Repetitive Transcranial Magnetic Stimulation in patients with hearing loss

In the noisy environment of the normal daily life, the comprehension of sound and speech requires a good functioning of the auditory system. Hearing loss (HL) is the permanent partial/total inability to perceive sounds and it is usually accompanied by whole ears-brain pathways modification and a marked reduced ability to perceive stimuli, especially with a background noise. Removable hearing aids (RHA) and cochlear implants (CI) compensate the disability, but deficits in the receptive language abilities are still reported by patients, especially in an environment with a background noise. This impairment can lead to a decrease in daily activities and to social withdrawal. Here, we used Repetitive Transcranial Magnetic Stimulation (rTMS), a non-invasive brain stimulation (NIBS) technique used to promote cortical network plasticity, to improve speech perception in the post CI period. To this aim, we capitalized from the following evidences: i) rTMS has been already used in patients with sudden sensorineural HL for helping the recovery of hearing function and tinnitus; ii) we present here a study in which we have used rTMS of the auditory cortex to improve speech perception in background noise in 24 patients with removable hearing aids and chronic hearing loss; iii) we have verified the feasibility of rTMS in patients with CI that, according to currently available safety guidelines, cannot undergo rTMS treatment due to possible damage to implants caused by the TMS pulses. New generation CI - that resist to a static magnetic field, such as those of a magnetic resonance - might resist to pulses that vary rapidly, such as those of TMS. In a preliminary experiment, magnetocompatible CI were tested by repeated applications of rTMS protocols. Then, 9 CI patients underwent an active or a sham 5 days rTMS treatment delivered over the left auditory association cortex. In CI patients, rTMS was also followed by one hour of speech therapy (ST). Before (T0), after (T1), one week after (T2) and 6 months after (T3) the end of the treatment, Italian Matrix Sentence Test, Paced-Auditory-Serial-Addition-Test (PASAT) and speech tests were administered, with and without a background noise, in order to assess the patients’ speech-reception-threshold (SRT), verbal working memory and speech perception skills respectively. No damage was caused to the tested CI in the preliminary experiment. A significant long-lasting reduction of SRT was detected in RHA patients of the active group compared to the sham one. Moreover, a pattern of improvement in the SRT, in the working memory and in the speech perception was also detected in CI patients of the active group compared to the placebo treatment group. Results suggest that active rTMS might favour brain neuromodulatory changes in RHA and in CI patients, which are pivotal to the sounds and the speech intelligibility in the noisy environment daily-life.