Abnormal Functional Connectivity Within Default Mode Network and Salience Network Related to Tinnitus Severity

Abstract

Background: Previous studies have demonstrated that tinnitus is associated with neural changes in the cerebral cortex. This study is aimed at investigating the central nervous characteristics of tinnitus patients with different severity by using a rs-EEG.

Participants and methods: rs-EEG was recorded in fifty-seven patients with chronic tinnitus and twenty-seven healthy controls. Tinnitus patients were divided into moderate-to-severe tinnitus group and slight-to-mild tinnitus group based on their Tinnitus Handicap Inventory (THI) scores. Source localization and functional connectivity analyses were used to measure the changes in central levels and examine the altered network patterns. The correlation between functional connectivity and tinnitus severity was analyzed.

Result: Compared to the healthy controls, all tinnitus patients showed significant activation in the auditory cortex (middle temporal lobe, BA 21), while moderate-to-severe tinnitus group showed enhanced connectivity between the parahippocampus and posterior cingulate gyrus. Moreover, the moderate-to-severe tinnitus group had enhanced functional connectivity between auditory cortex and insula compared to the slight-to-mild tinnitus group. The connections between the insula and the parahippocampal and posterior cingulate gyrus were positively correlated with THI scores.

Conclusion: The current study reveals that patients with moderate-to-severe tinnitus demonstrate greater changes in the central brain areas, including the auditory cortex, insula, parahippocampus and posterior cingulate gyrus. In addition, enhanced connections were found between the insula and the auditory cortex, as well as the posterior cingulate gyrus and the parahippocampus, which suggests abnormality in the auditory network, salience network, and default mode network. Specifically, the insula is the core region of the neural pathway that is composed of the auditory cortex, insula, and parahippocampus/posterior cingulate gyrus. This suggests that the severity of tinnitus is affected by multiple brain regions.

Keywords: Central nervous characteristics; Electroencephalogram; Functional connectivity; Severity; Tinnitus.

Fig. 1

Audiogram showing the average hearing thresholds from all tinnitus patients. Hearing thresholds for the group average are plotted for the left ear (left panel) and right ear (right panel), separately. The error bar represents standard deviation of the mean

Fig. 2

Standardized low-resolution brain electromagnetic tomography. Compared with the healthy controls, the slight-to-mild tinnitus group a and the moderate-to-severe tinnitus group b both had significantly increased activity in the middle temporal lobe (BA 21) for the beta2 frequency band. Labels L, R, A, and P represent left, right, anterior, and posterior, respectively

Fig. 3

Functional connectivity maps. a Compared with the healthy group, the moderate-to-severe tinnitus group had significantly enhanced functional connectivity between parahippocampus (PHC) and posterior cingulate cortex (PCC) in beta2 frequency band. b Compared with the slight-to-mild tinnitus group, the moderate-to-severe tinnitus group had significantly enhanced between auditory cortex (AUD) and insula (INS) in gamma frequency band. Labels L and R represent left and right, respectively

Fig. 4

The positive correlation between the strength of functional connectivity and THI scores in all tinnitus patients. a Correlation of the connection strength between insula (INS) and posterior cingulate cortex (PCC) (left) with the THI scores. b Correlation of the connection strength between the insula (INS) and the parahippocampus (PHC) with the THI scores. Labels L and R represent left and right, respectively

Fig. 5

Schematic representation of the changes in functional connectivity in tinnitus patients