The Roles of Subdivisions of Human Insula in Emotion Perception and Auditory Processing

Previous studies have shown insular activations involving sensory, motor, and affective processing. However, the functional roles of subdivisions within the human insula are still not well understood. In the present study, we used intracranial electroencephalography and electrical cortical stimulation to investigate the causal roles of subdivisions of the insula in auditory emotion perception in epilepsy patients implanted with depth electrodes in this brain region. The posterior and the anterior subdivisions of the human insula, identified based on structural and functional analyses, showed distinct response properties to auditory emotional stimuli. The posterior insula showed auditory responses that resemble those observed in Heschl's gyrus, whereas the anterior insula (AI) responded to the emotional contents of the auditory stimuli in a similar way as observed in the amygdala. Furthermore, the degree of the differentiation between various emotion types increased from the posterior to the AI. Our findings suggest different roles played by the two regions of the human insula and a transformation from sensory to affective representations in auditory modality along the posterior-to-anterior axis in the human insula.