Shore et al.

University of Michigan, Kresge Hearing Research Institute Ann Arbor, MI, USA

Somatic tinnitus patients can modulate both the intensity and pitch of their tinnitus by manipulating facial regions including their jaws and teeth, areas innervated by the trigeminal nerve. Over the past several years, we have demonstrated functional connections between the trigeminal system and the auditory brainstem and midbrain.

Stimulation of trigeminal neurons can produce changes in the spontaneous
and sound driven firing rates of cochlear nucleus (CN) and inferior olliculus (IC) neurons. These changes in firing rate could account for the intensity changes in their tinnitus perceived by patients. New data indicate that trigeminal neurons can also modify the temporal patterns of spontaneous and sound driven responses of CN neurons, often making the firing patterns more regular. Regular firing of neurons in the CN has been proposed as a model for pitch perception. Thus, if trigeminal neurons can change the regularity of auditory neurons’ firing patterns, they could alter the perceived pitch generated by those firing patterns.

We will also present evidence that after sound over-exposure, there are compensatory changes in non-auditory innervation of the CN. Our studies so far indicate that following deafness, these compensatory changes result in enhanced effects of trigeminal stimulation on the firing patterns in CN, as exhibited by lower thresholds and latencies in response to this stimulation. The physiological results reflect increases in glutamatergic inputs from non-auditory regions of the brain.

Understanding how somatic tinnitus occurs will help us to understand how tinnitus itself is generated. Only then can we hope to develop methods to alleviate this distressing condition.

Susan E. Shore
University of Michigan
Kresge Hearing Research Institute
Department of Otolaryngology
1301 E. Ann Street
Ann Arbor, MI 48109-0506, USA
E-Mail sushore@umich.edu
www.khri.med.umich.edu