Breaking news: A. Van der Es

Title: The influence of transcranial magnetic stimulation on the efferent auditory pathway

Field of research: Otorhinolaryngology

Keywords: TMS, efferent auditory pathway, TEOAE

Authors:

A. Van der Es BSc, L.I. Geven Drs, R.H. Free Dr, E. De Kleine Dr, P. Van Dijk Dr

Presenting author:

A. Van der Es BSc

 

Introduction:

Multiple studies have demonstrated that repetitive transcranial magnetic stimulation (rTMS) can alleviate tinnitus by modulating the excitability of the auditory cortex. This indicates that rTMS might represent a promising treatment for tinnitus. The inhibitory qualities of the efferent auditory pathway are suggested to be responsible for this therapeutic effect.
The aim of this study was to provide evidence for inhibition in the auditory pathway by rTMS. We hypothesized that, if an inhibitory efferent auditory pathway exist, stimulation of the auditory cortex via rTMS should alter the transient-evoked otoacoustic emissions (TEOAEs). We expected the emission amplitude to decrease. Furthermore, we wanted to determine whether a change in amplitude of the TEOAEs depended on the stimulation frequency used for rTMS.

Material & methods:

In a cross-over design, 15 healthy subjects were divided in three groups, receiving 1 Hz, 10 Hz and placebo rTMS applied over the left auditory cortex. During stimulation the subjects wore earplugs. The TEOAEs in the right ear were measured before and after the rTMS sessions. The amplitudes of the CEOAE before and after rTMS were compared in five half-octave frequency bands, centered at 1.0, 1.4, 2.0, 2.8 and 4.0 kHz. Data were analysed by a Wilcoxon signed ranks test, with statistical significance being defined as p<0.05.

Results:

Data showed an increase of the amplitude after 1 Hz, 10 Hz and placebo rTMS. After the 1-Hz session and after the 10-Hz session 12 subjects had an increase of amplitudes. Thirteen subjects showed an increase of the amplitudes after placebo rTMS. The differences between the amplitudes before and after rTMS were significant for all the conditions (1 Hz: p=0.08; 10 Hz: p=0.01 and placebo rTMS p=0.007).

Conclusion:

We detected an increase of TEOAE amplitudes for all rTMS stimulation protocols (1 Hz, 10 Hz and placebo). Possibly, there is a systematic drift in TEOAE emission amplitudes over the time course of an experimental session, for example due to the earplugs that seal the ears during rTMS. This is currently under investigation.