Vibro tactile stimulation as a treatment for the voice disorder spasmodic dysphonia

Abstract

Spasmodic dysphonia (SD) is rare focal dystonia affecting the laryngeal musculature. Patients with SD typically experience a strained or choked speech and report that it takes an exhausting effort for them to speak. The disorder develops spontaneously during midlife. Its progression is gradual in the first year and then becomes chronic for life. At present, there is no cure for SD and it is unresponsive to behavioral speech therapy. It is treated primarily with Botulinum toxin (Botox) injections for temporary symptom relief. Proprioceptive deficits are an underlying feature of SD - a finding that opens an avenue for a missing behavioral treatment for the disease. Specifically, vibro-tactile stimulation (VTS) could be the suitable tool, given that it alters afferent signals from the mechanoreceptors in the vibrated muscles and skin.This cumulative dissertation concerns a non-invasive neuromodulation approach using VTS for treating the voice symptoms in people with SD. It consists of three separate projects. The first project examined the short-term effect of vibro-tactile stimulation (VTS) on speech quality and cortical activity of 12 participants with adductor SD and one with abductor SD. The results showed that 9 participants (69%) exhibited a reduction of voice breaks and/or a meaningful increase in smoothed cepstral peak prominence, an acoustic measure of voice/speech quality. Symptom improvements persisted for 20 minutes past VTS. In addition, VTS induced a significant suppression of theta band power over the left somatosensory-motor cortex and a significant rise of gamma rhythm over the right somatosensory-motor cortex. Our results show convincingly that VTS represents a non-invasive form of neuromodulation that induces measurable short-term improvements in patients' speech with adductor SD. The second project represents a logical step to expand on the previous work to improve VTS technology and make it wearable. To that effect, I have designed and developed a wearable non-invasive collar-like device that applies VTS to the laryngeal muscles. The device provides two operational modes, continuous VTS and real-time VTS, using a developed speech detection technology. The speech detection algorithm allows for individualized system calibration providing flexibility in adjusting the device for users with different anatomy and/or disease severity. For the final project, I used the device that was developed in project 2 to examine the efficacy of VTS for treating voice symptoms in people with abductor SD. The results showed an improvement in at least one marker of voice quality for 3 out of 4 participants. The improvement lasted for 20 and 60 minutes after cessation of VTS for one participant. However, we require a larger sample to have a confident response rate to the laryngeal VTS in AB SD. The current analysis of electrocortical responses to VTS in people with AB SD did not closely mimic the event -elated cortical activity patterns seen in AD SD. More data are needed to delineate consistent patterns of cortical responses induced by laryngeal VTS in AB SD.