Somatotopy in the Inferior Colliculus: Implications for a New Tinnitus Treatment
The inferior colliculus (IC) is a midbrain auditory center that sends and receives signals to and from various auditory structures throughout the brain. Previous studies have identified superimposed somatotopic maps within the superior colliculus. Considering the large number of somatosensory projections to the IC and the involvement of the IC in the orienting reflex, we performed experiments to identify similar somatotopy within the IC. We positioned electrode arrays into the IC of anesthetized guinea pigs at various locations to form a square grid of placements across the entire IC. We characterized the responses in IC to subcutaneous electrical stimulation of several somatic sites. Stimulation of lower body areas activated more medial regions of the IC while stimulation of upper body areas activated more lateral regions. Similary, left-to-right body stimulation elicited responses in a rostral-to-caudal pattern. Although each body region projected predominantly to a unique IC area, there were also projections to overlapping regions across IC. The existence of somatotopy within an auditory-dominant nucleus reveals an even stronger coupling and organization among the different sensory modalities than previously reported. In response to these findings, we conceived of the idea of activating the somatosensory pathways to modulate auditory neurons for tinnitus treatment. We are currently investigating if stimulation across the body in a coordinated pattern can induce long-term changes within the central auditory system to suppress/fix the tinnitus-affected neurons. This research was supported by University of Minnesota start-up funds and NSFIGERT grant DGE-1069104.