How do songbirds learn to sing?
Once birds make it out of the nest, songbirds have to set about learning their songs. Some birds, like parrots, are called “open-ended learners” because they can continue learning more and more sounds over their lifetimes. But others, on the other hand, have only a specific period of teenagerhood where they learn their songs, and zebra finches are an example of this. Mimi Kao, at Tufts University, studies how this happens, and spoke with Chris Smith...
Mimi - Well, vocal learning in songbirds shares many similarities with vocal learning in humans, and it occurs in two phases. In the initial sensory phase of learning, birds are just listening, and they're forming an auditory memory of an adult tutor. And then in a second phase, known as sensory motor learning, they begin to practice. And the sounds that they make first are quite variable, much like the babbling in human infants, but they're listening to themselves as they're singing and they're trying to correct it. And so they continue practicing thousands of times a day until they're able to make an accurate copy of the tutor song.
Chris - Why teenagerhood, why don't they do that from the get-go?
Mimi - Well, initially the areas of the brain that are important for producing songs are not totally wired up. So the connections aren't there yet. The auditory areas are there and functioning, so they're listening, but around 25 or 30 days those connections from the song motor region form the connections with the next region and the birds begin to vocalise.
Chris - Interesting that it's the adolescent period of their life, and we're very familiar with human adolescents, especially if they're male, doing all kinds of extraordinary extravagant things to try to get the attention of the opposite sex. So you've sent us a couple of clips of what happens with the birds you've been studying. First of all, we're going to hear the sound of a male just singing.
Mimi - Well, you'll hear a short clip where the male sings a couple of repetitions of his song. And he knows how to sing it, but sometimes it's a little variable and he might also vary the timing, so there might be some pauses.
Chris - And we're going to contrast that with what happens when you introduce a female into the mix, so the male's aware that there's a female there.
Mimi - Yeah, so we think of this as a high intensity performance song. He sings faster, he sings more of the repeats. It's just a higher song rate.
Chris - But this is like, you know, doing extra flips on your skateboards, trying to get the girls interested.
Mimi - Definitely! The male is trying to get the female's attention and he's singing his best version of song. And even though we can't hear it, the female can hear subtle differences between when the male is practicing and when he's performing. And it turns out that the performance song is much more stereotyped from one trial to the next.
Chris - You mentioned earlier about how the brain wires itself up and then reaches this point at which it's optimally wired in order to start being able to acquire songs and then memorise them. Do we now understand though, which bits of the brain are doing that?
Mimi - There are two or three parts of the brain that are involved in this. Song motor areas that are producing the sound, auditory areas that are used for evaluating the performance of the song, and then there's a cortical basal ganglia circuit that we know is important for learning the song and for being able to change it from moment to moment, but also over the course of learning.
Chris - Are they the same bits of the brain that I'm physically using to talk to you?
Mimi - Yes, there are many similarities. Basal ganglia circuits are found in all vertebrates and they're important for motor learning and for motor performance in all vertebrates. And one thing that makes songbirds special is that, like humans, there are connections from the cortex to those motor neurons that then project to the parts of the body for producing the sound.
Chris - And does that mean if you know which bits of the brain are doing this, you can actually potentially manipulate it and thereby prove that that's how the birds are doing what they're doing?
Mimi - Yes. There've been a number of studies to manipulate either those motor areas that are responsible for producing the song or this cortical basal ganglia circuit that's important for learning and for changing the song.
Chris - And can you therefore physically change how a bird sings? If you were to go in and fiddle with those brain areas, would the song change?
Mimi - Yeah so for example, we can put in certain drugs into the brain to change the level of activity in that part of the brain. And if we do this in the cortical basal ganglia circuit and we activate it, so we cause it to fire more and to send signals at a higher rate, then we can drive changes in the song and cause the bird to change the performance of individual syllables, for example, altering the pitch. We can also change the sequence of the song. And most recently we've shown that we can cause birds to stutter so that they'll repeat certain elements of their song a small number of times before moving on to the next syllable.