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The neuroscience of birdsong

Posted Jun 08 2010 8:34pm
I’ve decided to write a couple of articles on a relatively underappreciated area of neuroscience: the study of birds. I hope to demonstrate that although the term “bird brain” is used as an insult in everyday bicker, the tiny brains of birds are more complex than they are perceived to be. Bird brains may even be able to teach us a thing or two about the brightest of human brains. In this first post, I will describe birdsong – a rare example of music production in nonhumans.

You’ve probably woken up to the high pitch of singing birds before. If you pay close attention and analyze birdsongs, you’ll find that birds are capable of producing quite complex vocal patterns. Some bird species are able to produce over 1000 song syllables! However, the most commonly studied bird in the context of birdsong is the zebra finch, because this bird is simple: it sings just one song type. Male zebra finches sing to attract female mates, whereas female zebra finches don’t sing. The brain circuitry for song control in zebra finches is well characterized.

The most studied region in the schematic above is HVC, at the top of the bird brain. A bird with a damaged HVC cannot sing, and studies on the functional role of HVC have confirmed that it is a critical area for song production/control. In zebra finches, the HVC is much larger in males who sing than in females who don’t sing.

When male zebra finches sense the presence of a female, neural signals converge at HVC, causing the male to sing. The green pathway from HVC to RA ends at the syrinx, a vocal organ situated at the top of the trachea. The green pathway must be intact for birds to properly control muscles that modulate complex sounds being produced. The other main pathway is the red one that goes from HVC to Area X. The red pathway is involved in learning songs from “tutor” birds and receiving self-feedback while singing (so birds can correct themselves when they make mistakes).

An interesting area of study is the comparison of birdsong to human language. The hypothesis that the two are analogous is rejected by critics who maintain that birdsong is a single memorized set of vocalizations, whereas language involves a set of rules that can be combined in infinite unique ways. Nevertheless, birdsong and language parallel one another in important ways. When they are learning how to sing, birds display vocalizations that are similar to human infant babbling. Furthermore, the gene FoxP2 that is involved in neural control of vocal development is active in human and zebra finch brains in strikingly similar ways. This gene is also found in other animals such as mice, but it is best to study the gene in birds because their vocal behaviours are closest to ours.

So in summary, we now know a lot about the neural substrates of birdsong, and bird vocalizations can be looked at as both a behavioural and biological model of human language development and/or dysfunction. This post was intended to be a quick summary of what’s most interesting about the study of birdsong, so keep in mind that I’ve only scratched the surface of the topic.  Perhaps the next step will be determining how birds can dance...



References:

Brenowitz EA, Margoliash D, & Nordeen KW (1997). An introduction to birdsong and the avian song system. Journal of neurobiology, 33 (5), 495-500 PMID: 9369455

Brenowitz EA, & Beecher MD (2005). Song learning in birds: diversity and plasticity, opportunities and challenges. Trends in neurosciences, 28 (3), 127-32 PMID: 15749165

MacDougall-Shackleton SA, & Ball GF (1999). Comparative studies of sex differences in the song-control system of songbirds. Trends in neurosciences, 22 (10), 432-6 PMID: 10481186

Teramitsu I, Kudo LC, London SE, Geschwind DH, & White SA (2004). Parallel FoxP1 and FoxP2 expression in songbird and human brain predicts functional interaction. The Journal of neuroscience : the official journal of the Society for Neuroscience, 24 (13), 3152-63 PMID: 15056695
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