Like many great musicians, songbirds hone their tuneful tweeting talents by learning from a singing coach, and a new study in the journal Nature Communications has now revealed the neurological mechanism underpinning this process.
The fact that many birds copy the vocalizations of their role models – most commonly their parents – is nothing new. Their ability to do so suggests that they must somehow be able to store a precise memory of their tutors’ song, using this as a reference against which to tune their own melodious singing. However, exactly how they achieve this had until now eluded researchers.
Previous studies have come close to disentangling the mystery, with one study indicating that blocking signaling pathways in a part of the brain called the caudomedial nidopallium (NCM) reduces a young bird’s ability to mimic its parents’ songs. It therefore seems likely that the NCM may act as a storage site for song memory in the birds’ brains.
To test this, researchers measured the electrical responses of neurons in the brains of young zebra finches while in the process of song learning. Using a loudspeaker, the scientists played each bird nine different recordings, one of which was of that bird’s tutor while the others were of songs belonging to other birds.
Intriguingly, neurons in the NCM showed a surge in activity whenever a bird heard a recording of its tutor’s song, yet not in response to any of the other eight songs. As such, the study authors write that it is indeed highly likely that “tutor song memory may be represented in a subset of NCM neurons.”
Taking their work a step further, the team decided to investigate how this learning process actually takes place. Previous research has shown that sensory tuning in the brain is largely controlled by a neurotransmitter called GABA, which inhibits neurons. As the brain develops and is exposed to a range of sensory stimuli, fluctuating levels of GABA help to set a balance between inhibition and excitation, effectively fine-tuning the brain by regulating the precision of the neuronal response to these stimuli.
The researchers therefore suspected that GABA may play a key role in songbirds’ ability to recall the pitch of their tutors’ songs and reproduce this in their own vocalizations. To test this hypothesis, they injected the birds with a pharmacological agent that blocks GABA in the brain, and found that this reduced the ability of neurons in the NCM to recognize and respond to the songs of their parents.
Though this work relates specifically to the way that songbirds learn to tune their auditory responses, the authors believe that studying birdsong neurology further may also provide some key insights into how humans acquire speech and language.