Neural mechanisms for learned birdsong

Abstract

Learning by imitation is essential for transmitting many aspects of human culture, including speech, language, art, and music. How the human brain enables imitation remains a mystery, but the underlying neural mechanisms must harness sensory feedback to adaptively modify performance in reference to the object of imitation. Although examples of imitative learning in nonhuman animals are relatively rare, juvenile songbirds learn to sing by copying the song of an adult tutor. The delineation of neural circuits for birdsong raises the promise that this complex form of vocal learning, which bears strong parallels to human speech learning, can be understood in terms of underlying neural mechanisms. This promise is now being more fully realized, with recent experimental advances leading to better understanding of the central motor codes for song and the central mechanisms by which auditory experience modifies song motor commands to enable vocal learning.

Test of a motor theory of long-term auditory memory

“…The neural mechanism is unknown, but, to elaborate on our speculative proposal, this mechanism could involve a multistep process mediated in large part by the AF, in which: (i) signals in temporoparietal cortex produced by processing a novel, fluctuating speech sound would be transmitted via the AF to the ventrolateral frontal cortex and, from there, via corticostriatal pathways (41), signals can be transmitted to the striatum for mapping onto representations of a sequence of articulation and coarticulation plans for reproducing that sound (39,42); (ii) signals representing this covert, oromotor sequence would then be fed back to the temporoparietal cortex via the AF's reciprocal projections (43,44); and (iii) these repackaged signals representing the newly integrated auditory-oromotor sequence would be processed by the lateral temporal auditory stream and transmitted to the medial temporal lobe, where they would be initially encoded and stored. This proposal of a motor theory for speech recognition is similar in some respects to one proposed for vocal learning by songbirds (45,46), including the critical step (ii above) of an oromotor feedback or corollary discharge to auditory cortex, thereby establishing a precise sensorimotor correspondence between audition and vocalization.…”

Glutamatergic circuits in the song system of Zebra Finch brain determined by gene expression of Vglut2 and Glutamate receptors

“…In songbirds, song production and maintenance involve networks of interconnected brain nuclei, known as the song system, which consist of two pathways ( Fig. 1 Mooney, 2009). The posterior forebrain pathway, or motor pathway, connects the HVC (letter-based proper name), the robust nucleus of the arcopallium (RA), and the tracheosyringeal motor nucleus of the hypoglossal nerve (nXIIts).…”

Auditory–vocal mirroring in songbirds

“…Furthermore, songbirds and humans are both specialized for low-frequency hearing and display similar auditory perceptual capabilities, including a capacity for categorical perception of learned vocalizations [21][22][23]. And despite the evolutionary distance separating songbirds and humans, birdsong and speech exhibit strong developmental and neural parallels, including juvenile critical periods for auditory and vocal motor learning, a developmental progression from fragmentary babbling vocalizations to more complex, sequential and stereotyped vocal patterns, and specialized sensorimotor circuits that play an essential role in vocal learning, production and perception [15,17,19,24].…”