Brain boost: A noninvasive way to electrically stimulate the brain, known as
transcranial direct current stimulation, has shown success in enhancing learning.
A little brain boost is something we could all use now and then. A new option may be on the horizon. Researchers at the National Institute for Neurological Disorders and Stroke, in Bethesda, MD, are studying how applying gentle electrical current to the scalp can improve learning.
Previous small-scale studies have suggested that a stream of current can improve motor function, verbal fluency, and even language learning. To explore how effective such stimulation can be as a learning tool, Eric Wassermann, a neuroscientist at the National Institute for Neurological Disorders and Stroke, is using an approach known as transcranial direct current stimulation (TDCS), in which an electrical current is passed directly to the brain through the scalp and skull. The technology for TDCS, which has been available for decades, is simple and fairly crude. (In the 1960s, it was used to improve mood in people with psychiatric disorders, although that effect hasn’t been repeated in more recent studies.) And in contrast to people undergoing electroconvulsive therapy, a seizure-inducing treatment used for severe depression that requires anesthesia, people undergoing TDCS feel just a slight tingle, if anything.
The device is simple: a nine-volt battery that’s been approved by the Food and Drug Administration for delivering drugs across the skin is connected to large flat sponges that are moistened and then applied to the head. It delivers a gentle 2 to 2.5 milliamps of current spread over a 20 to 50 square millimeter area of the scalp for up to 15 minutes. Little of that current actually reaches the brain–about half is shunted away from the target area, and the other half quickly dissipates as it gets farther from the scalp.
Wassermann’s team targets part of the brain known as the dorsolateral prefrontal cortex, a brain area involved in higher-level organization and planning, as well as in working memory. Because activity in this region has been shown in previous imaging Warren Grillstudies to predict an individual’s ability to recall information, the idea is that giving it an electrical boost will enhance memory function.
In preliminary results from the new study, which is part of a larger government-funded project to examine TDCS for cognitive enhancement, researchers found that direct current stimulation could improve memory in participants asked to learn and then recall a list of 12 words. The effect was significant in the early learning stages: in the first few trials, in which participants were given the same list over and over again, people in the treatment group could remember more words. But the learning curve for those working without the device quickly caught up to the zapped learners. “Now we want to see if we can enhance recall, not just encoding,” says Wassermann. “Ultimately, you’d just want to do the stimulation during encoding.”
Wassermann says that the preliminary studies are meant to help evaluate how practical the technology is. “We’re beginning to think about whether this technology has a role in cognitive enhancement in healthy people–whether it’s ethical, whether there is a need and a place for this,” he says. Wassermann originally became interested in noninvasive brain stimulation as a treatment for people with neurodegenerative disease, but a series of preliminary tests in patients have been unsuccessful. “It probably won’t work in a badly damaged brain,” he says. So his team is shifting its attention toward exploring transcranial stimulation as a learning tool in healthy people.
Very little is known about how TDCS works. Scientists theorize that the mild current primes the neurons for action but does not trigger the voltage spikes that neurons use to communicate. “Presumably, it is polarizing neurons and making them more or less likely to respond to inputs,” says Warren Grill, a neural engineer at Duke University, in Durham, NC. “But what’s happening at the level of the synapse, where the business of learning really takes place, we don’t know.”
Because the level of stimulation in TDCS is so low, it is considered safer than another noninvasive alternative, transcranial magnetic stimulation. In this approach, which is under investigation as a therapy for stroke and other brain disorders, an electric coil placed over the head generates a magnetic field that passes through the skull, exciting neurons in the brain below. However, because the procedure does trigger neural activity, it carries a risk of seizure.
Cognitive enhancement with drugs such as Ritalin, prescribed for attention deficit disorder, is already widespread, of course. A survey published online at Nature in April found that one in five respondents, most of whom were academics and scientists, reported using such drugs for nonmedical use. Electrical stimulation may prove even easier to access. “Half the people in this room could build this type of device with parts from RadioShack,” Wassermann told a crowd at a neurotechnology conference in Cleveland last week.