Speech Comprehension Difficulties in Chronic Tinnitus and Its Relation to Hyperacusis.

Objective: Many tinnitus patients complain about difficulties regarding speech comprehension. In spite of the high clinical relevance little is known about underlying mechanisms and predisposing factors. Here, we performed an exploratory investigation in a large sample of tinnitus patients to (1) estimate the prevalence of speech comprehension difficulties among tinnitus patients, to (2) compare subjective reports of speech comprehension difficulties with behavioral measurements in a standardized speech comprehension test and to (3) explore underlying mechanisms by analyzing the relationship between speech comprehension difficulties and peripheral hearing function (pure tone audiogram), as well as with co-morbid hyperacusis as a central auditory processing disorder. Subjects and Methods: Speech comprehension was assessed in 361 tinnitus patients presenting between 07/2012 and 08/2014 at the Interdisciplinary Tinnitus Clinic at the University of Regensburg. The assessment included standard audiological assessments (pure tone audiometry, tinnitus pitch, and loudness matching), the Goettingen sentence test (in quiet) for speech audiometric evaluation, two questions about hyperacusis, and two questions about speech comprehension in quiet and noisy environments ("How would you rate your ability to understand speech?"; "How would you rate your ability to follow a conversation when multiple people are speaking simultaneously?"). Results: Subjectively-reported speech comprehension deficits are frequent among tinnitus patients, especially in noisy environments (cocktail party situation). 74.2% of all investigated patients showed disturbed speech comprehension (indicated by values above 21.5 dB SPL in the Goettingen sentence test). Subjective speech comprehension complaints (both for general and in noisy environment) were correlated with hearing level and with audiologically-assessed speech comprehension ability. In contrast, co-morbid hyperacusis was only correlated with speech comprehension difficulties in noisy environments, but not with speech comprehension difficulties in general. Conclusion: Speech comprehension deficits are frequent among tinnitus patients. Whereas speech comprehension deficits in quiet environments are primarily due to peripheral hearing loss, speech comprehension deficits in noisy environments are related to both peripheral hearing loss and dysfunctional central auditory processing. Disturbed speech comprehension in noisy environments might be modulated by a central inhibitory deficit. In addition, attentional and cognitive aspects may play a role.

Behavioral auditory thresholds and loss of ribbon synapses at inner hair cells in aged gerbils.

The potential contribution of auditory synaptopathy to age dependent hearing loss was studied in groups of young and old gerbils. The analysis of the number of inner hair cell ribbon synapses in aged gerbils (37.9±3.3months of age) revealed only a relatively small (11-17%) loss in the basal two thirds of the cochlea, while a more pronounced reduction was identified towards the apex (almost 40%) when compared to a group of young gerbils (9.5±3.2months of age). Mean threshold elevation in the old gerbils was around 25dB at 2 and 10kHz. Frequency-specific behavioral thresholds and ribbon synapse counts were not significantly correlated for the middle and basal regions of the cochlea, despite thresholds varying over a 45dB SPL range. This suggests that besides a small age-dependent loss of ribbon synapses, additional cochlear pathologies, most likely a decreased endocochlear potential, contribute to peripheral hearing loss in old gerbils.