Association between pupillary unrest index and waking electroencephalogram activity in sleep-deprived healthy adults

In recent years there has been growing interest in the use of pupillography as an objective and time-saving method to assess the level of sleepiness. The aim of our study was to further elucidate the validity of pupillography by investigating the association of pupillometric variables with subjective sleepiness and waking electroencephalogram (EEG) activity.

The level of sleepiness of 24 young healthy adults was evaluated during 40h of sustained wakefulness using pupillography and subjective ratings with the Stanford sleepiness scale and a visual analog scale (VAS). During the assessment of sleepiness by pupillography, waking EEG was simultaneously recorded and subjected to spectral analyses. As a pupillographic measure of sleepiness the pupillary unrest index (PUI) was calculated.

PUI, subjective sleepiness, and power in the δ, θ, α1, β1, and β3 frequency band exhibited significant variations over time. PUI showed a prominent circadian modulation under high homeostatic sleep pressure. At time points of maximum PUI indicating a high level of sleepiness, significant increases were found in subjective sleepiness as well as in δ, θ, α1, and β1 power. Moreover, PUI showed a significant, high intraindividual correlation with subjective sleepiness and with power in the δ, θ, and α1 frequency band.

The novel finding of a close association between pupillometric variables and distinct changes in waking EEG activity underscores the validity of pupillography as a time- and cost-efficient objective measure of sleepiness that could ease the diagnostic and therapeutic workup of patients who report excessive daytime sleepiness.