From The Scientist…
When you move only your right arm, there’s neural activity in both the left and right sides of the brain, researchers report today (October 8) in The Journal of Neuroscience.
Recent animal and human studies have hinted that moving muscle on only one side of the body resulted in neural activity from the same side—or ipsilateral—part of the brain. But the data haven’t been convincing enough to completely erase the idea that only the left side of the brain is responsible for movement on the right side of the body or vice versa. The new study shows the ipsilateral brain activity encodes detailed arm movement information including position, speed, and velocity. The results could one day be used to help improve recovery therapies for patients with brain injuries.
“This is an important contribution to our understanding of how the brain controls arm movement because it reveals a greater role of ipsilateral brain activity than previously recognized,” writes Nathan Crone, a professor of neurology who runs a cognitive neurophysiology lab at Johns Hopkins University in Maryland and was not involved in the research, in an email to The Scientist.
In the study, Eric Leuthardt, professor of neurosurgery, engineering, and neuroscience at Washington University in St. Louis, and his colleagues enlisted four patients with epilepsy who were to undergo surgery and who had electrodes implanted for a week under the skull. The electrodes were placed directly onto the cortex of the patients’ brain cortex regions, including the primary motor cortex—responsible for coordinating voluntary muscle movements. The patients volunteered to perform three-dimensional, individual arm motions while the researchers recorded neural activity from the implanted electrodes. The team then used machine learning to derive speed, velocity, and position information on each movement—gathering data on fine motor movements that cannot be easily captured using noninvasive techniques such as functional magnetic resonance imaging (fMRI).
Based on previous study results, Leuthardt and his colleagues hypothesized that the neural activity from a single arm movement would differ in the right and left hemispheres. But, when the researchers compared the neural activity recorded in the left hemisphere for right arm movements and then left arm movements, the two patterns were very similar. They weren’t identical, but the brain activity in a single hemisphere could predict the movements of both arms, not just the arm on the opposite side. “What was surprising was how similar the [neural] encoding on the same side of the brain [was to] that on the opposite side of the brain,” says study coauthor David Bundy, now a postdoctoral fellow at the University of Kansas Medical Center.