Abstract
Tinnitus is the perception of an internally generated sound that is postulated to emerge as a result of structural and functional changes in the brain. However, the precise pathophysiology of tinnitus remains unknown. Llinas’ thalamocortical dysrhythmia model suggests that neural deafferentation due to hearing loss causes a dysregulation of coherent activity between thalamus and auditory cortex. This leads to a pathological coupling of theta and gamma oscillatory activity in the resting state, localised to the auditory cortex where normally alpha oscillations should occur. Numerous studies also suggest that tinnitus perception relies on the interplay between auditory and non-auditory brain areas. According to the Global Brain Model, a network of global fronto—parietal—cingulate areas is important in the generation and maintenance of the conscious perception of tinnitus. Thus, the distress experienced by many individuals with tinnitus is related to the top—down influence of this global network on auditory areas. In this magnetoencephalographic study, we compare resting-state oscillatory activity of tinnitus participants and normal-hearing controls to examine effects on spectral power as well as functional and effective connectivity. The analysis is based on beamformer source projection and an atlas-based region-of-interest approach. We find increased functional connectivity within the auditory cortices in the alpha band. A significant increase is also found for the effective connectivity from a global brain network to the auditory cortices in the alpha and beta bands. We do not find evidence of effects on spectral power. Overall, our results provide only limited support for the thalamocortical dysrhythmia and Global Brain models of tinnitus.
Highlights
Subjective idiopathic tinnitus (TI) refers to a phantom sound that is consciously perceived without an external physical source
While we find a significant difference in effective connectivity between ACs and the global component in the beta band such an effect is absent in the functional connectivity analysis
We find a significant increase in functional connectivity for TI in the theta and alpha bands
Summary
Subjective idiopathic tinnitus (TI) refers to a phantom sound that is consciously perceived without an external physical source. The thalamus fires at around 10 Hz in the resting awake state, driving the connected parts of the cortex to oscillate at the same frequency This alpha activity is thought to be consequence of a mechanism of pulsed cortical inhibition [10,11,12]. Abnormal gamma oscillations appear as an “edge effect” in neurons surrounding the theta-locked areas of the auditory cortex and form the neurophysiological correlate of the conscious TI percept (see Fig. 1A). According to this model, theta and gamma activity should arise from different but adjacent locations on the auditory cortex. A definite prediction remains difficult, and an absence of such changes, or changes in other frequency bands cannot be regarded as evidence against the models, as discussed in the Introduction
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
