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A major goal of neuroprosthetics is to design artificial limbs that are experienced (‘embodied’) like real limbs. However, despite important technological advances, this goal has not been reached and prosthesis embodiment is still very limited. Differently from our physical body, current bionic limbs do not provide the continuous multisensory feedback required for a limb to be experienced as one’s own. Here, we present a novel neuroprosthetic approach that combines peripheral neurotactile stimulation—inducing tactile sensation on the missing limb—and immersive digital technology—providing visual illumination of the prosthetic hand. We tested whether coherent multisensory visuo-tactile neural stimulation (VTNS)1 induced higher prosthesis embodiment and reduced the distorted perception of the phantom limb (telescoping, ie, the phantom limb is perceived as shorter than the intact limb).
Patient 1 and patient 2 are transradial left forearm chronic amputees, who suffered upper limb telescoping. Patients were implanted with transverse intrafascicular multichannel electrodes (TIMEs), which induced the sensation of a vibration in a circumscribed skin region of the finger 2 via medial nerve stimulation in patient 1 (online supplementary figure 1A) and in a skin region of finger 5 via ulnar nerve stimulation in patient 2 (online supplementary figure 1B and material 1). Neurotactile stimulation2 was coupled with automatised visual illumination of a skin region on the patient’s prosthetic hand that corresponded to the somatotopic location of touch sensations experienced on the phantom hand (VTNS; online supplementary video 1, online supplementary figure 1, online supplementary material 1). VTNS was administered in two conditions, either with synchronous visual and neurotactile stimulation or in a control condition of asynchronous stimulation (1.5–2.5s delay).
Prosthesis embodiment was measured via a questionnaire, whereas changes in phantom limb perception were tested via a body landmark task where patients indicated the perceived position of different parts of the phantom limb …
GR, FMP and SR contributed equally.
AS, SM and OB contributed equally.
Contributors GR designed the study, performed the experiments, analysed the data and wrote the paper. FMP and SR developed the software for the neural stimulation, contributed to the design of the study, performed the experiments and wrote the paper (GR, FMP and SR equally contributed to the work). GG, RDI, IS, GV and ED collaborated during the development of the neural stimulation software and during the experiment. MS designed, performed and analysed the telescoping experiment. RM developed the augmented reality software and integrated it with the neural stimulation device. JB-R and BH integrated the augmented reality software with the neural stimulation device, contributed to the design of the experiments and performed part of the experiments. GDP selected the patients and collaborated during the experiments. TS developed the TIME electrodes. DA and DG developed the device for the neural stimulation. PMR selected the patients and supervised the experiments. AS designed the study, performed the experiments, analysed the data and wrote the paper. SM and OB designed the study, supervised the experiments and wrote the paper (AS, SM and OB equally contributed to the work). All the authors read and approved the manuscript.
Funding This work was partly supported by the EU Grant CP-FP-INFSO 224012 TIME project (Transverse Intrafascicular Multichannel Electrode system), by the EU Grant FET 611687 NEBIAS Project (NEurocontrolled BIdirectional Artificial upper limb and hand prosthesiS), by the EU Grant Health 602547 EPIONE project (Natural sensory feedback for phantom limb pain modulation and therapy), by the EU Grant ERC-STG 678908 RESHAPE project, by the project NEMESIS (Neurocontrolled mechatronic hand prosthesis) funded by the Italian Ministry of Health, by the Bertarelli Foundation, by the Wyss Center for Bio and Neuro-engineering and by the Swiss National Competence Center in Research (NCCR) in Robotics.
Competing interests SM, SR, FMP hold shares of Sensars Neuroprosthetics, a company working to commercialise novel solutions for transradial amputees.
Patient consent Not required.
Ethics approval The experimental procedures were approved by both the Institutional Ethics Committees of Policlinic A Gemelli at Catholic University and the IRCCS S Raffaele Pisana (Rome). Informed consent was obtained from both patients.
Provenance and peer review Not commissioned; externally peer reviewed.
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