Cortical Representations of Auditory Phantom Perception (Tinnitus)

Tinnitus has originally been seen as a disturbance of the peripheral auditory system. In view of the fact that tinnitus can persist even after surgical transection of the cochlear nerve, the hypothesis evolved that it could be a phenomenon similar to phantom pain and a consequence of maladaptive neuronal plasticity (cf. Jastreboff Neurosci Res 1990: 8: 221). The terms 'centralization of tinnitus' or 'central tinnitus' have been used to differentiate chronic subjective tinnitus from acute or objective forms. In the present study we sought to identify cortical representations of chronic subjective tinnitus. Regional cerebral blood flow associated with tinnitus perception was measured with H₂ ¹⁵O positron emission tomography (PET). Two conditions were statistically compared, a baseline condition when patients had their typical tinnitus sensation and a condition in which tinnitus was suppressed by an intravenous bolus injection of 1.5mg/kg lidocaine. The patients (n=9) had a total of four scans on two separate days. The data were processed with statistical parametric mapping (SPM99). Significance of increased rCBF during tinnitus perception was tested in a fixed effects analysis (multi-subjects, conditions and covariates) and random effects analysis (one sample t-test based on the individual contrast images). Increased rCBF was consistently found in left secondary auditory areas (BA 42, 22), the region of the angular gyrus (BA 39), and in right prefrontal areas (BA 9, 11). These results identify a neocortical network involving prefrontal and secondary auditory areas which could underlie the perception of tinnitus. Ongoing experiments in our laboratory are geared at the question whether neurostimulation of this tinnitus-related neural network can alleviate symptoms in patients suffering from chronic subjective tinnitus.