Further Remarks on Nystagmic Responses due to Torsion of the Neck (Neck-Torsion Nystagmus)

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  • けいねん転頭位で誘発される正常ウサギの眼球運動　その成因に関する研究補遺
  • ケイネンテン トウイ デ ユウハツサレル セイジョウ ウサギ ノ ガンキュウ

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To obtain a better understanding of the characteristic of neck-torsion nystagmus previously reported (Ito and Hinoki 1980) the following experiments were undertaken using the normal rabbits with black eyes. Eye movements were observed using the electronystagmograph (ENG) and were examined in the following four postures. Some of the animals were examined using the electroencephalograph (EEG), together with the ENG. The results obtained were as follows:<br>(1) The posture used herein were:<br>(i) A posture in which a rabbit's trunk is hung and fixed with cloth and the four limbs are unrestrained. The head of the animal maintains a normal position with an anterior inclination of 45 degrees. (hereafter termed the 1st posture) (ii) A posture in which the animal maintains the left lateral decubitus without any sign of torsion of the neck. (hereafter termed the 2nd posture) (iii) A posture in which the animal takes the 2nd posture for at least 20 seconds and then the trunk is counterclockwise rotated at 90 degrees about the fixed head and hung after the same manner as mentioned in (i). (hereafter termed the 3rd posture) and (iv) A posture in which the animal's head maintains the above mentioned normal position. The trunk is then counterclockwise rotated around the longitudinal axis at more than 90 degrees. Thus, the four limbs of the animal points upwards. (hereafter termed the 4th posture)<br>(2) In the second posture the animal usually showed deviation of the eyes alone. Some of the animals showed nystagmic responses in this posture. However, such nystagmic responses were sporadic and did not show any constant reappearance. In contrast, the animal constantly showed regular and active nystagmic responses in the 3rd posture. The animal also showed nystagmic responses when the 4th posture was taken. However, such nystagmic responses were less obvious in frequency and amplitude as compared to those in the 3rd posture.<br>(3) There was a close relationship between the appearance of the nystagmic responses and the arousal state in the EEG.<br>(4) The nystagmic responses referred to herein showed a phenomenon of “Response Decline” even in the 3rd posture when the examination was repeated for a fairly long time and with a short rest. Such phenomenon was accompanied by the reduced activity of the EEG's. From these findings the following conclusions were drawn.<br>(a) The idea that the neck-torsion nystagmus previously reported is induced from the cervical proprioceptors in close collaboration with the otolithic organ of the peripheral labyrinth is supported by the present experiments.<br>(b) The appearance and decrease of the neck-torsion nystagmus are closely concerned with the activity of the brain, particularly the activity of the brain stem reticular formation.

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