Dornhoffer lab DornhofferJohnL@uams

Subjective tinnitus, the perception of sound in the absence of acoustic stimulation, is a common phenomenon, affecting approximately 17% of the general population.  About one-fourth of these individuals seek professional help due to associated mood, sleep, and attentional disturbances.  The exact mechanisms of tinnitus generation and the related central nervous system dysfunction are unknown, making diagnosis and treatment difficult and often empirical.  While most believe that the inciting event for tinnitus generation lies in cochlear or auditory nerve dysfunction, the perception of tinnitus can be ascribed to central mechanisms in most cases.  Although many tinnitus sufferers complain of poor concentration, neuropsychological testing has revealed that the cognitive defficiency appears to be associated with the control of attention, especially the inhibition of attention task–irrelevant activity.

We used the sleep state-dependent midlatency auditory evoked P50 potential to assess the level of arousal and of habituation to repetitive stimuli in tinnitus patients and in age- and gender-matched control subjects.  No significant difference in the amplitude of the P50 potential was evident between individuals with tinnitus and age-matched controls.  This suggests that tinnitus patients have no detectable impairment in the level of arousal using the P50 potential.   There were, however, significant differences in habituation in the tinnitus group at the 250-msec and 1000-msec ISI.  This is in agreement with Hallum’s theory that tinnitus represents a fundamental deficit in habituation.  Impaired habituation leading to a sensory gating deficit may explain some of the attentional deficits and cognitive disturbances described in tinnitus patients.  Our findings, likewise, are in agreement with a subcortical source of habituation and suggest a deficit in sensory gating may be present in tinnitus sufferers.