Neural Plasticity and Repair in Rehabilitation

Scientific progress in understanding the cellular and molecular responsesof the central nervous system (CNS) to injury has expanded the focus of neurorehabilitation beyond the traditional boundaries of behavioral adaptation, emotional support, and mechanical prosthetic and orthotic devices. Neurorehabilitation is now attempting to manipulate the intrinsic plasticity of the CNS and to harness it in the interests of functional recovery. This constitutes a profound advance that permits the field of neurorehabilitation to aspire to cure patients whose physiological impairments heretofore were considered fixed. It is this exciting enlargement in the scope of research and clinical practice that inspired the change in the name of this journal from the Journal of Neurorehabilitation to Neurorehabilitation and Neural Repair, beginning with Volume 13 in 1999. A recent issue of this journal (Vol. 13, Issue 3) focused on one aspect of the new emphasis on neural plasticity (i.e., the attempt to enhance the strength of the output of the human central pattern generator for locomotion through partial body weight-supported treadmill training). The rationale for this approach is the evidence that the neural circuitry constituting the central pattern generator is subject to use-dependent modifications that can result in motor learning (1). The articles in the present issue of Neurorehabilitation and Neural Repair highlight additional properties of the nervous system that permit it to undergo repair and reorganization so as to compensate for neural injury or damage by disease. The issue is led off by a special feature of this journal, Reviews in Neurorehabilitation Therapeutics. The subject addressed by Gorman (2), functional electrical stimulation (FES), bridges traditional rehabilitation techniques and the approaches to neural repair addressed by the other articles. After years of holding out promise for assisting neurologically impaired patients, FES has been applied to solving practical problems, including loss of cardiovascular exercise, bladder control, ejaculation, hand grasping, respiratory drive, standing, and walking. Eight devices applied to seven functions have already been approved by the Food and Drug Administration (FDA) for use in spinal cord-injured patients. As Gorman points out, for reasons of stimulus-intensity threshold and other practical limitations, FES devices actually stimulate axons, not muscles directly. The consequence of this is that the approaches reviewed in his article pertain to muscles that have lost supraspinal control, and not to those that have lost lower motor neuron innervation, as for example at the level of spinal cord injury. Although the functional restoration achieved by the current generation of FESdevices is in many cases still quite primitive, there is every indication that their sophistication and practical usefulness will continue to increase. Because most of these devices must be activated by the patient by using surrogate neural instructions, they interface with the patients' own motor learning and neural plasticity. In this respect, today's FESdevices are forerunners of more sophisticated neural prostheses already under development (e.g., replacement retinal circuitry), which may be able to substitute for lost neural circuits and reconnect parts of the CNS not only with peripheral nerves and muscles, but also with other parts of the CNS from which they had been disconnected by injury and disease. It is entirely possible that in the future, neural repair will use combinations of microelectronic and biologic neural prostheses. Two articles explore concepts of cortical reorganization associated with phantom limb phenomena. The first is a single case of leg amputation reported by Maruno et al. (3). As expected, actual movement of the toes on the unamputated side was associated with activation of the primary motor cortex, the primary sensorycortex, and the supplementary motor area of the contralateral side on functional magnetic resonance imaging (fMRI). Consis-