前庭眼反射における年令変化に関する研究
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The vestibulo-ocular reflex (VOR) helps to maintain a stable retinal image by generating compensatory eye movements so as to offset the effects of head rotation. The VOR gain in normal subjects in the dark is about 0.6 at a relatively low frequency range of pendular rotation. Recently, it has been reported that patients with cerebellar lesions such as cerebellar atrophy, in which the number of cerebellar neurons decreases, show high VOR agin compared to nomal subjects. In addition, it has been well-known that the population of cerebellar neurons gradually decreases with aging. From these, it is suspected that aging probably influences the VOR gain control. We examined the horizontal VOR gain in the dark at the frequency of 0.25Hz pendular rotation in each decade of age from zero, actually older than 5 years to the seventies, and also the adaptation of VOR gain to the horizontal vision reversal condition with right-left vision reversing prisms. The VOR gain in the dark was the lowest (0.59) in the subjects in their thirties and its gain gradually became higher with increasing age, for example 0.77 for those in their seventies. We found that in younger subjects the VOR gain was also very high compared to those in their twenties, thirties and forties. For example, in the youngest decade, i.e. from 5 to 9 years, the mean VOR gain was 0.84. The adaptation of VOR to reversing prisms, on the other hand, was not affected by aging.From these results, we speculate that the VOR gain in humans is probably highest in newborns. In human life, this high VOR gain produces plastic changes (learning) because visual and vestibular inputs often conflict with each other. The high VOR gain in older subjects reflects the reduction of the inhibitory activity to the VOR arc from the cerebellar Purkinje cells due to the decrease in the population of neurons brought about by aging. Thus, we speculate that in the younger age the learning effect is predominant compared with the aging effect and in the older age the aging effect is predominant compared with the learning effect.
- 耳鼻咽喉科臨床学会の論文
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