Broadened population-level frequency tuning in the auditory cortex of tinnitus patients

Abstract

Tinnitus is a phantom auditory perception without an external sound source and is one of the most common public health concerns that impair the quality of life of many individuals. However, its neural mechanisms remain unclear. We herein examined population-level frequency tuning in the auditory cortex of unilateral tinnitus patients with similar hearing levels in both ears using magnetoencephalography. We compared auditory-evoked neural activities elicited by a stimulation to the tinnitus and nontinnitus ears. Objective magnetoencephalographic data suggested that population-level frequency tuning corresponding to the tinnitus ear was significantly broader than that corresponding to the nontinnitus ear in the human auditory cortex. The results obtained support the hypothesis that pathological alterations in inhibitory neural networks play an important role in the perception of subjective tinnitus.NEW & NOTEWORTHY Although subjective tinnitus is one of the most common public health concerns that impair the quality of life of many individuals, no standard treatment or objective diagnostic method currently exists. We herein revealed that population-level frequency tuning was significantly broader in the tinnitus ear than in the nontinnitus ear. The results of the present study provide an insight into the development of an objective diagnostic method for subjective tinnitus.

Keywords: MEG; auditory-evoked response; brain; frequency tuning; magnetoencephalography; tinnitus.

Fig. 1.

Pure tone audiograms obtained from unilateral tinnitus patients. Filled and open squares indicate the mean hearing threshold levels (dB) in the tinnitus and nontinnitus ears, respectively. Error bars denote 95% confidence intervals.

Fig. 2.

Auditory-evoked magnetic fields of one representative participant. Top and bottom: graphs represent auditory-evoked fields elicited by the tinnitus ear stimulation and nontinnitus ear stimulation, respectively. Left and right: columns represent auditory-evoked fields elicited in silence and within band-eliminated noise, respectively.

Fig. 3.

Means of source strength waveforms across all participants (n = 7) and hemispheres. Solid lines represent the “Silent” condition and dashed lines represent the “Noisy” condition. Thin black lines represent the tinnitus ear stimulation and thick gray lines represent the nontinnitus ear stimulation.

Fig. 4.

Group means (n = 7) of N1m source strengths (left) and latencies (right) obtained by tinnitus and nontinnitus ear stimuli. Error bars denote the 95% confidence intervals obtained by boot-strap resampling tests (iteration = 100,000). Open and Filled bars denote the “Noisy” and “Silent” conditions, respectively.

Fig. 5.

Schematic figures of population-level frequency tuning. Left and right: columns represent neural activity elicited by a test stimulus without and with band-eliminated noise (BEN). Top and bottom: represent broad and sharp population-level frequency tuning, respectively. The 3 different colored areas represent 3 distinct neural groups: 1) neurons activated by BEN (light gray areas), 2) neurons activated by a test stimulus (dark gray areas), and 3) neurons activated by both BEN and a test stimulus (black areas).