Several times a week, Harvard neurologist Alvaro Pascual-Leone takes control of someone else’s brain. He presses a device the size of a table tennis paddle against that person’s head and sends pulses of electricity that shut down or stimulate wide tracts of brain cells. The technique, called Transcranial Magnetic Stimulation, or TMS—apparently harmless and virtually painless—permits him to temporarily alter the activity of a living human brain.
Back in 1984, Pascual-Leone was involved in designing the first TMS system, which relies on a copper coil inside the paddle. The coil generates a magnetic field, inducing a current in any nearby conductor, such as the electrically active cells of the brain. Unlike shock therapy, which jolts the whole brain, TMS penetrates only an inch or so. The result can be as subtle as changing how the fingers move or as radical as causing temporary blindness.
TMS can be roughly aimed to explore diseases, like Alzheimer’s and Parkinson’s, that affect how the brain responds to the current, a change measurable through neuroimaging or electrodes placed on the scalp. TMS can also explore plasticity—the way neurons rewire themselves, take on new functions, or alter how they react to stimulation. By directly interfering with malfunctioning circuits, repetitive TMS is even being used to treat severe depression.
Discover spoke with Pascual-Leone in his office at the Harvard Berenson-Allen Center for Noninvasive Brain Stimulation about the future of TMS.
