Investigating neural mechanisms of intrinsic motivation for non-courtship singing in zebra finches

초록

Intrinsic motivation drives animals, including humans, to engage in various voluntary behaviors that originate within the brain, independent of external stimuli such as rewards or punishments. Songbirds, such as zebra finches, provide an excellent model for studying the neural substrates of intrinsic motivation, as they spontaneously produce numerous renditions of non-courtship song (or "undirected song") with a highly quantifiable structure for vocal practice. We recently found that a septal area, the nucleus of the hippocampal commissure (NHpC), is activated when intrinsic motivation for undirected singing is enhanced by behavioral manipulation (Mori et al., 2025, Sci Rep). In the present study, we examined whether the NHpC is directly involved in regulating undirected singing motivation by assessing the effects of electrolytic lesions in NHpC on undirected singing behavior. Our results showed that NHpC lesions had no significant effect on either the daily amount of undirected singing or the behaviorally-induced enhancement of undirected singing motivation. These findings do not support the hypothesis that the NHpC plays a critical role in regulating undirected singing motivation, suggesting instead that brain areas connected to the NHpC may be directly involved. To further explore the neural circuitry underlying undirected singing motivation, we performed neuroanatomical analyses using neuronal tracers injected into the NHpC. Our preliminary results suggest that the NHpC receives axonal projections from the midbrain ventral tegmental area (VTA) and projects to the medial portion of the dorsolateral nucleus of the thalamus (DLM), a thalamic region specialized for song learning and plasticity. Together, these findings offer new insights into the neural mechanisms regulating intrinsic motivation for non-courtship singing in songbirds.