Postural and oculomotor signs in labyrinthine-defective subjects

Bilabyrinthless subjects, i.e. subjects clinically devoid of labyrinthine responses, show a greater than normal decrease in postural stability following eye closure. Because changes in head position, which affect posture in healthy subjects, do not do so in bilabyrinthless patients, static afferent information from healthy neck receptors does not contribute to postural stabilization. Somatosensory nystagmus and dynamic cervico-ocular responses are equally greater in bilabyrinthless than normal subjects, which indicates that both categories of eye movements are mediated by the same mechanism. Optokinetic nystagmus is slightly diminished in bilabyrinthless patients and optokinetic after-nystagmus was mostly absent. In terms of the Raphan-Cohen model our findings confirm that destruction of the labyrinthine function abolishes the vestibulo-ocular integrator function.