Modification of the Electromyogram of the Simple Reaction by Cerebellar Lesions

When simple quick voluntary movements are studied by a combination of action potential and gross movement technics, the contraction of the muscles, and the gross movements occur in a fairly definite sequence. Though finer details vary widely among normals, there are fairly constant gross characteristics. 1 If antagonistic striated muscles are recorded, it will be seen that they will both show potentials within an average time of about 9_σ from one another. The contraction potentials of the muscle which will shorten in the response occur slightly ahead of its antagonist. The acting muscle will also contract more strongly than the antagonistic muscle though this difference is not always easily observable on action potential records. At a period of about 60 to 100_σ after the appearance of the initial contraction in the muscle, the gross movement begins. (Fig. 1.) These statements are not in accord with the current concepts of the lengthening reaction in antagonistic muscles, but they do substantiate the results of Tilney and Pike 2 who studied this question mainly from the standpoint of muscle volume changes in voluntary movement. Weisenburg 3 has said, “If there is a lesion in any part of the cerebellar apparatus there is necessarily produced a disturbance or destruction of the association between agonists and antagonists, and the resulting movement must necessarily be incoordinate or asynergic.”

Since we had studied the coordination of simple extension or flexion by the paired action of the triceps and biceps brachii, and to a lesser degree the quadriceps femoris and hamstring group, it seemed advisable to study this response in cases with cerebellar lesions.

The subject was placed in a comfortable position with the forearm supported so that it could rotate freely in a horizontal plane about the elbow. He was instructed to extend (or flex) the forearm as quickly as he could after the appearance of a light which was used for a stimulus. The same technic was used for the extension of the lower leg at the knee joint except that in this case no support was used, the lower leg being simply kicked forward. These movements were practiced before the pictures were actually taken. The records show the action potentials in the muscles involved, the gross movement, the point of appearance of the signal, and a time line for reading the time differences involved. The slope of the gross movement line is an approximate value for the force of the movement.