The maintenance of a standing posture and balance recovery in response to perturbation are important and remarkably complex skills which require the integration of visual, vestibular, and somatosensory inputs. While these three systems provide distinctly different types of information, the high degree of integration in the central nervous system renders prediction of the effects of removal or degradation of any one channel difficult. The somatosensory system carries the important responsibility of providing proprioception, exteroception, and kinesthesia from the periphery to the spinal and supra-spinal levels. There is an ongoing debate in the literature concerning the relative importance of somatosensory afferent information and centrally stored motor plans in the initiation and control of complex movements. This debate exists because no readily available model exists to isolate the effects of peripheral sensation although much important work to elucidate the mechanisms of postural control has been performed with healthy human subjects using a variety of creative interventions and experimental conditions to induce sensory deficits.Among the approaches used have been cooling of the feet, anesthesia of the pedal nerves, occlusion of blood supply to the limb, standing on foam, and vibration of tendons and muscles.While these experiments have led to theories concerning the role of somatosensory information in postural control, each of these models suffers from limitations. The applicants, therefore, propose to use the neuropathic diabetic model to investigate performance when somatosensory function is reduced. Clinically apparent peripheral nerve damage may occur in up to 25% of patients with diabetes mellitus after 10 years and, with rigorous screening and exclusion criteria, it is possible to identify individuals with predominantly sensory deficits and no other coexisting conditions that would affect posture. After establishing baseline values in a young healthy group of subjects, the experimental plan proposes to assemble a group of sixty diabetic patients between the ages of 40 and 70 who will have specific combinations of deficits in the plantar cutaneous and ankle joint receptors. Age-matched diabetic and non-diabetic control groups, with absent or mild neuropathy will also be studied. All subjects will have to meet strict inclusion criteria. Surface electromyograms, ground reaction forces, and joint kinematic measures will be recorded during a variety of challenges to upright posture. The study design is intended to allow the specific contributions of different components of the somatosensory system to postural control to be examined.
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