placekeeping (UNRAVEL) errors. They analyzed the data generated by all participants; repeated the analysis after excluding the small number (8%) of poor performers who were not following task instruction from the UNRAVEL assessment; and repeated the analysis after excluding the poorest performers from the PVT assessment.

They found that sleep deprivation impaired performance on both the PVT and UNRAVEL tasks. While caffeine improved performance on both tasks, when the poor performers were excluded from the UNRAVEL analysis, caffeine had no effect on UNRAVEL performance. In contrast, when the poorest performers were excluded from the PVT analysis, caffeine still affected PVT performance.

In summary, caffeine selectively improved visual vigilant attention but not, for the large majority of participants, the cognitive processes required for placekeeping. Again, that cup of coffee may not be enough for the tough stuff. Thanks for stopping by.


Study of caffeine’s effects on cognition caused by sleep deprivation in Jour. of Experimental Psychology: Learning, Memory, and Cognition: doi.apa.org/doiLanding?doi=10.1037%2Fxlm0001023
Article on study on EurekAlert! website: www.eurekalert.org/pub_releases/2021-05/msu-sdc052621.php

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