Effects of caffeine and glucose consumption on prefrontal cortex activity and cognitive performance

Caffeine is a psychoactive drug used to improve cognitive functions and is found in coffee, chocolate, various drinks and many medical treatments. Glucose is the most common dietary sugar in mammalian metabolism. Caffeine and glucose are used together in various products, especially energy drinks. In our research, the effects of single and combined consumption of caffeine and glucose on prefrontal cortex activity were investigated. 40 healthy male volunteers participated in the study. Subjects were examined in 4 groups: caffeine (200mg), glucose (25g), caffeine+glucose (200mg+25g) and empty capsule. Verbal memory, Stroop and N-back tests were used to compare cognitive performances. Prefrontal cortex activity during the tests was recorded with the functional near infrared ray spectroscopy (fNIRS) method. The test performances and fNIRS data of the subjects before and after taking the relevant substance (caffeine, sugar, etc.) were evaluated separately between and within the groups. As a result of the study, no effect of single or combined consumption of caffeine and glucose on verbal memory was observed. A significant decrease in reaction time was observed in subjects in the caffeine group due to caffeine consumption, compared to their first performance without caffeine. Subjects in the glucose group showed improvement in reaction time compared to their initial performance only in the demanding working memory task condition. The simultaneous consumption of caffeine and glucose had no effect on test performance. When test performances were evaluated between groups, no group showed a significant change compared to the control group. Hemodynamic activity of the prefrontal cortex during tasks showed several differences between the combined and individual consumption of caffeine and glucose.