Male songbirds learn their songs by a process of trial and error, singing over and over while making subtle corrections. The male Bengalese finch begins this process at around 40 days old, and finishes around day 90, just as it reaches sexual maturity.
To accomplish this, the bird must receive and critically process large amounts of information, then adjust its pitch and melodic patterns.
For the first time, researchers have shown that a key brain region acts as a learning hub, receiving information and reprocessing it, even while it isn’t doing the action.
The researchers think that their findings will help them figure out new ways to treat neurological disorders that impair movement, such as Huntington’s disease and Parkinson’s disease.
This previous research was done by using a computer program to track the notes the finches play, and then play a sound the birds didn’t like at the same time the finch was singing a note. Within a few hours, they learned how to sing a note that would allow them to avoid hearing the sound that they didn’t like.
In the new study, the researchers investigated how these learning processes occurred in the brain. The prevailing theory is that it is controlled by a brain structure called the basal ganglia, a structure that is involved in motor control and learning.
“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.”
According to popular theory, once something is learned, it is carried out by the motor pathways in the nervous system. But for changes to be made to learn a skill, the basal ganglia must get involved, giving the feedback that allows those changes to be made.
What the researchers were unsure of is why the basal ganglia is able to do that. Is it receiving information from other parts of the brain?
To find out, the researchers blocked the output of an important basal ganglia circuit while training the songbirds to alter their songs to avoid the sounds that they didn’t like.
While the signal to the basal ganglia was being blocked, the birds didn’t change anything, and didn’t appear to be learning at all. But as soon as they stopped blocking the signal, the birds immediately changed their pitch in the appropriate way, without anymore 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,” said Charlesworth. “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.”
“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.”
The study suggests that the ‘intelligence’ of the basal ganglia is from the constant flow of information it receives from other motor structures, supporting the idea that problems in the basal ganglia are responsible for the movement problems that occur from Parkinson’s disease and Huntington’s disease.