Parallels between song and speech
What the zebra finch can tell us about ourselves
‘This is it!’ says Sanne Moorman. ‘The zebra finch’s glorious song.’
Her computer speakers are playing a twittering sound. It’s not unpleasant, but a little repetitive. It’s not all that special, really. Moorman chuckles: ‘Very few people actually like it.’
But to the biologist and auditory learning expert’s ears, it’s heavenly. ‘Zebra finches can decide on their own that they want to learn a new song. When they do, they’re incredibly motivated. They practise the song five hundred to a thousand times a day, just all the time. That’s fascinating to me.’
There is a lot of information Moorman can gather from the tune a finch might sing. One thing she listens for is whether a finch sings differently from its father, or which different sounds it uses in its song. In the end, though, it’s not really about the finches’ songs. She hopes these birds can help her figure out something else entirely: how children learn how to speak.
Vocal learners
It may sound weird, since there’s such a big difference between people and birds. But according to Moorman, there are a lot of similarities in the ways children learn how to speak and how zebra finches learn their songs.
Zebra finches are incredibly motivated, that’s fascinating to me
Both people and songbirds are vocal learners. That means they don’t know how to speak or sing on their own. While a dog will start barking without ever having heard another dog do it, children don’t learn how to speak and birds don’t learn how to sing without first hearing an example.
This means birds are ideal candidates for a study on language acquisition. Zebra finches are used the most, says Moorman, since other animals that learn vocally, such as dolphins or whales, are more difficult to keep in a laboratory setting.
Same function
She also says that the brains of human beings and songbirds don’t differ as much as you might think. Large parts of the brains of songbirds develop the exact same way as those of people as they grow up. And while other areas develop differently, they do work the same; serving the same function when it comes to producing or understanding sound, speech, and song.
‘Zebra finches can help us to study things about speech acquisition that we don’t yet know about children’, says Moorman. ‘There are certain processes happening in the brains of children that have to do with speech acquisition, but we don’t exactly know why or how they work.’
We don’t exactly know how certain processes in the brains of children even work
This type of research also adds to the fundamental knowledge of what happens in the brain when people try to learn or remember things. Songbirds are perfect, because we know exactly which areas in the brain are responsible for the learning process. And while other species have multifunctional brain areas, it appears that songbirds possess an area that’s dedicated to a single, clear goal: producing precise songs.
‘Manipulating those areas, for instance by inhibiting it with a laser, will only affect a bird’s singing’, says Moorman. ‘But in other species, it will also affect other movements.’
Brain activity
Moorman has been studying zebra finches for years. She’s compared the right and left hemispheres of young zebra finches as they listen to the song sung by their tutor – often their father. She found out that young finches are better at copying their tutor when their left hemisphere works harder than the right one. Once the zebra finches reach maturity, both hemispheres show the same amount of activity. From this, she concluded that a more active left hemisphere could be particularly important to the learning process.
She also manipulated brain activity in adult zebra finches. Brain cells tend to activate for just a little while, resting before activating again. By injecting a substance that removed that block, allowing the cell to activate almost immediately, Moorman considerably shortened that rest period. ‘Normally, adult zebra finches sing the same song their entire lives, but now, they started changing all sorts of things about their singing.’
It’s likely that the shorter rest in brain activity had a great impact on the young birds. ‘When young birds are learning their song, they practise all the time. They have to try out all these different songs to see which one resembles the example the most. My colleagues and I think that re-activating the cell so much more quickly is the reason the young birds can try out so many different songs.’
Speech disorder
Moorman wants to study what changes in the brains of young zebra finches while they’re learning an older bird’s song and whether those changes continue over time or stabilise. She expects this will give her a better idea of the fundamental function of memory in vocal learning.
The birds started changing all sorts of things about their singing
‘Approximately 7.5 percent of children have a speech disorder that we don’t know the cause of’, she says. ‘This research might help us figure out what goes wrong in these disorders, and perhaps we can even solve them one day.’
She will also be teaming up with linguist Defne Abur to see if the songbirds can function as a model for patients with Parkinson’s. ‘Parkinson’s patients often have trouble speaking’, she says. ‘We think birds might just be the solution to that.’
The area in the brain that doesn’t work as well in people with Parkinson’s, the basal ganglia, serves an important function in zebra finches learning their song. While we can’t study this area in human beings, we can in zebra finches.
‘We want to find out if there are any parallels between people with Parkinson’s and zebra finches. If there are, we’ll first try to solve the issue in zebra finches and then we’ll see if that works for Parkinson’s patients as well’, says Moorman. ‘Eventually, we hope to come up with therapies for Parkinson’s and other speech disorders.’