Responses of oculomotor units to stimulation of single semicircular canals

Abstract

Extracellular recording of the electrical activity of the oculomotor nuclei was carried out in paralyzed guinea pigs by means of tungsten microelectrodes. The influence of each one of the three semicircular canals of one side on such unitary discharge was studied. Labyrinthine stimulation was carried out by short-lasting (1–2 sec) localized warming or cooling of each single semicircular osseous canal. All the recorded oculomotor units underwent modifications. These consisted either of rhythmical (slow or quick) responses or of a long-lasting increase in the discharge rate of the units with recruitment of new units without clear signs of rhythm (continuous activation). In about 40% of the experiments the recorded units responded differently to the warm stimulation of each semicircular canal, while in the remaining 60% of the case two out of three canals elicited the same type of response. In the great majority of the experiments the warm stimulation of the lateral ampulla induced a type of response different from that provoked by stimulating the superior one.