Vestibular and optokinetic evoked potentials.

Earlier studies of vestibular evoked potentials have adopted the expedient of rotating subjects with eyes closed and in consequences there exists a suspicion that the responses obtained might have been contaminated by corneo-retinal potentials. In order to minimise this artefact, subjects were required to fixate upon a small target light attached to and rotating with the chair while in total darkness. The rotational stimulus was a controlled angular rotation of the chair simulating a normal head movement. Averaged responses of ten such stimuli have revealed a consistent and well defined characteristic wave form not present in six patients with total vestibular loss. Similar evoked responses were obtained to a full field optokinetic stimulus approximating to that of the movement of the chair. Combined optokinetic and vestibular stimulation does not show algebraic summation. The evoked responses have features in common with nervous activity recorded in the monkey at vestibular nuclei and thalamic levels in comparable test situations.