How birds know what not to tweet
The chemical dopamine dips when a bird’s tongue trips
Adult zebra finches twitter one short sequence of notes flawlessly, over and over. How do they perfect their signature tweets? A chemical signal in the brain dips when they make mistakes, a new study shows. And that same signal spikes when they get it right. These results aren’t just for the birds, though. They might help scientists also understand how people learn to play music, shoot free throws and even speak.
A bird learning to sing has a lot in common with a baby learning to talk, says Jesse Goldberg. He’s a neuroscientist — someone who studies the brain — at Cornell University in Ithaca, N.Y. Baby zebra finches hear songs from a tutor — usually their father — when they are chicks. They then grow up to sing dad’s song. But like a toddler learning to talk, a baby bird starts off by babbling. It sings cascades of different notes that don’t make a lot of sense. As it gets older, Goldberg says, “gradually the babble becomes a copy of the song.”
How does the growing finch perfect its pitches? It has to compare what it’s singing to the memory of its tutor’s performance. Goldberg and his colleagues suspected that brain cells producing dopamine (DOAP-uh-meen) might help birds make this comparison. Dopamine is a neurotransmitter — a chemical that transmits messages in the brain. It moves a signal from one nerve cell in the brain to another.
Different neurotransmitters play different roles. Rewards trigger the brain to make dopamine. It, in turn, encourages an animal to change its behavior. This chemical also is important in reinforcement — encouraging an animal to perform some action again and again. In people, dopamine signals will spike when people eat tasty foods, quench their thirsts or take addictive drugs.
Goldberg thought that dopamine might help zebra finches know when they sang their songs right — and when they mis-tweeted. “You know if you make a mistake. You have an internal sense of if you did a good job or not,” he says. “We wanted to know if the dopamine system that people think of as a reward system also plays a role.”
Goldberg and his group started by placing zebra finches in special chambers. The chambers held microphones and speakers. As the finches sang, computers recorded the sound from the microphones and played it back to the birds in real time. At first, it just sounded to the finches like they were singing normally.
But sometimes, the computers didn’t play the birds’ pitches perfectly. Instead, the computers would mess up one note. Suddenly, the finch would hear itself singing the song wrong.
While the birds were singing — and listening to themselves apparently screw up — the scientists observed their brain cells. The researchers had inserted tiny recording wires into the birds’ brains. That let them measure the activity of the finches’ dopamine-making cells. Implanting a tiny electrode into a small bird is no easy feat. “It’s a little bit like trying to balance a needle on a grain of sand in a bowl of shaking Jell-O,” says Richard Mooney. He’s a neuroscientist at Duke University in Durham, N.C., who was not involved in the study.
When the birds heard themselves sing a song spot-on, the activity of their dopamine-making cells surged a tiny bit. But when the finches heard themselves sing a wrong note, there was a large dip in dopamine — a sign to stop the music. Goldberg and his group published their work in the Dec. 9, 2016 issue of Science.
Is pitch-perfect song its own reward?
There’s a dopamine zing when birds sing the right thing. It looks a lot like what happens when other animals, such as rats or monkeys, expect rewards. When these animals are expecting a reward of juice and get it, their dopamine-making cells spike in activity. But when no juice arrives, they experience a dopamine dip — like what happens when the birds hear themselves sing a wrong note.
The difference is that singing isn’t a reward — no matter how much we may enjoy belting away in the shower. This might mean evolution has used the dopamine system in birds — and in other animals — to help judge whether an action is correct or not. That’s Goldberg’s hypothesis.
“I think [the study is] fantastic,” says Samuel Sober. He’s a neuroscientist at Emory University in Atlanta, Ga. He was not involved in the study. But he does note that perhaps, to a finch, singing right could be a reward. The dopamine spikes and dips signal when the bird gets the song right or wrong. He says: “Whether the bird interprets that as punishment or reward is something we have to figure out.”
This dopamine spike could also help scientists understand how people learn, notes Mooney. “It’s the kernel of a wide range of types of motor learning,” or how we learn to perform physical actions, he says. Whether it’s a musical performance or perfecting a jump shot in basketball, “you try again and again. And over time your motor system learns to produce optimal performance,” Mooney says.
As people learn, their dopamine may act as the finches’ did to let them know whether they got it right. The frustration of making mistakes, Mooney notes, “is a small price to pay for lifelong ability.” That’s true whether it’s a finch singing, or your own attempts to play pitch perfect.