Ocular Electromyography in Brain Stem Dysfunction

Abstract

The purpose of this paper is to show how electromyography (EMG) of the eye muscles serves to elucidate physiologic phenomena occurring in the presence of brain stem dysfunction.One of the basic tenets of ocular muscle physiology is that excitation of one set of muscles (agonists) is associated with the inhibition of the opposing set (antagonists), exemplified both ipsilaterally and contralaterally. Electromyography affords an opportunity to demonstrate these basic phenomena not only in the course of normal eye movements but also in conjugate and disconjugate gaze disorders and even, as in this case, in apparent (clinical) paralysis of eye movement. While many descriptions of ocular motor disorders are available, most reports discuss the defects in eye movement without specifically alluding to excitation or, in particular, to inhibition. This report will emphasize these phenomena and the correlation of clinical and electromyographic findings.From the electrophysiologic point of view, one of the striking characteristics of ocular muscles is the presence of "tonic activity" (or evidence of continuous electrical excita¬ tion to the eye muscles) when the eyes appear to be "resting" in the midposition in an alert subject. Peripheral skeletal mus¬ cle "at rest" will have no recordable electrical activity. Complete electrical si-