February 19, 2013

Prof. Jesse Goldberg Uses Songbirds to Study Learning

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Male zebra finches are born babbling: randomly chattering with no pattern to their singing. As they grow older, their chirps coalesce into a highly regular, repetitive song that is almost identical to that of their father. Prof. Jesse Goldberg, neurobiology and behavior, studies the learning process that is responsible for this behavior in songbirds in order to better understand how motor learning occurs in humans.

Goldberg uses the zebra finch as his model system because mammalian and songbird brains are similar. Both contain a collection of neurons in the brain called the basal ganglia, which controls trial-and-error learning and motor behavior.

As a medical student, Goldberg gained experience with patients diagnosed with diseases such as Parkinson’s, which affects both cognitive and motor behavior and originates from a malfunction in the basal ganglia. Seeing how damage to one part of the brain could affect both cognition and motion sparked Goldberg’s interest in the relationship between motor control and learning.

“The reason we don’t understand the connection in humans is because it’s insanely complicated. We need to go to a system where we think we might be able to understand it,” Goldberg said.

He said the zebra finch provides a simpler means of studying trial-and-error motor learning.

“There is discrete, specialized pathway in the zebra finch brain, a collection of interconnected nerve cells that is similar to the electrical circuit that turns on a lightbulb,” Goldberg said.

This brain circuit responsible for zebra finch song learning involves the basal ganglia, he said.

In order to study vocal babbling and song learning trajectories, Goldberg records juvenile birds singing and graphs the frequencies of their songs in charts called spectrograms. These spectrograms allow him to see the evolution of a juvenile song to an adult one.

Goldberg then probes into the learning mechanism by measuring the neural activity of individual neurons in the basal ganglia via electrodes implanted in the birds’ brains. According to Goldberg, there are more than one million neurons in the songbird’s learning pathway, but there are far fewer distinct neuron types. By repeatedly measuring the firing of specific classes of neurons, Goldberg can identify which neuron types are important to learning behavior.

Once he narrows down which types of neurons play key roles in generating vocal babbling, Goldberg tests his hypotheses using optogenetics. Optogenetics involves genetically engineering certain cell types in the brain to be sensitive to light by introducing viral DNA that codes for light sensitivity.

The technique’s main strength is that it allows researchers to stimulate only specific neurons using light. Drugs or stimulating electrodes, which activate or inhibit large areas of the brain, do not exhibit the same resolution.

According to Goldberg, the trial-and-error process that relates to song learning in baby male zebra finches is the same as the trial-and error process behind motor control in humans.

“Virtually all human motor behaviors are learned through trial-and-error, a process by which the brain generates exploratory action through the motor system,” Goldberg said.According to Goldberg, in the trial phase of trial-and-error learning, humans experiment with a variety of motor behaviors. He provided the example of a beginning tennis player hitting tennis balls inconsistently at first while exploring different methods of holding and swinging the racket.

The next step of motor learning, the error phase, involves evaluating successes and failures. The tennis rookie decides if an action was good or bad.

Did a particular grip on the racket aid in the goal of getting the ball over the net? Whether or not the motor action was helpful dictates whether it should be repeated. This process of learning helps refine motor control in humans.

Last semester, Goldberg taught a course called “Neural Circuits for Motor Control in Health and Disease,” and this semester he is a guest lecturer in “Introduction to Neuroscience.”

Goldberg advises students not to take rejections too harshly.

“Failures are important to go through, and are a totally normal part of any learning process. If we just go back to trial-and-error learning, the whole point of it is realizing that you did something wrong. Don’t take it personally,” Goldberg said.

Original Author: Jacqueline Carozza