Asymmetry in primary auditory cortex activity in tinnitus patients and controls

Tinnitus is a bothersome phantom sound percept and its neural correlates are not yet disentangled. Previously published papers, using [(18)F]-fluoro-deoxyglucose positron emission tomography (FDG-PET), have suggested an increased metabolism in the left primary auditory cortex in tinnitus patients. This unilateral hyperactivity has been used as a target in localized treatments such as transcranial magnetic stimulation. The purpose of the current study was to test whether left-sided hyperactivity in the auditory cortex is specific to tinnitus or is a general characteristic of the auditory system unrelated to tinnitus. Therefore, FDG-PET was used to measure brain metabolism in 20 tinnitus patients and to compare their results to those in 19 control subjects without tinnitus. In contrast to our expectation, there was no hyperactivity associated with tinnitus. Nevertheless, the activity in the left primary auditory cortex was higher than in the right primary auditory cortex, but this asymmetry was present in both tinnitus patients and control subjects. In contrast, the lateralization in secondary auditory cortex was opposite, with higher activation in the right hemisphere. These data show that hemisphere asymmetries in the metabolic resting activity of the auditory cortex are present, but these are not associated with tinnitus and are a normal characteristic of the normal brain.