The auditory sensitivity is increased in tinnitus ears

Abstract

Increased auditory sensitivity, also called hyperacusis, is a pervasive complaint of people with tinnitus. The high prevalence of hyperacusis in tinnitus subjects suggests that both symptoms have a common origin. It has been suggested that they may result from a maladjusted increase of central gain attributable to sensory deafferentation. More specifically, tinnitus and hyperacusis could result from an increase of spontaneous and stimulus-induced activity, respectively. One prediction of this hypothesis is that auditory sensitivity should be increased in tinnitus compared with non-tinnitus subjects. The purpose of this study was to test this prediction by examining the loudness functions in tinnitus ears (n = 124) compared with non-tinnitus human ears (n = 106). Because tinnitus is often accompanied by hearing loss and that hearing loss makes it difficult to disentangle hypersensitivity (hyperacusis) to loudness recruitment, tinnitus and non-tinnitus ears were carefully matched for hearing loss. Our results show that auditory sensitivity is enhanced in tinnitus subjects compared with non-tinnitus subjects, including subjects with normal audiograms. We interpreted these findings as compatible with a maladaptive central gain in tinnitus.

Figure 1.

Distribution (top) and cumulative distribution (bottom) of auditory sensitivity scores obtained from the Khalfa questionnaire. Nearly 80% of control participants (white squares) present a score below 10, whereas the percentage is 40% in the tinnitus group (black squares), indicating that auditory sensitivity is enhanced in tinnitus participants.

Figure 2.

The dynamic range (discomfort level − absolute threshold) for the three frequencies tested (1, 2, and 4 kHz) as a function of the hearing-loss category. Control (white squares) and tinnitus (black squares) ear groups are significantly different at all three frequencies only in the group in which the absolute thresholds were within normal range. Hearing-loss category: 0, normal hearing; 1, slight hearing loss; 2, mild hearing loss; 3, moderate-to-profound hearing loss.

Figure 3.

Mean absolute thresholds and discomfort levels for tinnitus (black squares) and control (white squares) ears. Absolute thresholds are within normal range at all frequencies, but the dynamic range was lower at all tested frequencies in the tinnitus ears.

Figure 4.

Averaged loudness functions obtained from tinnitus (black squares) and control (white squares) normal-hearing ears at 1 (A) and 4 kHz/edge (B).

Figure 5.

A, B, Slopes of loudness functions obtained at 4 kHz/edge from tinnitus (plain lines) and control (dotted lines) ears for normal hearing (A) and slight hearing loss (B).

Figure 6.

A–D, Averaged loudness functions obtained from tinnitus ears for 1 kHz (A) and 4 kHz (B) and control ears for 1 kHz (C) and 4 kHz (D), with respect to hearing-loss category (from 0 to 3). Loudness curves in tinnitus ears remain essentially parallel at high sound levels, whereas control ears display typical loudness recruitment curves.