Hitting the right notes makes zebra finches feel good
Charles Darwin learnt a lot from finches, but the little birds still have much to teach us. Amy Middleton reports.
Singing the right notes gives zebra finches a dopamine hit, new research suggests.
A research team led by Vikram Gadagkar, a neurobiologist at Cornell University in New York, set about matching birdsong performance with dopamine – a brain chemical related to our reward and pleasure centres.
Although many behaviours are learnt through trial and error, the brain’s evaluation process is poorly understood, the researchers write in Science.
“When practicing piano, how do you know if you struck the right or wrong note?” the report asks. “There is nothing intrinsically ‘good’ or ‘bad’ about the sound of A-sharp. It entirely depends if that’s the note you wanted to strike at that time step of the song.”
The researchers use this analogy to explain how sensory feedback helps us evaluate how our performance compares with the internal benchmarks we set for ourselves.
In humans, an error can cause a negative signal in the dopamine neurons that relate to the brain’s ventral tegmental area (VTA), which is closely associated with rewards.
Zebra finches (Taeniopygia guttata), it turns out, respond to their own singing in a similar fashion. To establish this, Gadagkar’s team played the birds audio recordings of species-specific song, some with added errors, while measuring VTA neuron activity.
Sure enough, in a huge majority of cases, a distorted song dropped dopamine activity.
Interestingly, on hearing the song again without the error, the same group of neurons were activated in a way that suggests the birds were expecting to hear it again. Not doing so produced a “better than predicted” response.
This hints that birds remember previous mistakes, and adjust their performance benchmarks accordingly, which could help explain how young birds learn to imitate their elders so accurately.
Meanwhile, in another paper in Science, molecular neurobiologist Makoto Araki at Okinawa Institute of Science and Technology Graduate University in Japan and colleagues focused on how zebra finches know which song to imitate, despite being raised around multiple species. The paper suggests that the answer might lie in the spaces between sounds.
“In the zebra finch auditory cortex, we discovered a class of neurons that register the silent temporal gaps between song syllables and are distinct from neurons encoding syllable morphology,” the researchers write.
The team studied finches raised by Bengalese finch parents, paying close attention to the songs that resulted from this family dynamic.
They found that during the vocal learning period, temporal gap neurons fired selectively to zebra finch songs, suggesting birds have an innate neuronal barcode for species-specific vocal learning and social communication.
In a commentary accompanying the two studies, psychologists Ofer Tchernichovski and Dina Lipkind of Hunter College in New York suggest these findings could shine a light on wider animal communication systems, and perhaps even the retention of stable cultures among humans.