Ultradian rhythms in alertness - a pupillometric study.

Pupillary size, pupillary light reflex and pupillary motility were measured every 15 min, for 10 continuous hours, in eight young adults. Time series constructed from the range of pupillary motility revealed 75 to 125 min rhythms; these were significantly out of phase with rhythms of similar periodicity in pupillary diameter and in the magnitude of the pupillary light reflex. There was no consistent correspondence between Stanford Sleepiness Scores and pupillary activity. It is suggested that the rhythms in pupillary activity reflect underlying rhythms in CNS arousal that also modulate perceptual, cognitive and electroencephalographic processes, a conclusion which supports Kleitman's BRAC model.