October 1, 2019
Written by: Greer Prettyman
When you are trying to learn a new skill, who do you look to for examples? As children, we most often look to our parents and teachers as models of behavior. Other animals also learn socially, particularly those that need to learn complex skills. One such animal is the zebra finch, a type of small bird mostly found in Australia. Young male zebra finches learn to sing intricate songs. However, learning to sing isn’t just a hobby for these birds—it is crucial for male zebra finches to learn and perform their mating songs in order to successfully find mates and propagate their species.
Each male zebra finch learns an individualized version of a mating song. Typically, an adult male tutors the young bird, demonstrating his own song which the young bird begins to copy. Songs are often similar within a family, with a son’s song being a variation of his father’s. During a critical window of development, birds listen to this tutor’s singing and are able to learn their own song very quickly1. Eventually, the song “crystallizes” and they sing it the same way every time, forming their signature song. Human children also have this critical period for learning, which is why a toddler can learn an entire language in a few years but you may still be struggling to pick up a few French phrases before your trip abroad.
Neuroscientists often study zebra finches to understand the circuitry in the brain that allows these birds to learn and reproduce songs. Learning about the circuitry that underlies this singing behavior in birds also sheds light on a very similar basal ganglia circuit in the human brain that is required for producing motor movements.
Scientists have identified circuitry in the brain that is necessary for the zebra finch to learn, perfect, and perform this singing behavior (Figure 1). One part of the circuit is required for the production of a song (Figure 1, peach). An area called the HVC (which is just a name, not an acronym) receives auditory inputs. The HVC projects to the robust nucleus of the arcopallium (RA) which in turn connects to the vocal production center called the syrinx and respiratory centers, allowing motor production necessary for singing2.
Another cortical-basal ganglia circuit known as the anterior forebrain pathway (AFP) is critical for song learning, rather than song production (Figure 1, lavender). This circuit involves projections from the HVC and the lateral magnocellular nucleus of the anterior neostriatum (LMAN) to a region called Area X, part of the basal ganglia. By lesioning, or removing, different regions of birds’ brains and observing how normal song learning changed, scientists could determine what specific parts of song learning are controlled by which parts of the circuit. Young birds that had lesions in the LMAN showed almost no variability in the notes of their songs, suggesting that this region is important for producing the variability necessary for song learning3. In contrast, juvenile birds with lesions to Area X produced songs that were highly variable even into adulthood, suggesting that this region is required for a bird to reduce variability over time and crystallize its one consistent song.
A large part of song learning depends on receiving feedback and learning from mistakes. This is the same way humans learn from reinforcement, such as hearing the discord from playing the wrong note on the piano and learning to correct the mistake the next time you practice. If birds are made deaf after hearing a tutor song, they do not learn a song effectively since they cannot receive auditory feedback from their own vocalizations4. The main neurotransmitter that meditates this feedback-based learning is dopamine. Interestingly, this same neurotransmitter is disrupted in a human disorder involving the basal ganglia circuit, Parkinson’s disease.
While scientists have learned a lot about the neural circuitry underlying bird song, less is known about how the social aspect of song learning is encoded in these brain regions. Recent research highlights an important aspect of social song learning—who the teacher is5. Songbirds learn better from a live tutor than from a recording6, and prefer tutors of their own species compared to other species of songbirds.
Young zebra finch also learn better from tutor songs that are sung directly to them compared to an undirected song of a bird singing in their vicinity7. Hearing a song directly from a tutor led to specific changes in activation of neurons in the song learning circuitry. Birds that heard a directed song from a tutor had greater activation in neurons that release the neurotransmitter dopamine in the ventral tegmental area (VTA) compared to birds that heard songs that weren’t directed to them and birds that received no tutoring at all (Figure 1, yellow).
Another study found that another midbrain area, the periaqueductal grey (PAG) had more activation in dopaminergic neurons when young birds listened to a song from a tutor5. These dopaminergic neurons from the PAG usually send signals to the HVC, a region described above that is critical for song learning. When researchers blocked the dopaminergic signals from PAG to HVC while a young bird heard a tutor song, the bird did not learn to copy the song. Conversely, activating these neurons in the lab while a song was played over the speaker led to the young birds learning the song just as they would from a live tutor. Together, these experiments indicate that this dopaminergic connection from PAG to HVC is involved in social learning.
Another interesting finding was that tutors who sang directly to a young bird also changed their own singing behavior, such as repeating certain notes and leaving longer pauses between motifs7. This pattern of behavior is very similar to the way adult humans switch to baby talk when communicating with babies.
Researching birdsong behavior helps scientists to understand how birds learn these amazingly complex behaviors and also how similar networks in the human brain allow us to learn complex behaviors of our own. Additionally, studying how birds learn from social information provides a unique insight into processes that are difficult to study directly in the human brain, such as social transmission of language, tradition, and culture.
References
1. Gobes, S. M. H., Jennings, R. B., & Maeda, R. K. (2019). The sensitive period for auditory-vocal learning in the zebra finch: Consequences of limited-model availability and multiple-tutor paradigms on song imitation. Behavioural Processes, 163, 5–12.
2. Doupe, A. J., Perkel, D. J., Reiner, A., & Stern, E. A. (2005). Birdbrains could teach basal ganglia research a new song. Trends in Neurosciences, 28(7), 353–363.
3. Scharff, C., & Nottebohm, F. (1991). A comparative study of the behavioral deficits following lesions of various parts of the zebra finch song system: implications for vocal learning. The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 11(9), 2896–2913.
4. Konishi, M. (1965). The role of auditory feedback in the control of vocalization in the white-crowned sparrow. Zeitschrift Fur Tierpsychologie, 22(7), 770–783.
5. Tanaka, M., Sun, F., Li, Y., & Mooney, R. (n.d.). A mesocortical dopamine circuit enables the cultural transmission of vocal behavior.
6. Derégnaucourt, S., Poirier, C., Kant, A. Van der, Linden, A. Van der, & Gahr, M. (2013). Comparisons of different methods to train a young zebra finch (Taeniopygia guttata) to learn a song. Journal of Physiology-Paris, 107(3), 210–218.
7. Chen, Y., Matheson, L. E., & Sakata, J. T. (2016). Mechanisms underlying the social enhancement of vocal learning in songbirds. Proceedings of the National Academy of Sciences of the United States of America, 113(24), 6641–6646.
Images
Cover Image from via Wikimedia Commons by Pradeep717 – Own work, CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:ZebraFinchMaleCaptiveIndia.jpg
Figure 1 created with BioRender.
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