In the study, researchers at the institute asked 103 volunteers to recall as many words that begin with a particular letter as possible. The researchers then passed a 2-milliamp current -- one-tenth of what is needed to power a small LED (light-emitting diode) light -- through electrodes attached to the surfaces of the volunteers' foreheads. When the volunteers were quizzed again while the current was still on, this time with a different letter, they were able to come up with 20 percent more words on average.
The findings could lead to new, drugless treatments for the symptoms of brain injuries and diseases, the researchers said.
"This could be a very helpful way of boosting brain function in people with brain disorders," said lead researcher Eric Wassermann, a neurobiologist with the National Institute's Brain Stimulation Unit in Bethesda, Maryland. "Drugs have more side effects and addictive potential. This doesn't seem to have those problems, at least at this point."
Though it's not clear exactly why a current boosts a person's verbal response, the research team believes it may allow cells in the prefrontal cortex, the region of the brain associated with verbal memory, to transmit signals more easily.
"What we think we're doing is changing the electrical environment of neurons and causing them to change their activity," said Wassermann.
Theoretically, the technique could also improve skills associated with other regions of the brain, he said.
It isn't the first time doctors and scientists have used electricity to modify the way the brain works. Some historians believe Greek physicians as early as the second century directed patients to apply a live torpedo fish, a type of electric ray, to the forehead as a cure for headaches.
More recently, scientists have tried using an electrode-free procedure known as transcranial magnetic stimulation to treat hallucinations and severe depression. But the process is considered risky because it can trigger seizures in some cases.
The National Institute's low-current technique does not seem to have this problem so far, but Wassermann cautions that more research is needed. "It's unknown whether chronically overdriving an impaired system might cause it to burn out faster," he said.
Still, Wassermann said he is excited about the doors that his team's discovery may open for cognitive science.
"This process is so easy to miniaturize that it essentially becomes wearable," he said. "One day, a patient could be wearing it in a hat with the power source in a bucket and turning it on perhaps at critical times of day."
But don't expect to be able to buy a "thinking cap" to help your kids with their homework anytime soon. Wassermann said he and his team only plan to focus on medical applications right now.
"The question of improving normal function is fraught with complexity," he said. "It's going to come up, obviously, but it's not something that I'm planning to do at this point."
