Abstract
Chronic tinnitus is a brain network disorder with involvement of auditory and non-auditory areas. Repetitive transcranial magnetic stimulation (rTMS) over the temporal cortex has been investigated for the treatment of tinnitus. Several small studies suggest that motor cortex excitability is altered in people with tinnitus. We retrospectively analysed data from 231 patients with chronic tinnitus and 120 healthy controls by pooling data from different studies. Variables of interest were resting motor threshold (RMT), short-interval intra-cortical inhibition (SICI), intra-cortical facilitation (ICF), and cortical silent period (CSP). 118 patients were tested twice - before and after ten rTMS treatment sessions over the left temporal cortex. In tinnitus patients SICI and ICF were increased and CSP was shortened as compared to healthy controls. There was no group difference in RMT. Treatment related amelioration of tinnitus symptoms were correlated with normalisations in SICI. These findings confirm earlier studies of abnormal motor cortex excitability in tinnitus patients. Moreover our longitudinal data suggest that altered SICI may reflect a state parameter, whereas CSP and ICF may rather mirror a trait-like predisposing factor of tinnitus. These findings are new and innovative as they enlarge the knowledge about basic physiologic and neuroplastic processes in tinnitus.
Highlights
Tinnitus is associated with neural changes in both the auditory pathway, and in non-auditory brain areas [1]
Group contrasts of two big samples of patients with tinnitus (n = 231) and healthy controls (n = 120) revealed significant differences in short-interval intra-cortical inhibition (SICI), intra-cortical facilitation (ICF; with a statistical trend), and cortical silent period (CSP)
Tinnitus is known to be related to neural changes along the auditory pathway emerging from a dysbalance of inhibitory and excitatory neurons [18]
Summary
Tinnitus is associated with neural changes in both the auditory pathway (increase of spontaneous stochastic firing rate, hyperactivity, alterations of the tonotopic map), and in non-auditory brain areas [1]. [2,3]) seem to reflect pathologically altered brain networks, which develops as a response to abnormal sensory input [4]. Based on these findings repetitive transcranial magnetic stimulation (rTMS) was introduced as a treatment approach in tinnitus [5]. ICF was found to be enhanced in 19 patients with tinnitus in contrast to 19 controls [6] and CSP was found to be shortened (37 patients vs 12 controls) [7] It is not known whether these findings are state or trait parameters. They could either represent cross-modal plasticity like changes accompanying tinnitus, or unspecific general neural mechanisms reflecting individual predisposition factors for developing tinnitus
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