There’s all sorts of mumbo-jumbo about how sports drinks boost athletes’ performance, especially in endurance events such as yesterday’s Boston Marathon. But according to an intriguing new study, it isn’t the sports drinks’ calories (athletes benefit even if they spit out the drink rather than swallow it) or their sweet taste (drinks with artificial sweeteners do not boost performance). Instead, suggest Ed Chambers of the University of Birmingham and colleagues in a paper in The Journal of Physiology, carbohydrates in the drinks fit into receptors in the mouth that in turn activate the brain’s pleasure and reward centers, spurring athletes to push themselves harder without realizing how hard they're working.

For their study, the scientists prepared drinks containing either glucose (a sugar), maltodextrin (a tasteless carbohydrate) or plain water, mixed with artificial sweeteners so they tasted identical. Eight endurance cyclists rinsed their mouths for 10 seconds with one of the three drinks, and then got on a stationary bike. Results: athletes who swished with the glucose or maltodextrin drinks outperformed those on sweetened water by 2 to 3 percent, raising their pulse and sustaining a higher average power output—even though they said they didn’t feel they were working harder.

Chambers explains it this way: “Much of the benefit from carbohydrate in sports drinks is provided by signalling directly from mouth to brain rather than providing energy for the working muscles.”

That was born out by neuroimaging. Using fMRI to monitor brain activity after the athletes rinsed their mouths with one of the three drinks, the scientists found that glucose and maltodextrin increased activity in regions associated with reward or pleasure (the anterior cingulate cortex and striatum). The artificially sweetened water did not. They propose that the sugar or carbohydrate glommed onto receptors in the mouth, causing a signaling cascade that activated these brain regions, with the result that the athletes felt they were not working as hard as they actually were—contributing to endurance and power output. Once again, it seems as if the brain, not the muscles, ultimately govern how well we do even on what seems to be a purely physical task. As the scientists put it, “carbohydrate in the human mouth activates regions of the brain that can enhance exercise performance.”

For patients suffering from locked-in syndrome, in which they are completely paralyzed and able to do no more than blink their eyes, the greatest hope is not walking, not feeding themselves, not anything else having to do with moving: it is communicating. (An episode of House last month did a good job of depicting the horror of locked-in syndrome, which can be caused by amyotrophic lateral sclerosis, aka Lou Gehrig’s disease, brain-stem stroke or high spinal cord injury.) Hence the intense research effort to build brain-computer interfaces (BCI) for such patients. As a 2007 publication from the National Institutes of Health described a BCI system being developed there, “eight electrodes hitched to the computer . . . record the user’s electrical brain waves, which the computer analyzes and translates into specific commands, such as writing emails, selecting computer icons, or moving robotic devices. No surgery is required and users typically master the system within an hour or two.”

Writing emails is all well and good, but now brain-computer interfaces have made the big leagues: a BCI has been used to Tweet. Earlier this month Adam Wilson, a graduate student in biomedical engineering at the University of Wisconsin-Madison, sent “using EEG to send tweet.” He used what has become the standard methodology, in which EEGs pick up electrical signals from the brain and translate them into movements of a cursor, in this case on a screen with the 26 letters of the alphabet, as the scientists show in this video.

“The way this works is that all the letters come up, and each one of them flashes individually,” says Justin Williams, a UW-Madison assistant professor of biomedical engineering and Wilson’s adviser. “And what your brain does is, if you’re looking at the ‘R’ on the screen and all the other letters are flashing, nothing happens. But when the ‘R’ flashes, your brain says, ‘Hey, wait a minute. Something’s different about what I was just paying attention to.’ And you see a momentary change in brain activity.”

Although it’s a tedious process—Wilson likens it to texting, when you may have to press a key four times to get the desired character—people get better with practice. “I’ve seen people do up to eight characters per minute,” he says. Which just goes to show that Twitter is not the civilization-ending toy that so alarms some people: locked-in patients may be able to use it to give friends and families status updates merely by thinking.