Neurological pupillary noise in narcolepsy

Pupillometry has a long but inconclusive history as a means of measuring human alertness. Spontaneous pupillary oscillations in narcoleptics and the sleep deprived are a recognized but quantitatively elusive indication of alertness. Stimulation of the pupillary light reflex (PLR) has provided contradictory or confusion indications of alertness levels. Results from 10 diagnosed narcoleptics and 10 control subjects in which the PLR system was stimulated and a reliable (90%) discriminator derived for classifying narcoleptics and controls was reported. Random pupillary oscillations, which is called pupillary noise to distinguish these oscillations from spontaneous ones, were estimated from continuous pupil diameter recordings using a recursive least squares method applied to a subject-specific PLR system model. Pupillary noise sum of squares indicate that narcoleptics have significantly (P < 0.005) less PLR noise than controls. This difference was attributed to supranuclear inhibition of randomly active Edinger-Westphal neurons long hypothesized to be the source of random pupillary oscillations. This inhibition also has been suggested as a cause of PLR sensitivity to nocturnal sleep quality so it may be that these findings apply to the sleep deprived and not just specifically to narcoleptics.