Identification of the neural circuits involved in intrinsic motivationfor voluntary vocal behavior in songbirds

초록

Intrinsic motivation drives animals, including humans, to exhibit various voluntary behaviors, originating within the brain without external stimuli such as rewards or punishments. Songbirds such as zebra finches provide an ideal model for studying neural substrates of intrinsic motivation because they spontaneously produce many renditions of non-courtship song with highly quantifiable structure for vocal practice. Here, we examined the neural circuits involved in intrinsic motivation for non-courtship singing in adult zebra finches by conducting whole-brain mapping of neuronal activation using immediate early gene expression and neuroanatomical analysis using neuronal tracers. We found that birds with relatively high singing motivation exhibit increased expression levels of an immediate early gene Arc in a septal area, the nucleus of the hippocampal commissure (NHpC), compared with birds with low singing motivation. These results indicate that NHpC neurons are activated contingent on the degree of intrinsic singing motivation, suggesting that NHpC neurons are involved in regulating intrinsic singing motivation. Moreover, our neuroanatomical analysis using neuronal tracers including a retrograde GFP virus demonstrates that NHpC receives axonal projections from the midbrain ventral tegmental area (VTA) and has reciprocal connections with the medial nucleus of the dorsolateral thalamus (DLM), a thalamic nucleus specialized for song learning and plasticity. These findings provide an important initial step in understanding the neural circuitry regulating intrinsic motivation for non-courtship singing behavior in songbirds, offering a new avenue to study neural substrates of intrinsic motivation for voluntary behavior.