What does this part of the brain do, again?” I asked, pointing to the electrode on my right temple.

“That’s the right inferior frontal cortex,” said Vince Clark, the director of the University of New Mexico Psychology Clinical Neuroscience Center, in Albuquerque. “It does a lot of things. It evaluates rules. People get thrown in jail when it’s impaired. It might help solve math problems. You can’t really isolate what it does. It has emotional components.”

It was early December, and night was falling, though it was barely five. The shadows were getting longer in the lab. My legs felt unusually calm. Something somewhere was buzzing. Outside the window, a tree stood black against the deepening sky.

“Verbal people tend to get really quiet,” Clark said softly. “That’s one effect we noticed. And it can do funny things with your perception of time.”

The device administering the current started to beep, and I saw that twenty minutes had passed. As the current returned to zero, I felt a slight burning under the electrodes—both the one on my right temple and another, on my left arm. Clark pressed some buttons, trying to get the beeping to stop. Finally, he popped out the battery, the nine-volt rectangular kind.

This was my first experience of transcranial direct-current stimulation, or tDCS—a portable, cheap, low-tech procedure that involves sending a low electric current (up to two milliamps) to the brain. Research into tDCS is in its early stages. A number of studies suggest that it may improve learning, vigilance, intelligence, and working memory, as well as relieve chronic pain and the symptoms of depression, fibromyalgia, Parkinson’s, and schizophrenia. However, the studies have been so small and heterogeneous that meta-analyses have failed to prove any conclusive effects, and long-term risks have not been established. The treatment has yet to receive F.D.A. approval, although a few hospitals, including Beth Israel, in New York, and Beth Israel Deaconess, in Boston, have used it to treat chronic pain and depression.

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