Cortical representation of complex spectrotemporal features in songbirds

Mechanistic understanding of how the auditory cortex processes complex communication signals remains a challenge. With their rich vocal communication behaviors, songbirds can offer insights into this question. We investigated the neural representation of sound features in the cortical auditory areas of zebra finches. In the primary cortical area field L, our systematic mapping of spectrotemporal receptive fields revealed a highly organized representation in which sharpness of spectral and temporal tuning of sound is mapped along two separate anatomical axes. The clustering of temporally or spectrally selective neurons suggested that initial cortical filtering for basic perceptual qualities such as tempo and pitch occurs in a spatially organized and segregated manner. Moreover, using an information theoretic based technique, we are uncovering additional sound features beyond those represented by conventional spectrotemporal receptive fields. In field L, we find that many neurons encode a second feature that typically captures rapid spectral or temporal modulations overlapping the first feature. In the secondary auditory area CM, a major target of field L, we are discovering an emergent sensitivity to frequency stacks, prevalent in zebra finch vocalizations. Together, our data show a systematic and hierarchical mapping of sound features onto songbird cortical neurons.