On the third floor of the Bryan Research Building, the caged birds do not sing for mating purposes alone.
Richard Mooney, George Barth Geller professor of neurobiology at the Duke Institute for Brain Sciences, and his team of researchers explored the human learning process by observing how male zebra finches learn courtship songs. Prior to the study, published in the September issue of Nature Neuroscience, the conventional scientific viewpoint was that people use the sensory regions of their brains when learning to perform actions and use the motor regions of their brains when actually performing those actions.
The two-and-a-half-year study found, however, that the motor regions of the brain are necessary during the initial stages of learning as well.
“When someone is learning to shoot a free throw they might watch someone really good doing it and try and emulate that,” Mooney said. “But it’s possible, based on these findings, that regions of the brain that have more of a motor function are involved in learning about what to do before commanding the motor system to do it.”
Because the finches were unable to learn a mating song when the motor regions of their brains were inhibited, the findings indicate that there is a greater interplay between the sensory and motor regions of the brain when learning to perform an action.
“It really boils down to the traditional view that there are sensory and motor regions in the brain and that they talk to each other, but that sensory experience affects sensory regions and very slowly guides the motor part of the brain,” he said. “What we found was the complete opposite in that the motor regions in the brain are necessary to sensory learning.”
Mooney likened the way scientists traditionally viewed learning to Rene Descartes’ breakdown on sensory and motor interactions—a person steps on a flame, nerves travel up from the foot to the brain and the brain commands the foot to move. This is not how the mind actually learns to perform functions, though. Instead, the sensory and motor regions of the brain work together, rather than sequentially, to learn processes, the study found.
Finches and the human brain
Zebra finches were used in the study because they are one of the few well-documented examples of animals that exhibit similar learning patterns to humans. They observe or hear an action and then try to perform said action, Mooney said. The finches learn mating songs by listening to a tutor bird perform the song and then trying to perform it back.
Finches were also good candidates because a region of their brain, known as the HVC, is similar to the Broca and Wernicke areas of the human brain, which are responsible for understanding and producing speech, said Todd Roberts, postdoctoral associate in neurobiology and lead author of the study.
The scientists tested whether the birds could still learn a mating song when the HVC, the motor region of the finches’ brains, was disrupted.
Prior to the study, it was thought that disrupting neural activity in a motor area of the brain would not affect birds’ ability to learn a song, Mooney said. Blocking neural activity in the HVC, however, prevented birds from learning the mating song, showing how motor areas of the brain play a role in the learning process.
“This is the first experiment in any animal that we know of where we are using natural interactions to disrupt learning in order to figure out what parts of the brain are important for learning,” Roberts said. “People have been trying to dissect this for a while, but the problem has been, ‘How do we disrupt neural activity in a way where we don’t hinder the pupil in its natural setting?’”
“New buzz word”
In order to better understand the birds’ learning process, the researchers used a relatively new method, called optogenetics, to control the birds’ brain patterns. Implementing this technique, developed in 2005, the scientists used a non-pathogenic virus to insert a light-sensitive gene from another organism into the birds’ brains, where the gene was expressed. In this case, the gene was taken from green algae in the Red Sea. It causes the algae to swim whenever they encounter light.
“The new buzz word is optogenetics,” Mooney said. “We used this novel method— which is probably going to generate a Nobel Prize for the people who produced it within the next decade—to understand neural activity.”
Scientists introduced the light-sensitive gene into the pupil bird’s HVC. Then, wires hooked up to the HVC shone a light when the tutor bird was singing, in order to disrupt the pupil bird’s neural activity during this critical learning period.
“The idea is when the bird is listening to the tutor we are superimposing that region of the brain and scrambling the neural activity that the bird needs in order to learn,” Roberts said.
Graduate student Malavika Murugan implemented the optogenetics in the experiment. Relatively new to the field of neuroscience, optogenetics had been used in rats before, but never in birds. Murugan had to test ways to properly inject the light sensitive gene into the bird, which required using a “gutted,” non-pathogenic virus as a carrier.
Because the HVC and Broca area are so similar, the findings allow for greater understanding of the human mind, Roberts said, adding that understanding how a mind learns and processes information will help understand neural developmental disorders.
“It’s hard to understand what areas of the brain are affected by these disorders, but this study allows us to see what areas of the brain might be partially impacted by neural developmental disorders,” he said.