When you think about which animals most closely resemble people, naturally thoughts turns to primates, our closest ancestors. But while nonhuman primates shared much neural wiring with people, when it comes to singing, it may surprise you to learn that we take our notes from songbirds. A new study suggests that people and songbirds draw on the same neural structures to imitate sounds.
“The goal of our study was to compare monkey and songbird models of imitation, to see which best describes what the human brain is doing,” says Michel Belyk of the University of Maastricht in the Netherlands. “Once we know which animal are most appropriate to model this aspect of the human brain, we can start to look at them a little more closely.”
As published in the Journal of Cognitive Neuroscience, Belyk (when he was at McMaster University) and his colleagues used fMRI to study brain activation while people either: imitated simple melodies that they had never heard before, simply listened to melodies, or sung familiar melodies from memory. Because MRI machines are so loud, the researchers had to use a technique called “sparse sampling” – involving staggering the data collection with the stimuli while in the scanner – to give people pockets of silence to sing in.
They found that imitation was associated with greater activation in a subset of the corticostriate system, the pathway between the cortex and striatum, called the putamen. This region is analogous to an important region for vocal learning in songbirds.
Belyk spoke with CNS about these findings, his interest in singing, and what the work could mean for people with speech disorders.
CNS: How did you become personally interested in this research area?
Belyk: I am not what you would call a good singer. So, in part I’m studying why I find karaoke so hard. Actually, it turns out that this is fairly common and that although humans are on the short list of animals that can learn to make new sounds with their voices, it still takes a lot of practice.
CNS: How do you define vocal imitation? What do you think makes vocal imitation so special in people?
Belyk: Vocal imitation is the ability to hear a new sound, such as a musical melody or a word, and sing or speak it back. This ability is really quite rare in animals and it’s an important part of how we learn to speak. You have to hear the sound then figure out which combination of muscle movement might make something similar. Despite the common expression “monkey see, monkey do,” it’s quite controversial whether monkeys and non-human apes are really able to imitate. Looking specifically at vocalization it’s clear that they are poor imitators. While children readily imitate the sounds that they hear, “monkey hear” doesn’t become “monkey say.” So, there must be something interesting going on in the human brain to make this happen.
CNS: What have we known previously vocal imitation in people?
Belyk: We often make models of how the human brain works based on what we’ve learned about the brains of other animals. Some researchers have made guesses about how people’s brains do vocal imitation based on what we know from research on chimpanzees. This is appealing because we share relatively recent common ancestry, so the chimpanzee brain has a lot in common with ours. But, like I mentioned, chimpanzees don’t actually imitate the sounds that they hear.
Other researchers have looked to songbirds. Although they aren’t very closely related to humans, songbirds are really good at vocal imitation. In fact, even though the songbird brain is generally very different from the human brain, not just in size but in general layout, the anatomy of the brain system that controls birdsong is remarkably similar to the anatomy of the one that humans use to speak and sing. A big part of the contribution of our research is to bring us closer to understanding how we can use songbirds as models to understand the human brain.
CNS: Why is it important to understand vocal imitation?
Belyk: Human neuroscience comes with a lot of limitations. Aside from really exceptional cases, we generally have to use non-invasive methods like fMRI to study the functioning human brain. Although we can learn a lot using modern non-invasive brain imaging, we’re still operating at a fairly course scale and don’t come near the level of detail that can be achieved with more invasive wet-lab techniques. That’s where having a good animal model comes in. Although researchers have already started using songbirds as a model for the human speech system, we really need to understand what we have in common, and what we don’t. If we can do that, then we’ll be able to learn a lot about how this system can breakdown in humans (resulting in speech disorders) by looking at similar cases in birds, and maybe how to fix it.
One example is stuttering. Despite decades of research we don’t really know why some people stutter and others don’t. There has already been some interest in looking to songbirds as a way to solve the puzzle, and now this is becoming more and more plausible.
CNS: What were your most excited to find?
Belyk: We found that the putamen and a related network of brain areas were more active when people imitated a new melody compared to either just hearing a melody or just singing a familiar tune. This was exciting because this is very similar to what was predicted from songbirds.
CNS: What are the evolutionary implications of the work?
Belyk: This adds to a growing pile of evidence that humans and songbirds may have alighted on similar solutions to the problem of learning our large and complicated vocal repertoires.
CNS: What do you most want people to understand about this research?
Belyk: Humans are bird-brained, and that’s a good thing. We know much more about how songbirds sing than how humans speak, but now we can start to learn more about the human brain by looking at what we already know about the brains of birds.
CNS: What’s next for this work?
Belyk: In the end, we would like to have a complete understanding of how the complicated network of brain areas that controls the human voice communicate with one another to do their job, how a breakdown of this system can contribute to disorders of speech, and maybe inform interventions to help people recover. But of course, that’s a long way off.
-Lisa M.P. Munoz
