Organization, neuronal composition, and dynamics of neuronal ensembles in the songbird auditory forebrain.

Neurons involved in auditory learning are typically considered singly, but coincident activity of neuronal "ensembles" could be important for sensory processing. In songbirds, a higher-pallial region, the caudomedial nidopallium (NCM), is crucial for auditory learning. NCM neurons adapt to repeated presentation of song stimuli, a form of online recognition memory. Yet, how complex song stimuli are encoded by ensembles of excitatory and inhibitory neurons is unknown. Using high-density electrophysiology, we unveiled neuronal ensembles operating at high temporal precision across the NCM. Multiple ensembles are concurrently activated by songs, heterogeneously composed, topographically proximate, and biased toward excitatory members. NCM ensembles adapt to song playback and, notably, become more stimulus-selective over tens of minutes, accompanied by fast remodeling. Altogether, our results show that songs are conveyed by multiple, parallel dynamic network ensembles. These findings advance our knowledge of the composition, dynamics, and network reorganization of ensembles as complex sensory stimuli become increasingly familiar.