Abstract
Increased spontaneous activity and aberrant neural synchrony is thought to be the underlying cause of tinnitus. The perceived pitch of tinnitus may be dictated by frequency specific neural fibers of the subcortical pathway, or the projection of altered cortical activity by-way-of tonotopic reorganizations. Subcortical neural activity in relation to tinnitus was characterized using ABR measurements. In the present study, 11 patients (21 ears) with constant tonal tinnitus underwent a two-part experiment. Experiment 1 involved click ABR measurements and included two experimental groups: tinnitus with normal hearing from 2000-4000 Hz (GI) and tinnitus with hearing loss within the range of 2000-4000 Hz (GII). Experiment 2 utilized tone burst ABRs matched to each participant's perceived tinnitus pitch and included two experimental groups: tinnitus with normal hearing at the tinnitus pitch (GIa) and tinnitus with hearing loss at the tinnitus pitch (GIIa). These groups were compared to a control group (GIII) of ten monaurally tested (10 ears) participants with normal hearing thresholds at 250-20000 Hz and no tinnitus. Click ABR results indicate significantly prolonged V-III IPLs for GI and GII and a significantly extended absolute V latency for GII only. Tone burst ABRs matched to tinnitus pitch revealed significantly prolonged absolute latencies and IPLs at three of the seven frequencies for GIIa. ABR threshold seeking was completed and revealed negative eHL values for two of the four different stimuli for GI and GIa and four of the eight stimuli for GII and GIIa. Click ABRs results are suggestive of upper brainstem abnormalities for both groups. While GI demonstrated prolonged V-III IPLs, no significant differences were found for GIa. This suggests that there is no frequency specific subcortical characteristic associated with tinnitus with normal hearing. Frequency specific properties for subcortical activity could not be characterized due to varying results of GIIa.
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