The effect of rTMS on auditory processing in adults with chronic, bilateral tinnitus: a placebo-controlled pilot study

Background: On the basis that tinnitus may result from neural hyperactivity in the auditory cortex, researchers have investigated the use of low frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS) as a potential modulator of this hyperactivity. While these investigations show promise, investigations to date have neglected to consider the possible effect of 1 Hz rTMS on other functions of the auditory cortex of these individuals, such as auditory processing.

Objective/hypothesis: This placebo-controlled pilot study aimed to determine whether 1 Hz rTMS applied to the primary auditory cortex (PAC), specifically Brodmann Area 41 (BA41), of adults with chronic, bilateral tinnitus would influence their auditory processing abilities.

Methods: Eight participants with bilateral, chronic tinnitus were randomized to receive a 10-day course of neuronavigationally guided active rTMS (n = 4) or placebo rTMS (n = 4) treatment applied to a focal region of the left PAC (BA41). Participants' auditory processing was measured using Time Compressed Reverberant Speech and three-pair Dichotic Digits (DD). Their tinnitus was measured using the Tinnitus Handicap Inventory (THI) and a psychoacoustic measure of tinnitus perception. All outcome measures were administered at baseline (1 week prior to rTMS), 1 week, 1, 2 and 3 months post-rTMS.

Results: All four participants in the active rTMS (A) group, and none of the participants in the sham (placebo) rTMS (S) group, showed improved auditory processing scores at multiple assessment points post-stimulation, with the group differences in median normalized gain scores reaching significance at the 5% level from 1 week or 1 month post-stimulation onwards. Three of the four participants in the active rTMS (A) group, and none of the participants in the sham rTMS (S) group, showed improved tinnitus scores at multiple assessment points post-stimulation, with some of the group differences in median normalized gain scores reaching significance at the 5% level.

Conclusions: The results of this preliminary study suggest that 1 Hz rTMS applied to the PAC (BA41) has the capacity to improve both auditory processing and tinnitus perception in some adults with chronic, bilateral tinnitus.