One of the first things neuroscience students learn is that the brain’s right hemisphere controls the left side of the body, and vice versa. Brain-computer interfaces, which employ brain signals to control an external device such as a robotic arm or a wheelchair, also utilize these opposing-side signals. Such technology is therefore unable to help victims of stroke and brain trauma, who often have one seriously damaged hemisphere that cannot be enlisted for motor commands.

But scientists now think they may be able to work around that limitation. Emerging research suggests that in addition to controlling the opposite side of the body, a given hemisphere allocates about 10 to 15 percent of its neurons to controlling the same side. A team led by neurosurgeon Eric Leuthardt of the Washington University School of Medicine in St. Louis has shown for the first time that these same-side signals can be picked up by a brain-computer interface and used to control an external device.

Leuthardt’s group worked with several epileptic patients who had neural sensor grids implanted for the purpose of localizing their seizures, providing a unique opportunity for the researchers to monitor cerebral activity. Three patients learned to use neuronal signals associated with same-side movements to control a cursor on a screen and play a video game. Leuthardt hopes to one day develop a prosthetic that uses these signals to improve motor control of a dysfunctional limb—effectively allowing a stroke patient’s one healthy hemisphere to control both sides of his or her body.