A blind individual living in normal society can exhibit a free-running circadian rhythm of 24.9 hours, leading to severe cyclic sleep-wake disorder.
A psychologically normal blind man, living and working in normal society, suffered from a severe cyclic sleep-wake disorder. Investigations showed that he had circadian rhythms of body temperature, alertness, performance, cortisol secretion, and urinary electrolyte excretion which were desynchronized from the 24-hour societal schedule. These rhythms all had periods which were longer than 24 hours and indistinguishable from the period of the lunar day.
Miles et al. (Fri,) studied this question.
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