Yutaka Oouchida

<p>Almost all the amputees feel the existence of the amputated limb after limb amputation, which is known to be phantom limb. Many amputees can move and control their phantom limb at their will and they report that they receive sensory feedback of the phantom limb while phantom limb moving. Further, approximately 50–80% of them have pain on the amputated limb, phantom limb pain. A possible mechanism for phantom limb is that the information of the body in the amputee's brain is not updated after amputation for some reason, causing this illusory feeling of the amputated limb. This phenomenon suggests that our body perception depends largely on the body information in the brain formed from sensory information of multimodal sensors in the body. For understanding the mechanism of our perceptual system, to examine the mismatch between actual sensory information in the environment and our perception is very useful. Thus, to elucidate the phantom limb will provide us with rich information to help understand the mechanism of our body perception.</p>

<p>&ensp;&ensp;It is well known that patients with chronic hemiplegia following brain damage often face difficulties in improving motor function, owing to maladaptive changes to cortical representation of the affected limbs. However, frequent training of paretic limbs enlarges their cortical representation by use-dependent plastic ity. Nevertheless, these processes interact to produce a downward learning, providing negative feedback from paretic limbs, which results in further 'learned nonuse'. This sensory disturbance leads to a gradual alteration of the representation of the body in the brain;consequently, there is a failure to generate efficient motor output.<br>&ensp;&ensp;This review describes several kinds of treatment to break this negative loop and to overcome this learned nonuse phenomenon underlying a number of disorders of body representation related to sensory and motor impairment using non-invasive techniques, boosting their multisensory capabilities, weakened by brain damage. We also introduce the effects of illusory ownership, the conscious experience of altered internal body representation induced by patterns of multisensory stimulation, on imitative movement performed by participants from a first-person perspective just after experiencing the crossmodal illusion as an example of therapeutic applications. These clinical applications illustrate the potential of neurorehabilitation for restor ing the maladaptive alterations of body representation corresponding to decreased frequency of usage caused by damage of peripheral or central nervous system.</p>