Neurological pupillary noise in narcolepsy

Area of Science:

• Neuroscience
• Ophthalmology
• Sleep Medicine

Background:

• Pupillometry has a long history of attempting to measure human alertness, but results have been inconclusive.
• Spontaneous pupillary oscillations and pupillary light reflex (PLR) stimulation have yielded confusing or contradictory indications of alertness.
• Narcolepsy and sleep deprivation are known to affect alertness, but objective quantitative measures remain elusive.

Purpose of the Study:

• To investigate pupillometry as a reliable method for measuring alertness in narcolepsy.
• To derive a quantitative discriminator for classifying narcoleptics and controls using pupillary measurements.
• To explore the relationship between pupillary noise and the Edinger-Westphal neurons' activity.

Main Methods:

• Continuous pupil diameter recordings were obtained from 10 narcoleptic and 10 control subjects.
• A recursive least squares method was applied to a subject-specific pupillary light reflex (PLR) system model to estimate pupillary noise.
• The sum of squares of pupillary noise was calculated to quantify differences between groups.

Main Results:

• Narcoleptics demonstrated significantly less pupillary noise (P < 0.005) compared to control subjects.
• A reliable (90%) discriminator was derived for classifying narcoleptics and controls based on pupillary noise.
• Reduced pupillary noise in narcoleptics was attributed to supranuclear inhibition of Edinger-Westphal neurons.

Conclusions:

• Pupillometry, specifically the measurement of pupillary noise, offers a reliable method for distinguishing narcoleptics from controls.
• The findings suggest that reduced pupillary noise may be linked to supranuclear inhibition affecting alertness.
• These results may also be applicable to understanding alertness in the sleep-deprived population, not just narcoleptics.