Exploring Training Methods for Dissociating Muscle Activity in Arm Prosthesis Control Applications

Abstract

The level of motor skills regain of an arm prosthesis wearer is directly related to the precision and reliability with which he can select, initiate, guide, and terminate the movements of the mechanism with appropriate control musculature. To develop the necessary control skills, special muscle training is necessary. Utilization of any muscle in the shoulder girdle or general trunk region depends on its dissociation from group action in order to achieve isolated function since such muscles normally are used only in coordinated group activity. The following conditions must be met to achieve voluntary control over the contraction of a selected muscle: ( a ) facilitation of contraction and simultaneous inhibition of activity in synergsts and/or antagonists; ( b ) inhibition of conuaction during activity in synergists and/or antagonists; and ( c ) graded control over contraction and relaxation. One approach to meet these requirements was to utilize the concept of non-plasticity of the mature CNS (Sperry, 1943). Motor denervation of a muscle and its re-innervation with a nerve which formerly carried functional messages as, for example, lift forearm, seemed to provide a means for associating voluntary initiation of muscle contraction with a prosthetically meaningful movement. To this end, the following pilot experiment was conducted on two monkeys. Monkey A, a male Macaca mulatta (rhesus monkey) who was born in the UCLA vivarium in 1957, was two yr. old at the time of surgery and weighed 3.4 kg. Monkey B was a female Cyne malagus who was captured in the jungles of Borneo and shipped to UCLA in 1959 at an approximate age of 2 years. The animal was about 2Y2 years old at the time of surgery and weighed 3.7 kg. A branch of the musculocutaneous nerve supplying the right biceps was transferred and anastomosed to the proximal stump of the severed medial and anterior thoracic nerves. EMG records were obtained ac intervals over a period of approximately 12 months. Slight pectoralis contraction became evident six months postoperatively and gradually increased to normal suength in both animals. Monkey B showed the expected synchronous discharge patterns in right