Audiovisual interactions in the cortical-like primary auditory area of a songbird
Résumé
Data on both songbirds and humans suggest that there is a very tight coupling between vocal behaviour and social cognition. However, the question of how this coupling works remains completely open, and further studies are clearly needed to advance our understanding of the neurobiological components that link vocal brains to social brains. Songbirds are to date the best developed model to study language-like processes in the brain. Indeed, songbirds are, with humans, among the rare species that learn to produce their vocalizations. Furthermore, song, like language, is a multimodal behaviour. Behavioural studies have shown that visual stimuli could for example enhance song learning, and that social interactions per se are crucial for song behaviour to develop properly. Thus, given that stimulations with no auditory component can influence song behaviour, and that mere auditory experience is not sufficient for song learning to occur, there must be some neural structures in the vocalauditory system that are sensitive to non-auditory feedback. In mammals, there has been large evidence of multisensory integration in low-level putatively unisensory brain regions in a variety of species, including humans. However, to date, no study could provide evidence of multisensory interactions in sensory regions involved in the perception of song. Here, we provide the first evidence of audiovisual interactions in the cortical-like primary auditory area of a highly social songbird, the European starling. For that, we recorded neuronal responses to species-specific songs presented either alone or together with a visual stimulus. Our results showed that a substantial proportion (42%) of auditoryresponsive neuronal sites exhibited responses that were significantly modulated by the corresponding visual component. Although the visual stimulus itself caused no activation, it modified those to some auditory stimuli. To our knowledge, this is the first evidence of audiovisual interactions in a cortical-like primary auditory area of a non-mammalian vertebrate brain. Moreover, these interactions were strongly stimulus dependent, and the auditory stimuli to which the responses were enhanced by the presentation of a visual stimulus were unfamiliar, whereas stimuli to which the responses were reduced were familiar/own stimuli, suggesting that selective attention might be crucial.