A sensorimotor area (NIf) is required for the production of learned vocalizations

Sensory feedback is essential for the acquisition of complex motor behaviors, including birdsong. In zebra finches, auditory feedback is relayed to the descending motor pathway primarily through the nucleus interfacialis nidopalii (NIf). NIf projects to HVC - a premotor region essential for song, which projects to RA, a motor cortex analogue brain area that drives muscle activity required for vocalizations. NIf is also essential for ‘sleep replay’, a recapitulation of song-related neural dynamics in the motor pathway during sleep. Despite being one of the major inputs to the song control pathway, there is no known role for NIf in the production of zebra finch song. To address this, we reversibly inactivated NIf using TTX or Muscimol in 13 birds. We compared songs before and during inactivation and found large effects of NIf inactivation on song structure. Vocalizations after NIf inactivation resembled subsong, highly variable utterances typical of the very early phases of song learning. Subsong is driven by LMAN, the output nucleus of an avian basal ganglia circuit that projects to RA. To verify that NIf inactivations indeed switched song control from HVC to LMAN, we inactivated LMAN in conjunction with NIf in four birds. As with LMAN inactivations after HVC lesions, this manipulation led to a complete cessation of singing. We also lesioned NIf using ibotenic acid and saw the song recover within a day, consistent with previous studies. Our results show that NIf input to HVC is acutely necessary for generating learned vocal behavior in songbirds, and that in its absence vocal production reverts to subsong driven by LMAN. Absent NIf input, the song circuit reorganizes and recovers its ability to produce pre-lesion song over the course of 1-2 days, suggesting a redundant role for NIf that can be assumed by other parts of the song circuit