ATA-FUNDED RESEARCH
rTMS for the Treatment of Chronic Tinnitus: Optimization by Stimulation of the Cortical Tinnitus Network
by Astrid Lehner,
Dipl.Psych., Martin Schecklmann, Ph.D., Berthold Langguth, M.D., Ph.D. Intent of Our Work
Repetitive transcranial magnetic stimulation (rTMS) of auditory brain regions has been applied as a treatment option in patients with chronic tinnitus for several years. This technique works with magnetic fields which “normalize” brain activity in the auditory cortex (AC). Forty to fifty percent of patients treated with rTMS experience a reduction in their tinnitus. Recent studies suggest additional “non-auditory” brain regions may play a role in tinnitus as well. Therefore, we tried to find out if an extension of rTMS to non-auditory brain areas is able to enhance treatment effects. We also aim to gain more insight into the neural correlates of chronic tinnitus by using neuroimaging methods before and after rTMS.
Chronic Subjective Tinnitus: Neural Correlates and rTMS
Scientists have dealt with the causes of tinnitus for many years now and although we have still not found the key to turning it off, many important insights con- cerning its generation and manifestation were gained during the past decade. Some years ago, scientists realized that the long-held assumption that tinnitus was an inner-ear issue was not truly the case. They began to focus on the auditory pathway – the route starting in the ear and leading to the AC in the brain.
Realizing the relevance of the brain for generation and maintenance of tinnitus was a milestone in tinnitus research and brought many scientists to examine tinnitus-related alterations within the auditory path- way. Studies which analyzed the structure and activ- ity of auditory brain regions found abnormalities. For example, the AC is more active in tinnitus patients. This led to the idea that if the hyperactivity could be reduced, this should have an effect on the tinnitus percept. As a result, new treatment approaches were developed which target this hyperactivity of the AC.
One of those treatment approaches is repetitive tran- scranial magnetic stimulation. rTMS is a technique which applies strong magnetic fields to the brain for modulating neural activity. The magnetic fields are produced within a coil which is placed on the scalp
12 Tinnitus Today | Summer 2012
(Figure 1) and are able to influence the activity of neurons lying beneath the coil. If placed over the AC, rTMS is assumed to normalize the altered AC activity and ease tinnitus complaints. For this purpose, rTMS is usually applied on 10 consecutive working days with each of the sessions lasting about 30 to 45 minutes. In recent years, many studies have shown that rTMS is able to reduce tinnitus severity in some patients. The effects of this treatment are only small to moder- ate however.
Figure 1. Transcranial magnetic stimulation for the treatment of tinnitus.
This is where the second important milestone of tinnitus research comes into play. Recent studies suggest that in order to fully understand the neural correlates of chronic tinnitus it is not enough to solely concentrate on altered activity within the auditory pathway. Rather, non-auditory brain areas should be additionally taken into account. It is understood that a sound – no matter if it is a “normal” sound or tinnitus – only enters consciousness if non-auditory areas are involved in its processing. Some studies have found alterations of the activity within these non-auditory structures in patients with tinnitus.
Currently, this theory of both auditory and non-audi- tory brain areas being important for tinnitus is being refined by some scientists. The idea is emerging that we should not concentrate on the activity within each of these brain regions separately, but instead focus
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