Effects of Caffeine, sleep loss, and stress on cognitive performance and mood during U.S Navy SEAL training

Learning and Memory Lab Spring 2004


Effects of Caffeine, sleep loss, and stress on cognitive performance and mood during U.S Navy SEAL training

Caffeine is a widely used substance that has positive effect on mood, attention and performance requiring vigilance and cognition. It is used throughout the world by millions of people to help them stay alert during long working hours or to endure anticipated hours of performance with a lack of sleep. It is the most widely used psychoactive drug today and is a significant component of many soft drinks and medications (Barone and Roberts, 1996). When individuals are sleep deprived, many studies show caffeine to have favorable effects on their cognitive performance( Sawynok, 1995). Of course too much of anything can be bad for you and the habitual usage of caffeine lead to dependency and other tolerance syndromes. There have been many studies to link increased cognitive performance, attention, and vigilance with the use of caffeine for everyday stressors and sleep deprivation. However, it is the assertion of Lieberman, Tharion, Hale, Speckman and Tulley (2001) that few studies have examined the effects of caffeine during exposure of severe, multifactor stress to determine whether caffeine can be diffused in certain dosages to have effects on different levels of stress. The objective of their study was to examine the effects of moderate doses of caffeine on sleep deprivation and severe stressors as measured through that of U.S navy seals.


The subject pool was 68 all male SEALS, with a mean of 23. The subjects were informed before hell week of the study and instructed to sing a letter of consent. I No other forms of caffeine were allowed but that given by the study. The dependent variables are mood, cognition, and marksmanship outcomes. The independent variable is the doses of caffeine. The study was a double-blind placebo controlled study conducted in San Diego, California. The doses of caffeine were either 100, 200, or 300 mg or identical placebo capsules with sugar in them. Subjects were totally sleep deprived for 72 hrs before the dispensing of the substances. The subjects were given treatment, then regular duties commenced and afterwards tests were administered for 1hr and regular duties commenced again.

Saliva samples were taken to determine for caffeine consumption and changes. On computers, four cognitive tests were given. The scanning visual vigilance tests require subjects to find a stimulus that randomly appears on the computer screen. The four choice visual reaction time test presented a series of visual, stimuli at four separate locations and subjects had to indicate the correct location. The matching to sample test analyzed working memory. Whenever the words “ready” was presented on the screen subjects were instructed to press the down arrow key. The repeated acquisition test looks at motor learning and short-term memory. Subjects learned a sequence of 12 keys and each correct response fills in a visual image on the screen. Mood was assessed using the Profile of Mood States. This inventory has 65 adjectives related to mood on a five-point scale that is in response to the question of how the subjects were feeling at that moment. The Standford Sleepeiness Scale measured sleepiness, which is a seven item self-report scale. Lastly, rifle marksmanship was assessed with a simulator that consisted of a laser transmitter with a paper aiming target and a personal computer. A posttest questionnaire was also administered to determine whether volunteers thought they had been given caffeine or not. To determine the effects of hell week a within subjects ANOVA was conducted as well as all post hoc test. Observed frequencies were also assessed using frequency tables and analysis.


Dose-dependent changes in saliva caffeine existed with a positive correlation. All post hoc tests were significant at the p<. 05 level. There was no significant difference between the 100 mg dosage and placebo although all other dosages had significant differences compared to the placebo. Caffeine produced significant effects on visual vigilance, as the dosage was increased more targets were detected and response time decreased. The four choice visual reaction time tests also observed significant changes with an average tenfold decrease in error in the 200 and 300 mg dosage of caffeine. There