Sound-reward
connection changes brain
by Toni Baker
If you’ve ever wondered how you recognize your mother’s voice without seeing her face or how you discern your cell phone’s ring in a crowded room, researchers may have a piece of the answer.
Their work indicates associations with positive sounds cause significant changes in the sensory cortex, the part of the brain that responds to sound.
“When something starts to predict a good outcome, the sensory part of the brain that responds to those events starts to respond more strongly, making it easier for the brain to cause a behavioral response,” says Dr. David T. Blake, MCG neuroscientist and lead author on a study in the Oct. 19 issue of Neuron.
By monitoring the action potentials of about a dozen key neurons in monkeys, researchers found neuronal responsiveness increases dramatically after just a few training sessions.
These neuronal fireworks were short-lived, replaced by brain rewiring that shows the animal has learned, Dr. Blake says. In the few monkeys that initially didn’t make the connection that a change in pitch in a series of sounds meant they were getting a reward, no brain changes occurred.
“The same processes happen to people as we learn, especially in the area of sensory discrimination,” Dr. Blake says. “We learn how to tell people’s faces apart, we learn how to distinguish different words, we can identify different speakers by the tenor and tone of their voice. We are studying how the brain changes as part of sensory discrimination learning.”
The findings have wide implications for learning, including improved treatment for language impairments. California-based Scientific Learning, a neuroscience company that grew out of the University of California, San Francisco, already is using advances in behavioral science to develop computer programs that dramatically improve the reading skills of dyslexic children. Another San Francisco-based neuroscience company, Posit Science, is exploring its potential in age-related cognitive decline.
In work published in 2002 in the Proceedings of the National Academy of Sciences, Dr. Blake first taught monkeys that when they leaned forward to break an infrared beam, a series of sounds would begin. “If they leaned back after a change in the sound series, they got a reward,” he says. “When they do this, the response of their neurons to those sounds triples in the first two days after they learn that very simple behavior.”
The new study indicates the monkeys just have to make the connection between the sound change and reward for brain changes to occur and that at least some of them don’t have to move a muscle to make that happen.
“It’s an important computational point because there is a lot of interest right now in the brain’s ability to backtrack in time from rewards to find out the earliest thing that predicts that reward. When the monkey identifies the sound change as the cue it’s supposed to respond to to get rewarded, learning and brain changes happen.”