A new study has found that coffee may gradually change the way the brain responds to touch and human body movements.
Millions around the world are accustomed to drinking a cup of coffee in the morning to get rid of drowsiness and fatigue, and to improve their ability to concentrate.
Normal doses of coffee (about one to two cups a day) contain between 50 and 400 mg of caffeine, but the effect of higher doses of this active ingredient on the sense of touch has remained a mystery until now.
In a new study, researchers assessed how normal and high doses of caffeine affect a specific brain process.
This process is evaluated using a method called "Short-Latency Afferent Inhibition", in which a mild electric shock is sent to the wrist moments before a magnetic pulse is sent to the brain.
The sensory signal from the wrist travels up the arm and into the somatosensory area of the brain. A fraction of a second later, the magnetic impulse strikes the adjacent motor cortex, causing the thumb to twitch.
To suppress this twitching, the brain typically requires a coordinated effort between specific chemical messengers within it. This brain process acts as a filtering system to keep movements smooth and controlled, preventing the brain from overreacting to every touch.
During the study, researchers assessed this filtration process in 20 healthy adults, each of whom received either 200 mg of caffeine or a placebo. The scientists then non-invasively stimulated the participants' motor cortex using magnetic pulses and measured how their brains responded.
They found that caffeine increased the brain's ability to restrict muscle response after exposure to touch, suggesting that coffee may "enhance" the short-latency incoming inhibition (SAI) process.
Researchers believe caffeine works by blocking adenosine receptor proteins in the brain. Blocking these receptors leads to an increase in acetylcholine, a chemical messenger that helps control how the senses and muscles work together.
The researchers wrote, "This finding is consistent with previous results indicating that choline-enhancing drugs, such as donepezil, also enhance short-latency feedback inhibition." They added, "Caffeine's effect may stem from its modulation of the cholinergic system (a vital nervous system that relies on the neurotransmitter acetylcholine (ACh) to transmit signals between neurons. This system plays a key role in controlling higher cognitive functions, regulating muscle movement, and managing autonomic functions)."
Scientists say these findings offer new insights into the physiological effects of caffeine and how it may be linked to disorders such as Alzheimer's and Parkinson's.
The researchers hope to conduct further studies with a larger number of volunteers, using more than 400 mg of caffeine.
They concluded by saying: "In light of the results discussed so far, people should continue to abstain from caffeine prior to short-latency incoming inhibition (SAI) assays."
