Reduced ABR response and sound-evoked/resting-state BOLD fMRI connectivity in tinnitus
23 April 2019 (online)
The precise neurophysiological basis of chronic tinnitus, which affects 10 – 15% of the population, remains unknown and is controversial at many levels. It is an open question whether phantom sound perception results from increased central neural gain or rather a lack of central neural gain, a crucial aspect for future therapeutic intervention strategies for tinnitus. We studied normal to mild hearing-impaired participants with and without tinnitus, excluding the co-occurrences of hyperacusis. We used different audiological tests, fMRI measurements (during rest and with audiological stimuli) and cortisol analysis in body fluids. For the audiological test, we clinically exam the ears, did tympanometry and acoustic reflex measurements, performed pure tone and speech audiometry to determine the hearing threshold, scored tinnitus with a questionnaire and did ABR measurements. A 3-Tesla scanner (Siemens Skyra) was used for fMRI acquisition. Besides, resting state measurements for functional connectivity, different auditory stimuli (music and frequency-modulated chirp sounds) were used for task-evoked measurements.
We observed in the group of participants with tinnitus reduced and delayed sound-induced suprathreshold auditory brainstem responses (ABR wave V), reduced evoked BOLD fMRI responses in auditory midbrain and cortical regions, reduced resting state r-fcMRI connectivity between lower and higher level auditory brain regions and prefrontal regions (stress controlling). We conclude that reduced auditory-specific flow may hamper auditory-specific recruitment of prefrontal (stress controlling) regions as a correlate of tinnitus.