A Rapid Anterior Auditory Processing Stream Through the Insulo-Parietal Auditory Field in the Rat

The insular cortex is believed to be involved in a wide range of auditory functions in the mammalian brain. We studied the organization and basic response properties of auditory neurons in insular cortex and adjacent areas by recording responses to sound stimuli in anesthetized rats. Auditory neurons were present in an insulo-parietal auditory field that spans the boundary between the posterior insula, particularly in the granular insular cortex and the ventral part of the secondary somatosensory cortex. Neurons in this field had narrow tuning, were preferentially tuned to relatively low frequencies (<16 kHz), and had short response latencies. Intriguingly, some auditory units in this insulo-parietal field displayed shorter onset latencies than the minimal latency in primary auditory cortex. At the same time, these units showed weaker sensitivity to deviance than units in primary auditory cortex. These results establish the existence of a rapid information stream through the insulo-parietal cortex that may parallel the pathway through the primary and anterior auditory fields.