London: A peek into the `learning hub` of a songbird`s brain, may help scientists figure out new ways to treat neurological disorders that impair movement like Huntington``s disease and Parkinson`s disease.
To learn its signature melody, the male songbird uses a trial-and-error method to mimic the song of its father, singing the tune over and over again, hundreds of times a day, making slight changes in the pitch of the notes.
For the male Bengalese finch, this rigorous training programme begins around the age of 40 days and is completed about day 90, just as he becomes sexually mature and ready to use his song to woo females.
To accomplish this feat, the songbird`s brain must receive and process large quantities of information about its performance and use that data to precisely control the complex vocal actions that allow it to modify the pitch and pattern of its song.
Now, scientists at UCSF have shown that a key brain structure acts as a learning hub, receiving information from other regions of the brain and figuring out how to use that information to improve its song, even when it``s not directly controlling the action.
Years of research conducted in the lab of Michael Brainard, PhD, an associate professor of physiology at UCSF, has revealed that the adult finches can keep track of slight differences in the individual “syllables,” or notes, they play and hear, and make mental computations that allow them to alter the pitch.
For previous experiments, Brainard and his colleagues developed a training programme that induced adult finches to calibrate their song.
They designed a computer program that could recognize the pitch of every syllable the bird sang.
The computer delivered a sound the birds didn``t like—a kind of white noise—at the very moment they uttered a specific note.
Within a few hours, the finches learned to change the pitch of that syllable to avoid hearing the unpleasant sound.
In their new research, the UCSF neuroscientists used their technology to investigate how the learning process is controlled by the brain.
“It`s the first place where the brain is putting two and two together,” said Jonathan Charlesworth, a recent graduate of UCSF`s neuroscience PhD program and the first author of the new paper.
“If you remove the basal ganglia in a bird that hasn`t yet learned to sing, it will never learn to do so,” he said.
The theory suggests that once a basic, frequently repeated skill such as typing, singing the same song or shooting a basketball from the free-throw line is learned, control of that activity is carried out by the motor pathway, the part of the nervous system that transmits signals from the brain to muscles.
But for the basic routine to change—for a player to shoot from another spot on the basketball court or a bird to sing at a different pitch—the basal ganglia must again get involved, providing feedback that allows learning based on trial and error.
What remained unclear is what made the basal ganglia so “smart” and enabled them to support such detailed trial-and-error learning.
The scientists sought to answer this question by obstructing the output of a key basal ganglia circuit while training male finches to alter their song using the white-noise blasts.
As long as the basal ganglia were kept from sending signals to the motor pathway, the finches didn`t alter their tune or show signs of learning.
But when Brainard`s team stopped blocking the basal ganglia, the finches immediately changed the pitch of their song, with no additional practice.
“It`s as if a golfer went to the driving range and was terrible, hitting the ball into the trees all day and not getting any better.
“Then, at the end of the day, you throw a switch and all of a sudden you`re hitting the fairway like you`re Tiger Woods,” said Charlesworth.
“The surprise here is that the basal ganglia can pay attention, observe what other motor structures are doing and get information even when they aren`t involved in motor control,” Brainard said.
“They covertly learned how to improve skill performance and this explains how they did it,” he added.
These findings revealed that the basal ganglia`s “smartness” is due in large part to the steady flow of information they receive about the commands of other motor structures.
Brainard claimed that the findings also support the idea that problems in the basal ganglia circuit`s ability to receive information and learn from it may help trigger the movement disorders that are symptoms of Huntington`s and Parkinson`s.
The research is reported as an advanced online publication by the journal Nature.