Some forms of tinnitus may involve the extralemniscal auditory pathway

TLDR

Previous studies show that click‑evoked brainstem responses are normal in tinnitus patients, except for a significantly shortened peak V latency compared to hearing‑loss controls. This study tests whether the extralemniscal auditory system contributes to tinnitus generation. The authors used median‑nerve electrical stimulation to exploit the somatosensory input to extralemniscal neurons and probe auditory‑somatosensory interactions. Median‑nerve stimulation altered tinnitus in 10 of 26 patients—four increased, six decreased—while the remaining 16 showed no change; the tinnitus character sometimes changed, hearing thresholds were unchanged, and stimulation had no effect on loudness in 12 normal‑hearing controls.

Abstract

Abstract It has previously been shown that the click‐evoked responses recorded from the intracranial portion of the eighth nerve in patients with incapacitating tinnitus are not abnormal, nor is the latency of peak III of the click‐evoked brainstem auditory‐evoked potentials significantly altered; however, the latency of peak V is slightly (but significantly) shortened in comparison to that of patients with the same degree of hearing loss but no tinnitus. In this study the hypothesis that the extralemniscal auditory system is involved in the generation of tinnitus is tested. We made use of the fact that neurons of the extralemniscal auditory system also receive input from the somatosensory system, and that stimulation of the somatosensory system can influence the processing of auditory information in the extralemniscal system. In 4 of 26 patients with mild‐to‐severe tinnitus whose median nerve was stimulated electrically, the tinnitus increased noticeably during stimulation, in 6 the intensity of the tinnitus decreased noticeably, and in the remaining 16 there was no noticeable change in the tinnitus. In some of the patients the character of the tinnitus changed in a complex way. There were no significant differences in hearing thresholds in these three groups of patients. Electrical stimulation of the median nerve in 12 individuals with normal hearing who did not have tinnitus either had no effect on the loudness of sounds or it caused a slight increase in the loudness.