MEG localization of the putative cortical generators of tinnitus

.The purpose of the study was to determine the efficacy of magnetoencephalography (MEG) in establishing the cortical sites for electrical stimulation in patients with tinnitus. Two patients with debilitating tinnitus refractory to conventional therapies were treated. Each patient was evaluated with validated questionnaires and psychoacoustic measures to determine the frequency and pitch of their tinnitus. A tonotopic map of each patient's auditory cortex was established using MEG by applying tones of the targeted frequencies and pitch. MEG data was analyzed by Single Equivalent Current Dipole. Functional magnetic resonance imaging (fMRI) was performed to identify the entire auditory cortex during the presentation of music. fMRI data was analyzed by SPM. In both patients, the tonotopic match sites were targeted by a neuronavigation system for placement of an intracerebral electrode (Pisces quadripolar, Medtronic, Inc). Amplitudes were set to 0.1 V, pulse widths at 50 ms and the rate to 40 Hz. Electrode contacts were activated by random pattern and varied subsequently by the patients as needed. Patient #1 was implanted in the right hemisphere and followed for 2 years, and has had a significant reduction to near elimination of tinnitus. Patient #2 was implanted in the left hemisphere and followed for 2 months. This patient experienced elimination of the tinnitus in his left ear, but has an accentuation in his right ear. Until now, the consensus has been that there is no treatment that can eliminate or significantly reduce debilitating tinnitus. We have shown, in this pilot study of 2 patients, that the described methodology can have a significant impact on the reduction of tinnitus. These findings suggest that the perception and annoyance of tinnitus can be significantly reduced through electrical stimulation of the auditory cortex identified by MEG.