Habituation, Efference and Vestibular Interplay I.:Monaural Caloric Habituation

Abstract

Monaural habituation was produced in twelve subjects by repeated hot-water irrigation, and in twelve others by cold-water irrigation. Two different groups of results were obtained. Group 1 exhibited directional preponderance towards the contralateral ear after hot-water habituation and towards the ipsilateral ear after cold-water habituation. Group 2 showed a reduced duration of nystagmus after both hot-water and cold-water irrigation of both ears. The group 1 results were attributed primarily to a modified efferent activity elicited from the reticular formation, and secondarily to a change in the reciprocal activity of the two labyrinths. The responses in group 2, on the other hand, were ascribed to a more pronounced effect on the reticular formation, which thus modified the activity of the intervestibular communication. During the course of habituation tests several of the subjects developed secondary nystagmus, and two of them even spontaneous nystagmus. This is accounted for by the assumption that habituation disrupts the balanced activity of the two vestibular apparatuses, the disproportion reaching, in maximal cases, the threshold for spontaneous nystagmus. Several instances of dysrhythmia were also observed and may be attributable partly to disproportion as above and partly to fluctuations of activity in higher and lower centers. The reasons underlying this theory are discussed. Since the dysrhythmia impedes evaluation of the results from the velocity of the slow phase, the duration of nystagmus remains as the only reliable mathematical criterion of the response from the peripheral labyrinth.