How Does Caffeine Influence Our Brain

Yiwei Chen

Nutrition 11

6/1/14

How does caffeine influence our brain?

Since the seventeenth century, tea and coffee have become the most popular drinks as people recognized its ability to foster human’s productivity and cheer the spirits. Caffeine is discovered in a number of plants such as coffee beans, tea leaves, and cocao beans. Caffeine is a naturally occurring chemical stimulant called methylxanthine that can be found in coffee, tea, soft drinks, chocolate, kola nuts and certain medicines.  It is a common experience that our brain can be “turned on” by caffeine because it not only affects the body’s metabolism and but also stimulates the central nervous system, making people more alert and boost their energy.1 So, how does caffeine alter the functioning of human brain? Until the recent years, the neuroscientist came to understand the mechanics of caffeine. Adenosine receptors are the most important biochemical targets of caffeine.2 Adenosine acts as an inhibitory neurotransmitter, preventing neurons from firing excessively. Hence, adenosine suppresses activity in central nervous system.  Caffeine binds adenosine receptors and boost the brain’s own stimulants so that dopamine and glutamate can work freely. Glutamate is a neurotransmitter released by the nerve cells; it is responsible for excitation.

Very preterm infants often have a higher risk of apnea and death. Caffeine therapy is initiated to prevent premature infants from apnea. Recent Caffeine in Apnea of Prematurity (CAP) study has shown that the rates of cerebral palsy and cognitive delay were substantially reduced with caffeine treatment. White matter injury can be one factor of cerebral injury.3 White matter tissue, actively affecting how brain learns and functions, is where messages pass between different grey matter areas.  To investigate the function of the brain, Magnetic resonance imaging (MRI) is a technique that uses strong magnetic fields and radio waves to get images of the brain. The purpose of this metabolic study was to see if caffeine influenced white matter injury and development by using MRI. 70 infants who were considered suitable for caffeine therapy within the first 10 days were randomly allocated to either caffeine citrate (with a dose of 20mg/kg) or placebo. The researchers used the MRI to measure the white and gray matter abnormalities, global and regional brain volumes, and white matter microstructure. They also analyzed the white matter microstructure by line scan diffusion imaging. As a result, there were no significant differences between white or gray matter and global and regional brain volumes in both groups. But caffeine exposure appeared to alter the diffusion measures of the cerebral of white matter. This suggests that caffeine therapy can improve white matter microstructural development in preterm infants.

Caffeine can improve the white matter neurodevelopment in the immature human. But many adults consume caffeine to enhance their brain performance. Little do they know about the effects of caffeine in improving the memory performance. The purpose of this double-blind metabolic study was to examine the effects of caffeine on working memory (WM) during the encoding, maintenance and retrieval phase of memory task in middle-aged, male habitual caffeine consumers.4 21 healthy Dutch male participants (aged 40-61) were recruited for this study. To minimize the psychological effects of the performance, both the participants and experiments were not informed about the caffeine content of the coffee preparation. They were randomized to consume either an instant coffee with100mg of caffeine or a placebo with less than 3 mg caffeine. During the encoding phase, participants were instructed to memorize a letter string shown on the screen. The maintenance phase was designed for a cross fixation on the screen, and during the retrieval phase the participants responded whether the probe letter was part of the letter string they saw. The researchers acquired data of caffeine consumption and assessed the participants’ functional magnetic resonance imaging (fMRI) tasks. This study present evidence that load-related encoding activation was greater in the caffeine than the placebo condition, suggesting a direct effect of cognitive control of WM. Caffeine has an effect in the left thalamus during WM maintenance, indicating an effect on arousal. There was no difference between the caffeine and placebo groups during retrieval. These findings suggest that effects of drinking 1-1.5 cup of coffee may be contributed to both a direct and indirect effect on WM process.

Lots of studies have assessed the effect of caffeine consumption on the brain activation of young and middle-aged adults. Some researchers became curious about the effect of caffeine on the elderly. The purpose of the double-blinded metabolic study is to evaluate the impact of caffeine on the working memory-related brain activation during highly demanding cognitive task in the elderly.5 24 elderly individuals (mean age 68.8 ± 4.0 years, 17 females) participated in an experiment. In a prospective crossover design, half of the participants were assigned to take one capsule of 200 mg caffeine (approximately 2-2½ cups of coffee) at day 1 and placebo at day 2, while the other participants had placebo at day1 and caffeine at day 2. This was given 30 minutes before the experiment. Among a sequence of letters, participants need to identify the targeted letters that are identical to the letter presented before, for example “a f h f”. Participants gave response whether the letter was target or not in fMRI. Each task lasted 8-10 minutes, and each participant performs two tasks per day.  MR imagining scanner recorded the brain activities in the working memory network and visual areas during the experiment. After they collected the behavioral data and images, the researchers found that there was no significant difference in the response accuracy and time between the caffeine and placebo group. However, through the MR Imaging, the researchers observed that caffeine arouse higher activation in the bilateral striatum, an area has a great amount of adenosine receptor neurons but also in the frontoparietal areas that are known to be closely associated with working memory encoding process. These findings provided the evidence that caffeine revs up the brain as an activator of bold activation and functional connectivity in working memory-related in elderly individuals.