Around 1800, Italian scientist Jean Aldini zapped the brains of dead felons with electricity to make their bodies move. He later reported using the same technique to cure "melancholy." This sounds like the history of electroconvulsive (shock) therapy, but those were actually the first experiments in transcranial direct-current stimulation (tDCS), tweaking the brain with very mild shocks, 1,000 times less intense than delivered by shock therapy. A resurgence in tDCS is now underway. (Experiment "Consent Video" above from the Berenson-Allen Center for Noninvasive Brain Stimulation.) Indeed, neuroscientists at the University of New Mexico are using a tDCS device powered by a 9-volt battery to see if 2 milliamps shocks to certain regions of the scalp can improve cognition and learning. Early results are promising. (In fact, tDCS may even prime neurons to respond to transcranial magnetic stimulation (TMS), a technique we've posted about on BB many times in which bursts from a magnetic coil near the head alter brain activity. TMS has been tested as a potential treatment for certain severe neurological and psychological disorders. Scientific journal Nature surveys the tDCS field in its latest issue. From Nature:
Last year a succession of volunteers sat down in a research lab in Albuquerque, New Mexico to play DARWARS Ambush!, a video game designed to train US soldiers bound for Iraq. Each person surveyed virtual landscapes strewn with dilapidated buildings and abandoned cars for signs of trouble – a shadow cast by a rooftop sniper, or an improvised explosive device behind a rubbish bin. With just seconds to react before a blast or shots rang out, most forgot about the wet sponge affixed to their right temple that was delivering a faint electric tickle. The volunteers received a few milliamps of current at most, and the simple gadget used to deliver it was powered by a 9-volt battery.
It might sound like some wacky garage experiment, but Vincent Clark, a neuroscientist at the University of New Mexico, says that the technique, called transcranial direct-current stimulation (tDCS), could improve learning. The US Defense Advanced Research Projects Agency funded the research in the hope that it could be used to sharpen soldiers' minds on the battlefield. Yet for all its simplicity, it seems to work.
Volunteers receiving 2 milliamps to the scalp (about one-five-hundredth the amount drawn by a 100-watt light bulb) showed twice as much improvement in the game after a short amount of training as those receiving one-twentieth the amount of current1. "They learn more quickly but they don't have a good intuitive or introspective sense about why," says Clark.
The technique, which has roots in research done more than two centuries ago, is experiencing something of a revival. Clark and others see tDCS as a way to tease apart the mechanisms of learning and cognition. As the technique is refined, researchers could, with the flick of a switch, amplify or mute activity in many areas of the brain and watch what happens behaviourally. The field is "going to explode very soon and give us all sorts of new information and new questions", says Clark. And as with some other interventions for stimulating brain activity, such as high-powered magnets or surgically implanted electrodes, researchers are attempting to use tDCS to treat neurological conditions, including depression and stroke. But given the simplicity of building tDCS devices, one of the most important questions will be whether it is ethical to tinker with healthy minds – to improve learning and cognition, for example. The effects seen in experimental settings "are big enough that they would definitely have real-world consequences", says Martha Farah, a neuroethicist at the University of Pennsylvania in Philadelphia.