The blinking eye as a window into tinnitus: A new animal model of tinnitus in the macaque

Tinnitus is a highly prevalent, largely untreatable auditory disorder, characterized by the perception of phantom sound often in the form of incessant ringing or hissing. Despite longstanding research with animal models, its underlying pathophysiological causes remain poorly understood. Given recent data characterizing tinnitus as a disorder with a strong neurocognitive component, progress in the field might be hastened by testing a wider spectrum of animal models, including nonhuman primates, and by developing alternative measurement techniques of tinnitus, especially in animals. To provide fresh impetus, we developed a novel tinnitus-verification technique applicable to rhesus monkeys. Tinnitus was induced via salicylate administration in two monkeys, and was confirmed by applying a specific eyeblink procedure: Blinks, as monitored with EMG, were triggered via puffs of air towards the cheek, and their modulation was studied as a function of preceding tones under various frequency and intensity conditions. The advantage of a tactile reflex-inducing stimulus lies in its non-auditory modality, bypassing potential confounding factors of hearing loss and hyperacusis. Interference effects on the blink modulation pattern were interpreted as tinnitus, and the frequency of the preceding interfering tone as tinnitus frequency. A cross-validation in a sample of human tinnitus patients revealed interfering effects of the preceding tone in the specific frequency range corresponding to their own tinnitus frequency, as independently determined by audiologists. This interference effect increased as a function of individual tinnitus loudness. In conclusion, the present work demonstrates considerable transferability of a newly established tinnitus-verification technique from nonhuman primates to human tinnitus patients. The technique may be usable both for objective measurements of tinnitus in human patients as well as a potential alternative technique for routine tinnitus testing in animal models.