Auditory‐somatosensory integration in the auditory brainstem and its alteration after cochlear damage.

Abstract

In addition to auditory‐nerve inputs, the cochlear nucleus (CN) receives extensive non‐auditory inputs from somatosensory ganglia and brainstem nuclei [Shore et al., JCN (2000); Zhou and Shore JCN, (2007)]. The effects of stimulating these pathways on CN physiology are examined using multichannel technology to measure single‐ and multi‐unit activities across populations of neurons in both the dorsal and ventral divisions of the guinea pig CN. Neurons in both CN divisions show evidence of multisensory integration by exhibiting non‐linear summation of auditory nerve and somatosensory inputs. Thus, somatosensory neurons can suppress or enhance acoustically evoked response rates as well as altering their temporal patterns. These changes may explain why some patients with tinnitus can modulate the loudness and pitch of their tinnitus by somatic maneuvers of the head and neck. Exploring how these pathways change after various forms of deafness allows us to delve into the realm of neural plasticity, hyperacusis, and tinnitus. Noise induced deafness renders CN neurons more sensitive to somatosensory stimulation as well as increasing the spontaneous rates of those neurons responsive to these inputs [Shore et al., EJN (2008)], findings that can be explained by cross‐modal reinnervation [Zeng et al., J. Neurosci. (2009)].