The study, published in Human Psychopharmacology: Clinical and Experimental, found that individuals who consumed caffeine and glucose in combination showed reduced brain activation associated with the task in the bilateral parietal cortex and the left prefrontal cortex – two regions that actively participate in attention and working memory processes.
“The reduced activity and the fact that no drop in behavioural performance was observed during the task suggests that the brain is more efficient under the combined effect of the two substances, since it needs fewer resources to produce the same level of performance than required by those subjects who were administered the placebo or who took only caffeine or glucose,” stated the researchers, led by Josep Serra Grabulosa, from the Department of Psychiatry and Clinical Psychobiology at the University of Barcelona, Spain.
“Our main finding is that the combination of the two substances improves cognitive performance in terms of sustained attention and working memory by increasing the efficiency of the areas of the brain responsible for these two functions”, explained Grabulosa.
Individually caffeine and glucose are known to have beneficial effects on cognitive performance.
Glucose is the major source of energy for the brain and is essential for the normal functioning of the central nervous system. Studies evaluating the cognitive effects of glucose have mainly been focused on its memory-improving action, where it has been shown that glucose can increase verbal long-term retrieval in women and produces improves performance in memory tasks in older adults.
The researchers noted that caffeine, on the other hand, is probably the most widely-used psychoactive substance around the world. Caffeine, which is found in coffee as well as in a wide variety of other drinks, has been found by pervious studies to increase subjective alertness and reduce fatigue, and have beneficial effects on reaction times.
Grabulosa and colleagues noted that although the positive effects of caffeine are well documented, controversy surrounds the relationship between regular consumption of caffeine and its beneficial effects.
Glucose and caffeine have both been shown to improve aspects of cognitive performance in previous studies – especially in processes relating to memory and attention. However, only a few studies have used functional magnetic resonance imaging (fMRI) to evaluate the effects of caffeine on working memory and attention processes and the effects of glucose on memory, and no studies have evaluated their combined effects.
“Our study attempted to overcome these limitations, using functional magnetic resonance imaging to examine known cerebral changes related to the combined caffeine and glucose beverage, showing the location and the degree of neural activation related to the sustained attention,” stated the researchers.
During the study, the researchers used fMRI to analyze brain activity during tasks aimed at evaluating sustained attention and working memory.
Participants were tested in a double-blind randomized design, after drinking a study beverage containing either, caffeine, glucose, the two combined, or a placebo consisting only of water
Results showed that the task performance in all four beverage subgroups was the same before and after the beverage. However, Grabulosa and co workers reported that although participants who received combined caffeine and glucose had similar performance to the others, they had a decrease in activation in the bilateral parietal and left prefrontal cortex.
“We found that subjects who received the two substances simultaneously performed similarly to the others, but with a decrease in activation in the areas related to the attention and memory processes. This could be interpreted as a synergistic effect since the same effect has not been found with the administration of glucose or caffeine separately,” wrote the researchers.
They added that since these areas have been related to the sustained attention and working memory processes, the new results “suggest that combined caffeine and glucose could increase the efficiency of the attentional system.”
However, Grabulosa and colleagues said that in order to confirm their findings, further studies are required to investigate the effects of combined glucose and caffeine using larger samples, different dosages of both substances, and controlling for different levels of cognitive effort.
Source: Human Psychopharmacology: Clinical and Experimental
Published online ahead of print, doi: 10.1002/hup.1150
“Glucose and caffeine effects on sustained attention: an exploratory fMRI study”
Authors: J.M. Serra-Grabulosa, A. Adan, C. Falcon, N. Bargallo