BOSTON, Mass. (August 26, 2009) — For over a century, scientists have been using electrical stimulation to explore and treat the human brain. The technique has helped identify regions responsible for specific neural functions—for instance, the motor cortex and pleasure center—and has been used to treat a variety of conditions from Parkinson’s disease to depression. Yet no one has been able to see what actually happens at the cellular level when the brain is electrically prodded.
Now, with the aid of optical imaging technology, researchers in the lab of HMS neurobiology professor Clay Reid have taken the first look at this process. They found that the neural response to electrical currents isn’t localized, as some had previously thought. That is, not all neurons immediately surrounding an electrode fire when a charge is delivered. Rather, a scattered and widely distributed set of neurons switch on. These findings, which will appear in the August 27 issue of Neuron, promise to end a longstanding debate about how neurons react to electrical stimulation.
Traditionally, observing neurons during electrical stimulation has been problematic. First author Mark Histed, a postdoctoral fellow in Reid’s lab, explains, "When you are stimulating electrically you are using relatively high voltages, and those high voltages make it almost impossible to record the very small currents that neurons produce."