High-frequency priming stimulation does not enhance the effect of low-frequency rTMS in the treatment of tinnitus

Based on its ability to reduce the excitability of the cortex locally, low-frequency repetitive transcranial magnetic stimulation (rTMS) has been investigated for the treatment of hyperexcitability disorders such as auditory hallucinations and tinnitus. Results are promising, but characterized by only moderate improvement and a high inter-individual variability. Experimental data from motor cortex stimulation in healthy subjects indicates that the depressant effect of low-frequency rTMS can be enhanced by high-frequency priming stimulation. Here we will investigate whether high-frequency priming also improves the therapeutic efficacy of low-frequency rTMS in a clinical application. 32 patients with chronic tinnitus were randomly assigned to either a standard protocol of low-frequency rTMS (110% motor threshold, 1 Hz, 2000 stimuli/day) or a stimulation protocol in which priming stimulation with 6 Hz (90% motor threshold, 960 stimuli) preceded low-frequency rTMS (110% motor threshold, 1 Hz, 1040 stimuli/day). Stimulation was applied over the left auditory cortex by using MRI-guided coil positioning. The treatment outcome was assessed with a standardized tinnitus questionnaire. There was no significant difference between the standard protocol and the protocol involving priming stimulation. Both stimulation protocols resulted in significant clinical improvement after 10 days of stimulation, as compared to baseline. Our data does not support an enhancing effect of higher frequency priming on low-frequency rTMS in the treatment of tinnitus.