Social context bidirectionally modulates VTA/SNc responses to tutor song in juvenile zebra finches

Social interaction facilitates vocal learning more effectively than passive exposure, but the neural signals that reflect the social context of auditory experience remain unclear. Midbrain dopaminergic circuits broadcast motivational and learning-related signals, raising the possibility that VTA/SNc activity may reflect both tutor-song auditory input and tutor presence during juvenile vocal development. We tested this idea in juvenile zebra finches by recording single-unit activity during the same tutor-song playback under tutor-absent and tutor-present conditions; in the tutor-present condition, a live tutor was present but remained silent. Among 185 VTA/SNc neurons from 8 birds, tutor presence bidirectionally modulated auditory responses. Type-1 neurons showed enhancement (46/185, 24.9%), whereas Type-2 neurons showed suppression (29/185, 15.7%). Both profiles were observed in all birds, and bird-level analyses supported consistent modulation. Type-1 neurons showed increased baseline firing and a further enhancement of baseline-subtracted song-evoked responses, whereas Type-2 suppression occurred without reduced baseline firing. Using spike waveform and firing rate criteria, we found that the tutor-enhanced Type-1 population included neurons with putative dopaminergic features. In naturalistic recordings, these neurons also showed increased activity during live tutor singing. These findings suggest that socially modulated VTA/SNc activity may link tutor presence to auditory processing relevant to vocal learning.