Singing in the Brain: Bird Neuroscience

Posted by Drew Schreiner on March 25, 2021 in Animals, Behavioral Neuroscience, learning, Neuroscience | Leave a comment

Many of us have adopted new hobbies or interests in this strange quarantine world. For me, I’ve started to really appreciate birds. Birds and birdsong are almost omnipresent and for those of us living in more developed areas, they are oftentimes one of our only real reminders of and connections to the natural world. So, I’ve learned to identify some of my local birds and their songs, and I’ve even slowly befriended a mated pair of crows (Sheryl and Russel Crow). But aside from this personal interest of mine, birds are absolutely fascinating from a neuroscientific point of view.

Learning to sing

Imagine a baby human learning how to speak. First she listens to her parents, slowly picking out the acoustical features of simple words like “dad” or “mom”. Eventually, she starts to babble, explores how to control her vocal muscles in order to make sounds, and how to imitate the sounds and words she has heard before, until eventually she is able to say “dada.” Remarkably, this process also occurs in many species of birds. First a chick listens to their father’s song, next they “babble” as they figure out how to control their vocal muscles, and finally, through many repetitions they refine their song across adolescence until it “crystallizes” into the adult song. 

But it turns out that this ability, known as vocal learning, is incredibly rare in the animal kingdom. Among mammals, only us humans, bats, and some marine mammals are known to “do” vocal learning. Notably absent from this list are our closest relatives: non-human primates. What this means is that birds are a great model organism for understanding how humans learn to speak.

How does the brain control vocal learning? First, it’s important to distinguish between vocal learning and just any sort of vocalizations. Many animals have innate (meaning, no learning required) vocalizations – think of a dog’s bark. Even animals that undergo vocal learning also generally have innate vocalizations too (a human baby’s cries, a bird’s alarm call when they see a predator). A seminal study in canaries was the first to pinpoint several key brain regions necessary for birdsong, but didn’t really investigate this key distinction [1]. Subsequent studies have revealed several more nodes in this song circuit (see Figure 1 to the right), and have also helped to reveal a lot of interesting insight into exactly how each brain region contributes. While some regions are important for singing/vocalizations in general (such as HVC from Fig. 1 here), others (such as LMAN) seem to be particularly important during vocal learning. For instance, while lesions of LMAN in juvenile birds impair the development of birdsong, the same lesions carried out in adulthood after the birds learned their song had no effect [2].

While much is known about the role each of these little brain regions plays, there remain many open questions. As an example, while some birds like the Zebra Finch (the featured image) learn a single song as a juvenile, other birds learn several songs during the same period, and still others can continue to learn songs throughout their life instead of only as a juvenile. Perhaps the most obvious examples are parrots, which can even be taught human speech. Much less is known about how vocal learning continues in adult birds. Similarly, we don’t know as much about singing and vocal learning in female birds, as neuroscience research has primarily focused on songbird species where only the male sings to defend territory and attract a mate. Especially remarkable is that despite having drastically different vocal anatomy (birds have a syrinx instead of a larynx), they are able to explore, experiment, babble, and improvise in such a way as to replicate our speech.

Bird brains and mammal brains

What’s more, aside from having different vocal anatomy, birds also have totally different brains than mammals. Birds don’t even have a cerebral cortex, the brain region that is generally thought to give primates some of our more impressive cognitive abilities. And yet, despite lacking a cortex, birds are able to do many cognitively demanding tasks. As already mentioned, they are among the rare vocal learners in the animal kingdom, and some parrots – like the famous African Grey “Alex” seem to have semantic understanding of what words mean or refer to [3]. Even aside from vocal learning, some species of birds are intelligent in different ways. New Caledonian Crows are famous for their use of tools in the wild. Amazingly, in the lab they can learn even more complex tasks (check out this crow which understands the concept of water displacement). In fact, these crows rival non-human primates in their ability to use tools on other tools to acquire food in what’s known as “meta tool use” [4].

While it may at first seem counterintuitive to study vocal learning or intelligence in birds (with their vastly different brains) in order to better understand humans, it actually opens the door for a whole bunch of interesting questions. The comparative approach can be extremely useful. While bird brains may appear physically different, lacking many of the structures or organization of mammalian brains, there might also be important similarities. Indeed, it seems likely that bird brains would have to perform many similar tasks and computations as mammalian brains (a fact long ago noted by Harvey Karten, see this Neuwrite post for an excellent interview). 

How do birds perform the same tasks as other animals using totally different machinery? There is tremendous potential here to reveal fundamental mechanisms or computations in the brain (see this Neuwrite post on the comparative approach of neuroethology). While the bird brain lacks the traditional layered structure of the mammalian cortex, a recent study found that there are nevertheless some striking similarities at the molecular and cellular level (for example, neurons with similar gene expression and connectivity patterns as those in distinct layers in the mammal) [5]. Further studies in this realm might help us better understand general principles of how the brain works aside from superficial differences in structure. 

Flowing in through my open window I can hear the trilling call of a Dark-Eyed Junco. Out on the balcony, the hummingbird feeder is busy with an evening rush of Anna’s Hummingbirds. Birds and birdsong are beautiful, the muse of poets and songwriters for millenia. Some say that science can “ruin the mystery” of nature, that our incessant drive to understand renders the world less magical. For myself, every little detail, every new piece of knowledge gained just fills me with more wonder. The array of evolutionary, genetic, molecular, developmental, and behavioral factors that all have had to come together and work just right in order for me to hear that little Junco’s song is incredible. We have so much to learn, but now that we understand just a bit of what makes birds tick – and sing and think – the world just seems a bit more musical.

References

1. Nottebohm, F., Stokes, T. M., & Leonard, C. M. (1976). Central control of song in the canary, Serinus canarius. Journal of Comparative Neurology, 165(4), 457–486. https://doi.org/10.1002/cne.901650405
2. Bottjer, S. W., Miesner, E. A., & Arnold, A. P. (1984). Forebrain lesions disrupt development but not maintenance of song in passerine birds. Science, 224(4651), 901–903. https://doi.org/10.1126/science.6719123
3. Pepperberg IM (1999) The Alex studies: cognitive and communicative abilities of grey parrots. Harvard University Press, Cambridge
4. Taylor, A. H., Hunt, G. R., Holzhaider, J. C., & Gray, R. D. (2007). Spontaneous Metatool Use by New Caledonian Crows. Current Biology, 17(17), 1504–1507. https://doi.org/10.1016/j.cub.2007.07.057
5. Colquitt, B. M., Merullo, D. P., Konopka, G., Roberts, T. F., & Brainard, M. S. (2021). Cellular transcriptomics reveals evolutionary identities of songbird vocal circuits. Science, 371(6530). https://doi.org/10.1126/science.abd9704

Images:

Featured Image: https://news.mit.edu/2015/neural-patterns-for-birdsongs-1130

Figure 1 via paper [5].

Figure 2 via: http://people.eku.edu/ritchisong/birdbrain.html

Junco: Photo by Jack Bulmer on Pexels.com