Many species of birds share with humans a capacity for vocal learning, according to a review published in the journal Brain & Language.
There is a remarkable genetic and neural parallel between birdsong and human voice production, and the study suggested that this may have important consequences for understanding the evolution of auditory-vocal learning and its neural mechanisms.
AdvertisementProduction of learned vocal expressions is confined only to humans, bats, dolphins, elephants, and sea lions among mammals, and in zebra finches, canaries, crows, parrots and hummingbirds among birds.
Human brains are asymmetric and language tends to be organized in the left hemisphere as opposed to the right. Birds are also often assumed to show similar hemispheric specialization for song. And the brain chemical responsible for this is dopamine.
Dopamine is a neurotransmitter produced in several areas of the brain and plays an important role in brain processes that control movement, emotional response, and ability to experience pleasure and pain.
Cases have been reported where dopamine receptor antagonists (drugs blocking dopamine receptors) temporarily disrupted normal vocal motor control, especially seen in neurological and psychiatric patients with voice and speech problems, such as Parkinson's disease (PD), stuttering, Tourette's syndrome, and schizophrenia. The evidence thus indicates the major role played by dopamine in proper execution of motor commands and cognitive processing associated with speech production.
Similarly, in birds, dopamine release from the front part of the brain and into the nerves in the brainstem that control muscle movements triggers bird song.
The behavioral mechanisms of vocal learning to produce human speech and birds song are thought to be similar because 'both have the critical periods for vocal learning in early life before adulthood and require auditory experience and feedback to develop and maintain their learned vocal sequences'.
However, there are a couple of differences, according to the researchers. First, while humans are able to learn new vocal expressions throughout the lifespan, some birds such as zebra finches are not able to imitate new songs well, if at all, in adulthood, and others such as African Grey parrots, have only limited ability to imitate new sounds as adults. Secondly, birds use most of their songs for affective communication while human speech use semantic communication.
The researchers concluded 'Due to similarities with humans in the ability to produce learned vocalizations, songbirds present a potentially useful model to study some shared mechanisms of dopaminergic transmission underlying speech and song production. However, as humans possess several unique features of speech control, human dopaminergic regulation may need to be studied in humans only'.
Reference: Simonyan, K., et al. Dopamine regulation of human speech and bird song: A critical review. Brain & Language (2012), doi:10.1016/j.bandl.2011.12.009
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