Effective connectivity analysis of inter- and intramodular hubs in phantom sound perception - identifying the core...

Tinnitus, the perception of a phantom sound, is accompanied by loudness and distress components. Distress however accompanies not just tinnitus, but several disorders. Several functional connectivity studies show that distress is characterized by disconnectivity of fronto-limbic circuits or hyperconnectivity of default mode/salience networks. The drawback, however, is that it considers only the magnitude of connectivity, not the direction. Thus, the current study aims to identify the core network of the domain-general distress component in tinnitus by comparing whole brain directed functional networks calculated from 5 min of resting state EEG data collected from 310 tinnitus patients and 256 non-tinnitus controls. We observe a reorganization of the overall tinnitus network, reflected by a decrease in strength and efficiency of information transfer between fronto-limbic and medial temporal regions, forming the main hubs of the tinnitus network. Further, a disconnection amongst a subset of these connections was observed to correlate with distress, forming a core distress network. The core distress network showed a decrease in strength of connections specifically going from the left hippocampus/parahippocampus to the subgenual anterior cingulate cortex. Such a disconnection suggests that the parahippocampal contextual memory has little influence on the (paradoxical) value that is attached to the phantom sound and that distress is the consequence of the absence of modulation of the phantom sound.