Lateralization of functional magnetic resonance imaging (fMRI) activation in the auditory pathway of patients with lateralized tinnitus

INTRODUCTION: Tinnitus is hypothesized to be an auditory phantom phenomenonresulting from spontaneous neuronal activity somewhere along the auditorypathway. We performed fMRI of the entire auditory pathway, including the inferiorcolliculus (IC), the medial geniculate body (MGB) and the auditory cortex (AC),in 42 patients with tinnitus and 10 healthy volunteers to assess lateralizationof fMRI activation. METHODS: Subjects were scanned on a 3T MRI scanner. AT2*-weighted EPI silent gap sequence was used during the stimulation paradigm,which consisted of a blocked design of 12 epochs in which music presentedbinaurally through headphones, which was switched on and off for periods of 50 s.Using SPM2 software, single subject and group statistical parametric maps werecalculated. Lateralization of activation was assessed qualitatively andquantitatively. RESULTS: Tinnitus was lateralized in 35 patients (83%, 13right-sided and 22 left-sided). Significant signal change (P(corrected) < 0.05)was found bilaterally in the primary and secondary AC, the IC and the MGB. Signalchange was symmetrical in patients with bilateral tinnitus. In patients withlateralized tinnitus, fMRI activation was lateralized towards the side ofperceived tinnitus in the primary AC and IC in patients with right-sidedtinnitus, and in the MGB in patients with left-sided tinnitus. In healthyvolunteers, activation in the primary AC was left-lateralized. CONCLUSION: Ourparadigm adequately visualized the auditory pathways in tinnitus patients. Inlateralized tinnitus fMRI activation was also lateralized, supporting thehypothesis that tinnitus is an auditory phantom phenomenon.

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