Many amputees suffer from Phantom Limb Pain (PLP), a condition where painful perceptions arise from the missing limb. Leg amputees wear prostheses that do not provide any sensory feedback, apart from the stump-socket interaction. Increased physical effort associated with prosthesis use as well as discomfort often lead to rejection of artificial limbs. Additionally, the perception of the missing limb and its brain representation, do not match-up with what amputees see (the prosthesis) and this is made worse by the absence of sensory feedback. Therefore, re-establishing the sensory flow of information between the subject's brain and the prosthetic device is extremely important to avoid this mismatch, which creates inadequate embodiment. This study focuses on improving functional abilities and decreasing PLP in amputees thanks to the use of a system able to generate a sensory feedback (SF), which will be provided with a non-invasive electrical stimulation (ES). First, the possibility of enhancing the performance in different functional tasks thanks to the use of SF will be explored. Furthermore, it will be evaluated if SF enhances the prosthesis embodiment and helps restoring a multisensory integration (visuo-tactile), potentially providing also a pain relief. Once tested this system on amputees, also people with peripheral neuropathy and sensory loss will be recruited. Diabetic patients can suffer from symmetrical polyneuropathy (DSPN), which is a common complication caused by prolonged glucose unbalanced levels that lead to nerve damage. Non-invasive ES has been proposed and used as a therapy to treat the chronic pain conditions. In particular, TENS (transcutaneous electrical nerve stimulation) is a type of non-invasive ES, which is able to activate large diameter afferent fibers. The gate control theory of pain states that these large diameter fibers inhibit central nociceptive transmission with a resultant decrease in pain perception. Therefore, also these patients will be recruited to see whether adding a non-invasive SF can enhance their functional motor abilities while diminishing their pain.

The subjects will perform a pool of the following tasks, depending on their residual abilities: motor tasks (walking on ground level and on stairs), cognitive tasks (dual tasks), subjective evaluation of prosthesis weight and description of sensations from ES.

Some tasks will be performed in Virtual Reality environments with and without an active stimulation.

Inclusion Criteria:

• transfemoral amputation or transtibial amputation or knee disarticulation or diabetic peripheral neuropathy
• the subject should be healthy other than the amputation and the diabetic neuropathy and in the range of 18-70 years old
• the subject should be able to comfortably walk, sit and stand alone

Exclusion Criteria:

• cognitive impairment
• pregnancy
• Prior or current psychological diseases such as borderline, schizophrenia, Depression or Maniac Depression
• acquired brain injury with residual impairment
• excessive sensitivity or pain to electrical stimulation with surface electrodes
• cybersickness