Unexpected external stimulus, such as a sound or visual cue, can act as an alarm for the brain to detect a dangerous situation, according to a study that has implications for Parkinson’s disease.
These sensory triggers were found to promote an inhibitory signal from the brain to quickly stop muscles from reacting, providing new insights on how the brain and muscles interact to control movement.
The University of Iowa researchers studied how people stopped an action. They found that when participants heard an unexpected sound, they stopped an action more often than when they heard no sound at all.
These findings may help researchers understand how to enhance brain-muscle communication as a strategy to treat patients with motor-control disorders, such as Parkinson’s disease and attention deficit hyperactivity disorder (ADHD).
Sixteen healthy volunteers had to perform a simple Go or No Go task and were either exposed or not to warning sounds. During the experiments, brain activity was measured, as well as muscle response.
Researchers observed that when participants were exposed to unexpected warning signals, they would stop their action more often than when they heard no sound at all (80% vs 65%).
This improved stopping action response was found to be accompanied by increased brain activity that was associated with increased stop signals sent to the muscles.
A similar inhibitory response was also reported when participants were trained to expect the warning sounds. Even though they were expecting the warning sound, the brain still responded in a protective way by blocking their action.
“It seems like the brain’s communication with the motor system is so hard-wired, and this ability to stop an action is so innate, that even repeated practice won’t really alter it,” Jan Wessel, assistant professor in the department of psychological and brain sciences at UI and senior author of the study, said in a university press release. “Therefore, finding other avenues to trigger the brain’s rapid stopping and improve stopping outcomes could be of great potential.”
This type of inhibitory response is not limited to sounds but to any unexpected event, Wessel said. “The hypothesis is that an unexpected visual event, or an unexpected vibration on your skin, would have the same effect. It’s just the fact that something happened that was unanticipated,” he added.
Experimental data revealed that the communication between the brain and the motor system is almost instantaneous, happening in fractions of a second. “Our brain has evolved to do this. The human brain is adapted for survival, and I think that’s why these systems are hard-wired with one another,” Wessel said.
Collectively, these findings suggest that the brain and the muscles are tightly linked to manage surprise response and movement control. This opens new research options for reactive motor control in situations of impaired response, the researchers said.
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