"What Caffeine Actually Does to Your Brain"

From Lifehacker:

For all of its wild popularity, caffeine is one seriously misunderstood substance. It's not a simple upper, and it works differently on different people with different tolerances—even in different menstrual cycles. But you can make it work better for you.


We've covered all kinds of caffeine "hacks" here at Lifehacker, from taking "caffeine naps" to getting "optimally wired." And, of course, we're obsessed with the perfect cup of coffee. But when it comes to why so many of us love our coffee, tea, soda, or energy drink fixes, and what they actually do to our busy brains, we've never really dug in.
While there's a whole lot one can read on caffeine, most of it falls in the realm of highly specific medical research, or often conflicting anecdotal evidence. Luckily, one intrepid reader and writer has actually done that reading, and weighed that evidence, and put together a highly readable treatise on the subject. Buzz: The Science and Lore of Alcohol and Caffeine, by Stephen R. Braun, is well worth the short 224-page read. It was released in 1997, but remains the most accessible treatise on what is and isn't understood about what caffeine and alcohol do to the brain. It's not a social history of coffee, or a lecture on the evils of mass-market soda—it's condensed but clean science.
What follows is a brief explainer on how caffeine affects productivity, drawn from Buzz and other sources noted at bottom. We also sent Braun a few of the questions that arose while reading, and he graciously agreed to answer them.

Caffeine Doesn't Actually Get You Wired

Right off the bat, it's worth stating again: the human brain, and caffeine, are nowhere near totally understood and easily explained by modern science. That said, there is a consensus on how a compound found all over nature, caffeine, affects the mind.

Every moment that you're awake, the neurons in your brain are firing away. As those neurons fire, they produce adenosine as a byproduct, but adenosine is far from excrement. Your nervous system is actively monitoring adenosine levels through receptors. Normally, when adenosine levels reach a certain point in your brain and spinal cord, your body will start nudging you toward sleep, or at least taking it easy. There are actually a few different adenosine receptors throughout the body, but the one caffeine seems to interact with most directly is the A1 receptor. More on that later.

Enter caffeine. It occurs in all kinds of plants, and chemical relatives of caffeine are found in your own body. But taken in substantial amounts—the semi-standard 100mg that comes from a strong eight-ounce coffee, for instance—it functions as a supremely talented adenosine impersonator. It heads right for the adenosine receptors in your system and, because of its similarities to adenosine, it's accepted by your body as the real thing and gets into the receptors.
Update: Commenter dangermou5e reminds us of web comic The Oatmeal's take on adenosine and caffeine. It's concise:

More important than just fitting in, though, caffeine actually binds to those receptors in efficient fashion, but doesn't activate them—they're plugged up by caffeine's unique shape and chemical makeup. With those receptors blocked, the brain's own stimulants, dopamine and glutamate, can do their work more freely—"Like taking the chaperones out of a high school dance," Braun writes in an email. In the book, he ultimately likens caffeine's powers to "putting a block of wood under one of the brain's primary brake pedals."

It's an apt metaphor, because it spells out that caffeine very clearly doesn't press the "gas" on your brain, and that it only blocks a "primary" brake. There are other compounds and receptors that have an effect on what your energy levels feel like—GABA, for example—but caffeine is a crude way of preventing your brain from bringing things to a halt. "You can," Braun writes, "get wired only to the extent that your natural excitatory neurotransmitters support it." In other words, you can't use caffeine to completely wipe out an entire week's worth of very late nights of studying, but you can use it to make yourself feel less bogged down by sleepy feelings in the morning....MORE