Crossed Vestibular Connections in the Froc

Abstract

The crossed vestibular root to the area statica and reticular formation was investigated in frogs by the electrophysiological method. The area statica formed by the nucleus magnocellularis and ventral nucleus presented spontaneous activity, which increased in frequency and amplitude with both clockwise and counter-clockwise rotatory stimulation. In addition, the nucleus magnocellularis responded to acoustic stimuli. Labyrinthectomy carried out in several ways demonstrated that signals arising in one semicircular canal were transmitted to the area statica of both sides. An extensive area of the reticular formation of both sides exhibited spontaneous activity, which also increased in frequency and amplitude with both clockwise and counter-clockwise rotatory stimulation. The results showed that the signals from one lateral semicircular canal are transmitted to the reticular formation of both sides. The lateral ampullary nerve at rest exhibited spontaneous activity, which increased in frequency and amplitude with rotatory stimulation producing ampullopetal flow. When the stimulus produced ampulloiugal flow, the spontaneous activity diminished considerably or disappeared. The importance of these results for understanding the evolution of the vestibular system is discussed.