UC San Diego

Vocal recognition is important for communication in several species, including humans. Songbirds learn to recognize the vocalizations of conspecifics for social behaviors such as mate attraction and territorial defense. We examined the role of the caudomedial nidopallium (NCM), a forebrain region analogous to secondary auditory cortices, in song recognition. We trained European starlings to recognize conspecific songs and recorded the activity of single neurons in NCM. In ventral NCM, neurons responded stronger to unfamiliar songs than to songs that starlings had learned to recognize. While in dorsal NCM, neurons responded similarly to learned and unfamiliar songs. In a second experiment we trained starlings to recognize songs and exposed them to an equal number of songs passively. Recognition learning weakened the firing rates to the learned songs, while passively hearing songs had no effect, indicating that the response suppression in NCM requires associative learning. These results show that song recognition learning weakens the responses to learned songs in ventral NCM. Local inhibition is involved in the plasticity of sensory systems that results from altered sensory input such as deprivation. To investigate the mechanisms underlying the plasticity in NCM, we manipulated local inhibition in NCM of starlings that were trained to recognize conspecific songs. Blocking inhibition enhanced the preference for unfamiliar songs in ventral NCM and uncovered a preference for learned songs in dorsal NCM. Disrupting inhibition reduced the selectivity for songs and uncovered responses to specific regions of song that are normally masked. In dorsal NCM, a greater frequency of these unmasked responses occurred during learned songs. Blocking inhibition also increased the nonlinearities associated with spectro-temporal receptive fields. This demonstrates that local inhibition modulates learning-related plasticity by inactivating plasticity throughout NCM