Investigators: Jessica Rose Agramonte, PhD, PT and Kevin C. McGill, PhD Project Staff: Zoia C. Lateva, PhD Project Category: Other - 2000 The purpose of this research is to characterize motor-unit firing behavior associated with the movement deficits of persons with upper motor neuron lesions. This study is specifically concerned with spastic cerebral palsy (CP), although the methods and interpretations are also applicable to stroke. Previous experimental evidence suggests that in CP there may be a reduction in motor-unit firing rates, presumably as a result of the interrupted descending signals. Inability to increase firing rates sufficiently during contraction could cause weakness and loss of dexterity as is typically seen in both agonist and antagonist muscles in CP. In the ankle, for example, failure to generate adequate firing rates during voluntary phasic contraction could cause inadequate push off and toe clearance in gait and thus could be a primary cause of equinus gait in CP. For persons with CP, a failure to generate adequate firing rates during contraction may be amenable to treatment. There is early evidence to suggest that electrical stimulation to the calf and tibialis anterior may increase muscle strength, reduce calf spasticity, and improve equinus gait. Selective electrical intervention could improve motor control without causing the weakness or sedation that is characteristic of current pharmaceutical and surgical treatments for CP. An essential first step towards designing an effective treatment is a clear understanding of the mechanisms underlying the movement deficit. The specific aim of this study is to determine the feasibility of evaluating motor-unit firing properties in the gastrocnemius and tibialis anterior muscles in persons with spastic CP. The protocol compares firing characteristics at progressively increasing levels of voluntary contraction in subjects with CP and in matched controls to distinguish differences in motor-unit activation strategies. Based on these preliminary data, a full research proposal will be developed to investigate the relationship between muscle structure, motor unit firing behavior and motor deficit including gait kinematics in patients with CP. This research is envisioned to provide a foundation for the development of selective electrical treatment that could improve motor control in patients with spastic CP. Findings to Date: Five subjects with CP and seven control subjects have been tested. Intramuscular EMG signals were recorded separately during each contraction from two fine-wire electrodes inserted into different parts of each muscle. These signals were decomposed into individual motor-unit action potential trains using software we have developed, yielding from ten to thirty motor-unit trains per muscle per subject. Thus the feasibility of this approach has thus been demonstrated. Analysis of the firing characteristics is currently underway. Funding Source: NIH |
