Effects of calorizations and repeated unidirectional angular accelerations on the nystagmus of unilaterally labyrinthectomized cats.

Right unilateral labyrinthectomy of cats resulted in a left-beating, spontaneous nystagmus that was still weakly present in most animals when recorded in darkness 2 months after surgery. Cats given cold calorizations of the non-operated ear during the month following surgery showed no differences in behavior, optokinetic nystagmus, spontaneous nystagmus, or rotation-induced nystagmus when compared with operated cats which received no caloric stimulation. All operated cats showed a reduction in optokinetic responses that was more marked to CCW stimulus and that persisted through the second month after surgery. Most nystagmic responses to angular accelerations were bidirectionally diminished by more than 50%, 1 month after surgery. A series of 15 unidirectional habituation trials was ineffective in producing a directional imbalance in the nystagmic responses of operated cats, but the series was effective with non-operated Control animals. It appears that an intact vestibular system may be necessary for directionally specific habituation effects to evidence themselves. One month after the habituation series, all operated cats showed improved nystagmic output while Control cats showed a trend toward equalization of responses for the two directions.