David DiSalvo’s article “What Caffeine Really Does to Your Brain” in the August 2012 issue of Psychology Today, discusses how caffeine “plays” the ultimate mimic character of the inhibitory neurotransmitter adenosine. Adenosine is produced by neurons throughout the day and as they fire, and as more of it is produced, the more your nervous system ratchets down. Your nervous system monitors adenosine levels through receptors, particularly the A1 receptor that is found in your brain and throughout your body.
As the chemical passes through the receptors, your adenosine level increases until your nervous system balances it by “casting a spell” and putting you to sleep. Caffeine’s trick is to mimic adenosine’s shape and size, and enter the receptors without activating them. The caffeine treat occurs when the receptors are then effectively blocked (in clinical terms, caffeine is an antagonist of the A1 adenosine receptor). This is important not only because by blocking the receptors caffeine disrupts the nervous system’s monitoring of the adenosine level, but also because of the characters who “appear” as this is happening. Both dopamine and glutamate, the brain’s stimulants neurotransmitters, are freer to do their magical stimulating work with the adenosine levels on hold, and that’s the effect you feel not long after downing your triple shot latte.
So it’s not the caffeine that’s doing the stimulating. Instead, it’s keeping the doors blocked while the real “energy spirits” of the brain do what they love to do. As every good coffee drinker knows, this effect lessens over time. It increasingly takes more and more caffeine to achieve the same level of stimulation from your excitatory neurotransmitters otherwise “disguised” as your tolerance level.