Habituation, Efference and Vestibular Interplay:IV. Rotatory habituation of the vertical semicircular canals

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Abstract
Twenty-two persons were subjected to rotary habituation of the vertical semicircular canals. The posterior canals were habituated in 12 subjects and the anterior canals in 10. Initially tests were made of the post-rotatory nystagmus duration in both directions. Thereafter the patients were rotated in the same direction 12-16 times. Finally a fresh post-rotatory test was made and the values were compared with the initial values. After the habituation of the posterior canals there was obtained in two subjects a directional preponderance downwards, while nine subjects had reduced reactions in both nystagmus directions. One subject had primarily a nystagmus upwards which increased somewhat in intensity after habituation. Habituation of the anterior vertical semicircular canal gave eight cases which had directional preponderance upwards, two even spontaneous nystagmus upwards, while two persons had reduced reactions in both nystagmus directions. All of the eight subjects who did not get spontaneous nystagmus had instead a secondary nystagmus upwards. The results show that the vertical canals react differently from the horizontal canals and that they also react differently among themselves upon habituation. Various explanations of this are discussed.