A rapid anterior auditory processing stream through the insulo-parietal auditory field in the rat

The insular cortex is 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 female 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 adjacent non-primary somatosensory fields. Confirming previous reports, neurons in this field had narrow tuning, and were preferentially tuned to relatively low frequencies (<16 kHz). Intriguingly, auditory units in this field displayed shorter minimal latencies than units in primary auditory cortex, as well as weaker sensitivity to deviance. These results establish the existence of a rapid auditory information stream with distinct properties through the insulo-parietal cortex that may parallel the pathway through the primary and anterior auditory fields. Significance statement This study unveils a fast auditory processing stream with distinct properties that bypasses primary auditory cortex in the rat brain. Utilizing neuropixels electrodes, we confirmed the presence of an auditory field at the insulo-parietal junction with an over-representation of low frequencies. Neurons in this field have remarkably short response latencies as well as weaker sensitivity to deviant sounds than core auditory areas. This research offers a new perspective on the involvement of insular and parietal cortices in the rapid processing of sounds.