In response to a brief input from the primary AC, a simulated BS neuron receives a burst of excitation followed by delayed and prolonged inhibition (Figure 8A, inset). Based on this temporal filter, we simulated the spiking

activity of BS neurons (n = 70), each of which received as input the responses Hydroxychloroquine supplier of an individual primary AC neuron (n = 70) to songs, chorus, and auditory scenes. Primary AC activity was simulated using receptive fields estimated from responses to songs (Calabrese et al., 2011). Simulations of this circuit transformed dense and continuous primary AC responses to song into sparse responses that were selective for a subset of songs, firing reliably in response to specific notes (Figure 8B). The firing rate, selectivity, and sparseness of simulated BS neurons were similar to those GSK1349572 in vivo observed in experimentally recorded BS neurons (Figure S7). In response to auditory scenes at SNRs above 0 dB, simulated BS neurons produced precise spike trains similar to those produced in response to the song presented alone, and at low SNRs, most simulated BS neurons stopped firing (Figure 8C). As in recorded responses, simulated BS neurons extracted individual songs from auditory

scenes better than simulated primary AC neurons at high and intermediate SNRs (Figure 8D). Using raw PSTHs from primary AC neurons as inputs to the model rather than simulated PSTHs produced similar results (data not shown). Together, these simulations show that a cortical circuit of feedforward inhibition can accurately reproduce the emergence of sparse and background-invariant song representations. We report a population of auditory neurons that produce background-invariant responses to vocalizations at SNRs that match behavioral

recognition thresholds. Individual BS neurons in the higher-level AC respond sparsely and selectively to a subset of songs, in contrast to NS neurons and upstream populations. BS neurons largely retain their song-specific firing patterns in levels of background sound that permit behavioral recognition and stop firing at SNRs Dextrose that preclude behavioral recognition. These results suggest that the activity of BS neurons in the higher-level AC may serve as a neural mechanism for the perceptual extraction of target vocalizations from complex auditory scenes that include the temporally overlapping vocalizations of multiple individuals. To measure behavioral recognition, we trained birds to report the identity of an individual song presented simultaneously with a distracting chorus using a Go/NoGo task. Although Go/NoGo behaviors are typically described as discrimination tasks, a variety of strategies could be used to perform the task, all of which require subjects to detect target sounds but not necessarily to discriminate among them.