Strategies for restoring somatic sensations in upper-limb amputees through non-invasive methods

Nowadays, a large number of people suffers from limb amputation, which could be caused by several factors, such as traumatic events or as a consequence of serious inflammations. Therefore, it could severely affect the autonomy of a human being, by reducing his/her motor capabilities and sociability. For that reasons it should be relevant to find technological solutions able to reduce the gap between the people affected by an amputation and the society. Current solutions are represented by prosthetic device that are capable of replacing wholly, or in part, the residual limb. A particular focus is placed on the restoration of sensory feedback, as this has been identified as a highly desired additional feature for future prosthetic hand development. Promising results have been demonstrated for both invasive and non-invasive sensory feedback techniques, when the user was provided with central nervous system (CNS) or with the peripheral (PNS) neural interfaces. It is important to promote the development of innovative stimulation techniques based on non-invasive methods of interfacing with the nervous system, so as to increase user acceptability of the system and reduce its invasiveness. The aim of this thesis is to develop and validate novel sensory feedback stimulation methods based on non-invasive interfaces, aiming to improve the process for the restoration of the full spectrum of natural sensations. The study will focus on two promising non-invasive techniques: Transcutaneous Electrical Nerve Stimulation (TENS), which interfaces with the PNS, and transcranial Focused Ultrasound Stimulation (tFUS), which interfaces with the CNS. Research activities to pursue these objectives were focused on: (i) the development and validation of traditional encoding strategies to recreate force and slippage sensations in transradial amputees; (ii) the development and validation of novel bio-inspred strategies for encoding mechanoception, nociception and thermoception information in able-bodied subjects through TENS; (iii) the development of a neurocomputational model for simulating the effects of tFUS on cortical sensory structures in order to guide the application of safe and effective stimulations.