Assessing tinnitus and prospective tinnitus therapeutics using a psychophysical animal model

Subjective tinnitus is a common and often debilitating disorder that is dif ficult to study because it is a perceptual state without an objective stimu lus correlate. Studying tinnitus in humans is further complicated by the he terogeneity of tinnitus quality, severity, and associated hearing loss. As a consequence, the pathophysiology of tinnitus is poorly understood and tre atments are often unsuccessful. In the present study, an animal psychophysi cal model was developed to reflect several features of tinnitus observed in humans. Chronic tinnitus was induced in rats by a single intense unilatera l exposure to noise. The tinnitus was measured using a psychophysical proce dure, which required the animals to discriminate between auditory test stim uli consisting of tones, noise, and 0 dB. Tinnitus was indicated by a frequ ency-specific shift in discrimination functions with respect to control sub jects not exposed to noise. The psychophysical consequences of the noise ex posure were best explained by a tinnitus hypothesis and could not be explai ned easily by other consequences of noise exposure such as hearing loss. Th e qualitative features of the tinnitus were determined and related to the d uration of noise exposure and the associated cochlear trauma. The tinnitus was found to persist and intensify over 17 months of testing. Finally, the tinnitus was reversibly attenuated by treatment with gabapentin, a GABA ago nist. It was concluded that this model reflected several features of human tinnitus, such as its tonality and persistence, and could be useful as a sc reen for potential therapeutics as well as a tool to help unravel the patho physiology of the disorder of phantom auditory perception.