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By clinical observations of 115 centenarians and 742 nonagenarians, the actual state of mental aging of the very old Japanese and some factors relating to it are shown in this paper. A great difference in psychophysical functions was found between the centenarians and the nonagenarians. Most centenarians manifested a distinct decline in these functions, while a decline was less prominent in the 90-year-olds. There was a significant relationship between mental and physical functions. Those manifesting a prominent decline in intellectual ability showed more frequent reduction in physical ability as well, and vice versa. The degree of their intellectual ability was also related to the following factors: their sex, academic and occupational careers, some types of personality traits and personality changes. The mental decline was less prominent in males, in the educated and in those with a syntonic personality than in others.
Karasawa et al. (Sat,) studied this question.