Transcranial magnetic stimulation for the treatment of tinnitus: Effects on cortical excitability

Background: Low frequency repetitive transcranial magnetic stimulation ( rTMS) has been proposed as an innovative treatment for chronic tinnitus. The aim of the present study was to elucidate the underlying mechanism and to evaluate the relationship between clinical outcome and changes in cortical excitability. We investigated ten patients with chronic tinnitus who participated in a sham- controlled crossover treatment trial. Magnetic- resonance- imaging and positronemissiontomography guided 1 Hz rTMS were performed over the auditory cortex on 5 consecutive days. Active and sham treatments were separated by one week. Parameters of cortical excitability ( motor thresholds, intracortical inhibition, intracortical facilitation, cortical silent period) were measured serially before and after rTMS treatment by using single- and paired- pulse transcranial magnetic stimulation. Clinical improvement was assessed with a standardized tinnitusquestionnaire. Results: We noted a significant interaction between treatment response and changes in motor cortex excitability during active rTMS. Specifically, clinical improvement was associated with an increase in intracortical inhibition, intracortical facilitation and a prolongation of the cortical silent period. These results indicate that intraindividual changes in cortical excitability may serve as a correlate of response to rTMS treatment. Conclusion: The observed alterations of cortical excitability suggest that low frequency rTMS may evoke long- term- depression like effects resulting in an improvement of subcortical inhibitory function.