"Neural Processing of Complex Sounds in the Primate Auditory Cortex"
ABSTRACT
Compared with the visual or somatosensory system, the ascending pathway leading to the cortex is much longer in the auditory system. A consequence of such a long serial processing pathway is that the temporal precision of stimulus-locked spikes is progressively degraded due to synaptic integrations at each stage. However, auditory perception often depends on fine timing information in acoustic signals. Our recent study showed that auditory cortex solves this problem by performing temporal-to-rate transformations. Cortical neurons mark sparse acoustic events with precise spike timing and transform rapidly occurring acoustic events into firing rate-based representations. Another challenge facing the auditory system is that acoustic signals in natural environment are highly overlapping in spectral domain and subsequently in their peripheral neural representations. The auditory system must identify a sound from competing sources in order to form an auditory object. We found that neurons in auditory cortex selectively process local spectral profiles of complex sounds and integrate contextual inputs from a broad range of frequencies, far beyond the region surrounding a neurons receptive field. Inhibition instead of facilitation dominates interactions between harmonically related frequency components. These findings indicate that an important function of the auditory cortex is to segregate a target signal from background noises or other concurrent sounds. Findings from these and other studies suggest that neural representations of complex sounds in the auditory cortex are transformed and abstracted from overlapping and competing signals in acoustic environment, and may serve as the basis for object recognition in the auditory system.