Strategies for enhancement of transcranial magnetic stimulation effects in tinnitus patients.

Tinnitus is an auditory phantom sensation characterized by the perception of elementary sound or noise in the absence of any acoustical sound source. Tinnitus is a frequent disorder and is difficult to treat. Compelling evidence corroborates the perception of chronic tinnitus as associated with regional changes in cortical excitability. Repetitive transcranial magnetic stimulation (rTMS) over the temporal or the temporoparietal cortex has recently been introduced as a new treatment strategy for tinnitus. The technique has been applied in two different ways in tinnitus patients. Single sessions of high-frequency rTMS have been successful in transient reduction of tinnitus perception, whereas repeated sessions of low-frequency rTMS have resulted in longer-lasting tinnitus reduction, indicating therapeutic potential. However, treatment outcome so far is characterized by high interindividual variability and only moderate effect size. This study reviews different approaches for enhancement of rTMS effects in tinnitus patients. The different strategies include the combined stimulation of nonauditory and auditory brain areas, the variation of stimulation frequencies and intensities, and the comparison of different firing modes (burst vs. tonic stimulation). Furthermore, the value of optimum patient selection is discussed. Another approach consists of a combination of rTMS administration with pharmacological intervention. Repetition of rTMS treatment in treatment responders seems to be a promising approach for the prolongation of treatment effects. A pilot study suggests further that treatment effects can be enhanced by combined stimulation of auditory and nonauditory brain areas. Moreover, clinical data such as tinnitus duration and the dimension of hearing loss seem to have an important impact on treatment effects. Successful enhancement of treatment effects will depend on a more detailed understanding of the neuronal correlates of the different forms of tinnitus and the mechanisms by which rTMS exerts its effects.