Responses to natural species-specific and artificial nonspecific sounds in the medial nidopallium and mesopallium of adult male starlings
Résumé
The 'song control system' has been defined as a set of interconnected brain nuclei found only in songbirds. These nuclei have a clear and primary role in the motor control of song production. The neural systems responsible for sensory representation of songs are less well defined. Recently, however, a forebrain region distinct from the song nuclei has emerged as a plausible site for sensory representation of birdsong. This region, which includes parts of the medial nidopallium and mesopallium that are analogue to the mammalian auditory cortex, was initially identified through studies of immediate early gene responses to sounds, and has been very rarely investigated through electrophysiological studies, especially in birds showing multiple song types. Here, neuronal responses to a variety of natural species-specific and artificial non-specific stimuli were systematically recorded in the medial nidopallium and mesopallium of awake-restrained adult male starlings. Starlings are highly social songbirds that exhibit a very complex song behaviour. Our results show that non-specific stimuli were significantly less effective in driving neuronal responses than species-specific stimuli. Furthermore, a vast majority of the neurons responded to warbling motifs. These motifs are known to play a crucial role in individual recognition. Finally, we could observe a remarkably clear and unexpected functional organisation throughout the medial nidopallium and mesopallium. These results bring original clues to sensory representation of birdsong in the forebrain and represent a significant step towards a better understanding of the processes that support discrimination and categorical perception of learned vocalizations.