Effects of caffeine on the brain
Caffeine is the most consumed psychoactive substance, i.e. a substance which stimulates the central nervous system. It was estimated that about 80% of the world’s population consume caffeine every day. Caffeine is so popular, because of its stimulating effect on the brain. The consumption of caffeine may alleviate fatigue, increase the feeling of wakefulness and improve concentration and focusing.
Caffeine is known as an adenisine inhibitor. It blocks the adenosine receptors A2A and A1. This mechanism is the most significant as long as it starts working even after a single cup if coffee. A2b and A3 adenosine receptors are less likely to be involved.
Adenosine A1 receptors are found in in the thalamus, hippocampus, cerebral and cerebellar cortex. A2a receptors are less distributed. They are located in the striatum, nucleus accumbens and the olfactory tubercle.
There may be the connection between the A2a receptors and dopamine D2 receptors in the striatum. Some researches reported that adenosine A2a receptor antagonists are increasing the ability of dopamine D2 receptors to bind dopamine in the surface of striatal membranes.
When the caffeine blocks the receptors dopamine and glutamate (the brain’s own stimulants) are able to work without any obstacles.
It was estimated that 4-5 cups of coffee are able to inhibut the half of the adenosine receptors.
The other mechanisms via inhibition of phosphodiesterase or the blockage of GABA-A receptors require higher doses of caffeine, 20 or 40 times higher respectively.
100 times higher concentration is necessary to mobilize intracellular calcium depots, i.e. the caffeine may interfere with the uptake and accumulation of caffeine in striated muscles.
Caffeine increases the turnover of several monoamine neurotransmitters (5-hydroxytryptamine, dopamine, and noradrenaline).
Higher doses of caffeibe increases 5-hydroxytryptamine receptors, muscarinic receptors, and opioid receptors.
When consumed at higher doses, caffeine can also increase the utilization of glucose in the shell of the nucleus accumbens. This process results in the stimulation of other brain structures.
On the other hand caffeine stimulates the secretion of epinephrine (adrenaline) by the adrenal glands via stimulation of tge pituitary gland and secretion of adrenocorticotropic hormone. Epinephrine is known as a hormone responsible for the “fight or flight” reaction.
Probably, caffeine is increasing the level of serotonin in the brain. This fact explains the link between the lower risk of depression (in depression the activity and amount of serotonin is significantly lower) among those who consume caffeine.
Caffeine may activate the person’s frontal lobes and therefore lead to the arousal seen after tge consumption if coffee.
Effects of caffeine consumption
Caffeine causes the arousal of the central nervous system, provide the increase of alertness and wakefullness, increases concentration, reaction time, vigilance, and attention.
Despite the state of arousal no emotional changes related to pleasure or memory changes were reported. However, according to several studies, caffeine is able to enhance short-time memory.
Caffeine consumption may increase the brain’s sensitivity to color, light and sound.
Some studies suggest that regular consumption of caffeine (3-5 cups of coffee per day) may decrease the risk of developing Parkinson’s disease, Alzheimer’s disease as well as the other forms of dementia.
Effects on the sleep
Caffeine affects the brain structures involved in the control of sleep-wake rhythm such as locus ceruleus, reticular formation and raphe nuclei).
Mechanisms of addiction and withdrawal
When a person regularly consumes caffeine in great amounts, the body is trying to restore its normal functioning by creating more and more new adenosine receptors. This leads to caffeine tolerance – a person would need to consume more caffeine in order to reach the same effect as previously. So when the person stops consuming caffeine, adenosine binds with all of the receptors, including the new ones and therefore leads to the withdrawal. The more caffeine you ingest, the more severe would be the withdrawal symptoms.
About 12-24 hours after the last caffeine-containing drink occur the symptoms of caffeine withdrawal. The peak is seen between 20 and 51 hours. Until the 9th day of withdrawal the most severe symptoms are gone, although in some cases, they remain up to 12 days.