Vertical nystagmus provoked by locally applied calorization at the vertical semicircular canals: a study in pigeons

Calorization of the vertical semicircular canals in pigeons was performed by irrigation of water through a polyethylene cannula, that was attached at a selected site to the bony wall of the anterior or posterior canal of the labyrinth. The temperature differences between the stimulated site and the corresponding location inside the contralateral mastoid were detected by two thermistors. (a) Calorization of an anterior or posterior canal evoked a dissociated vertical nystagmus in both eyes. (b) The direction of the nystagmus and of the vertical slow phase velocity proved to be temperature-dependent. (c) The vertical eye movements disappeared when the stimulated canal was placed horizontally during calorization. (d) During parabolic flight the vertical and horizontal eye movements, elicited by sustained calorization, disappeared during short periods of microgravity and proved to be dependent to the g load. (e) All vertical canal calorizations evoked eye movements in the plane parallel to the stimulated canal. Left and right eye moved in opposite vertical directions, depending on the selected site of calorization on the vertical canal. (f) The same mode (warm or cold) of calorization of an anterior canal provoked similar vertical movements of both eyes as compared to the vertical eye movements that were induced by calorization of the contralateral posterior canal. The results are discussed in view of the 'convection current' and the 'expansion/contraction' theory and they are compared to previously reported results of vestibular nerve stimulation.