rTMS for the treatment of tinnitus: the role of neuronavigation for coil positioning.

Tinnitus affects 10% of the population, its pathophysiology remains incompletely understood, and treatment is elusive. Both animal models and functional imaging data in tinnitus patients suggest that tinnitus is associated with increased neuronal activity, increased synchronicity and functional reorganisation in the auditory cortex. Therefore, targeted modulation of auditory cortex has been proposed as a new therapeutic approach for chronic tinnitus. Repetitive transcranial magnetic stimulation (rTMS), a non invasive method for modulation of cortical activity, has been applied in different ways in patients with chronic tinnitus. Single sessions of high-frequency rTMS over the temporal cortex have been used to transiently interfere with the intensity of tinnitus. Repeated sessions of low-frequency rTMS have been investigated as a treatment for tinnitus. Here, we review data from clinical trials and discuss potential neurobiological mechanisms with special focus on the relevance of the stimulation target and the method of TMS coil positioning. Different functional neuroimaging techniques are used for detecting tinnitus-related changes in brain activity. They converge in the finding of increased neuronal activity in the central auditory system, but they differ in the exact localisation of these changes, which in turn results in uncertainty about the optimal target for rTMS treatment. In this context, it is not surprising that the currently available studies do not demonstrate clear evidence for superiority of neuronavigational coil positioning. Further development of rTMS as a treatment for tinnitus will depend on a more detailed understanding of both the neuronal correlates of the different forms of tinnitus and of the neurobiological effects mediating the benefit of TMS on tinnitus perception.