Delivering Speech by Non-Invasive Electric Stimulation of the Central Nervous System

Abstract

Recent advances in neuroscience and precise electric stimulation have enabled us to deliver complex signals to the central nervous system. But most of the successful electric stimulation devices such as cochlear implant and deep brain stimulation require surgery. Considering that most of the patients with hearing loss have a significant residual hearing, it is not feasible to open up the round window and insert an electrode in a functional cochlea. The concept of non-invasive electric stimulation of the auditory system may have a role in the future to overcome this unmet need in the clinic. Until now, many researchers have tried to delivery speech signal to the brain by means of non-invasive electric stimulation. Trans-cranial electric stimulation have most extensively been studied and interesting outcomes have recently been published. Some studied were able to prove that the envelope of the speech can be delivered by non-invasive electric stimulation. This new technology is called speech entrainment. By inducing speech entrainment, researchers were able to enhance the speech recognition score in noisy environments. But there are also some limitations in this approach. For instance, the time delay of the auditory sound and brain entrainment must be matched which is quite challenging. Although some limitation needs to be resolved, recent advancements in this new field is very interesting. More developments will follow in the next few years that can help patients with hearing loss in the near future.