June 4, 2013
Paying Attention To Error Keeps Your Motor Memories Alive
Brett Smith for redOrbit.com - Your Universe Online
A new study by researchers at Johns Hopkins School of Medicine in Baltimore has found that people who can´t see their errors when performing a physical task will lose that skill, not because the brain forgets, but because it has selected an inadequate technique.
The study, which is published in the Journal of Neuroscience, focused on the idea of “motor memories,” or the body´s ability to know the amount of force and direction needed to move limbs accurately from one place to another. For example, professional athletes typically spend hours perfecting their motor memories to be able to perform at such a high level of competition.
According to Reza Shadmehr, a professor in the Department of Biomedical Engineering at Johns Hopkins, scientists have assumed that a decline in physical performance was due to the decay of motor memories in the absence of reinforcement.
However, Shadmehr and his colleague Pavan Vaswani came to a different conclusion after asking volunteers to perform a simple task with a few twists.
In the study, the two researchers instructed the volunteers to move their blue dot avatar toward a red dot being shown on a display screen while their hands were not visible. The research team had also rigged the joystick to pull to the left as the volunteers moved the joystick toward the red dot. Eventually, after practicing for several tries, volunteers were able to move the blue dot straight to and past the red dot by compensating for the leftward pull.
Once the volunteers had mastered the initial task, the two researchers secretly altered the setup. For one group of 24 volunteers, a stiff spring was used to guide the users straight to their target, meanwhile measuring how much rightward force each participant was applying. During this part of the experiment, the volunteers were made to think that they were doing the task perfectly every time. Eventually, they stopped pushing to the right, seemingly "forgetting" learned motor memories.
For another group of 19 volunteers, the researchers added the guide spring, but also altered the feedback on the screen to show reruns of earlier efforts. This caused the participants to be ignorant of any errors they were actually making, including pushing too far to the right. This group continued to do the task as they had learned during the first part of the experiment — repeatedly applying the correct amount of force to the joystick.
The study´s results showed that a decline in performance "isn't just a process of forgetting," Vaswani said. "Your brain notices that you are doing this task perfectly, and you see what you can do differently."
"Our results correct a component of knowledge we thought we understood,” Shadmehr added. “Neuroscientists thought decay was intrinsic to motor memories, but in fact it's not decay – it's selection."
Understanding how motor memories work could be the key to treating victims of stroke or traumatic brain injury. In 2011, USC scientists discovered a mechanism behind the way short- and long-term motor memory coordinate and compete against one another.