Abstract
Subjective tinnitus is characterized by the perception of phantom sound without an external auditory stimulus. We hypothesized that abnormal functionally connected regions in the central nervous system might underlie the pathophysiology of chronic subjective tinnitus. Statistical significance of functional connectivity (FC) strength is affected by the regional autocorrelation coefficient (AC). In this study, we used resting-state functional MRI (fMRI) and measured regional mean FC strength (mean cross-correlation coefficient between a region and all other regions without taking into account the effect of AC (rGC) and with taking into account the effect of AC (rGCa) to elucidate brain regions related to tinnitus symptoms such as distress, depression and loudness. Consistent with previous studies, tinnitus loudness was not related to tinnitus-related distress and depressive state. Although both rGC and rGCa revealed similar brain regions where the values showed a statistically significant relationship with tinnitus-related symptoms, the regions for rGCa were more localized and more clearly delineated the regions related specifically to each symptom. The rGCa values in the bilateral rectus gyri were positively correlated and those in the bilateral anterior and middle cingulate gyri were negatively correlated with distress and depressive state. The rGCa values in the bilateral thalamus, the bilateral hippocampus, and the left caudate were positively correlated and those in the left medial superior frontal gyrus and the left posterior cingulate gyrus were negatively correlated with tinnitus loudness. These results suggest that distinct brain regions are responsible for tinnitus symptoms. The regions for distress and depressive state are known to be related to depression, while the regions for tinnitus loudness are known to be related to the default mode network and integration of multi-sensory information.
Highlights
Subjective tinnitus is a common and disturbing event, characterized by the perception of phantom sound or noise in the ear or head without an external auditory stimulus [1]
We reconfirmed that tinnitus distress or depression and tinnitus loudness are independent clinical factors
In accordance with these clinical observations, different regions were involved in tinnitus distress, depression and tinnitus loudness, respectively
Summary
Subjective tinnitus is a common and disturbing event, characterized by the perception of phantom sound or noise in the ear or head without an external auditory stimulus [1]. In general, tinnitus is an entirely subjective experience that can only be described by patient reports. About 20% of patients require medical or psychiatric treatment since tinnitus frequently triggers psychological problems and reduces quality of life through depression [4], insomnia [5], and distress [6]. Symptoms of tinnitus [7] are evaluated by (1) otologic examination, (2). Diagnostic pure tone audiometry for the assessment of hearing loss, (3) psychophysical measurements of tinnitus such as loudness match, pitch match, maskability and residual inhibition, and (4). At present, there is no sufficient and established objective diagnostic test to evaluate the severity and other characteristics of tinnitus
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