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Abstract

Cortical auditory system organization comprises a number of responsive areas that span a region in the primate forebrain extending from the temporal lobe to the frontal lobe. These areas collaborate in structured networks where sensory information is distributed into several processing streams. In this context, human imaging studies provide preliminary evidence to suggest a role for the insula cortex in auditory processing, especially in processing speech and language. In this study we electrophysiologically characterize the primate insula cortex in terms of its auditory capabilities. To facilitate the interpretation of our findings, we systematically compare the response properties of insular neurons to those of neurons in the primary and secondary auditory cortices.
Our findings identify an acoustically responsive region in the posterior insula cortex that is activated by both simplistic as well as naturalistic sounds. Although these insular neurons exhibit response properties similar to neurons in auditory cortex such as responsiveness to simple stimuli and tuning to sound frequency, they also differ from auditory cortical neurons in that they express longer latencies and that they do not sensitively represent the sound envelope. Individual stimuli are encoded sparsely across the population of neurons within the insula, yet these neurons are more selective to particular natural sounds than auditory cortical neurons. Interestingly, primate insular neurons demonstrate a preference for conspecific vocalizations. Furthermore, we are also able to identify a differential response to different vocalization types. Our findings thus suggest a role for the insula cortex in processing and representing auditory information preferentially vocalizations.