Steady-State Pupil Size Varies with Circadian Phase and Sleep Homeostasis in Healthy Young Men.

Maxime Van Egroo,Giulia Gaggioni,Gilles Vandewalle,Julien Q M Ly,Cristian Cespedes-Ortiz

doi:10.3390/clockssleep1020021

Maxime Van Egroo, Giulia Gaggioni + Show 3 more

Open Access

https://doi.org/10.3390/clockssleep1020021

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Journal: Clocks & sleep	Publication Date: May 10, 2019
Citations: 11	License type: CC BY 4.0

Affiliation: University of Liège

Abstract

Pupil size informs about sympathovagal balance as well as cognitive and affective processes, and perception. It is also directly linked to phasic activity of the brainstem locus coeruleus, so that pupil measures have gained recent attention. Steady-state pupil size and its variability have been directly linked to sleep homeostasis and circadian phase, but results have been inconsistent. Here, we report robust changes in steady-state pupil size during 29 h of continuous wakefulness in healthy young men (N = 20; 18–30 years old) maintained in dim-light in strictly controlled constant routine conditions. These variations were associated with variations in motivation and sustained attention performance. Pupil size variability did not significantly change during the protocol. Yet, pupil size variability was linearly associated with subjective fatigue, sociability, and anguish. No associations were found between neither steady-state pupil size nor pupil size variability, and objective EEG measure of alertness and subjective sleepiness. Our data support therefore the notion that, compared with its variability, steady-state pupil size is strongly influenced by the concomitant changes in sleep need and circadian phase. In addition, steady-state pupil size appears to be related to motivation and attention, while its variability may be related to separate affective dimensions and subjective fatigue.

Highlights

The pupil is the window through which the brain captures its visual environment, but the pupil is a window to the brain
Saliva samples were collected for subsequent melatonin assays to determine dim-light melatonin onset (DLMO), which was set to circadian phase 0◦ and to which all collected data were realigned
Anxiety was measured by the 21-item Beck Anxiety Inventory (BAI ≤ 14) [33]; mood by the 21-items Beck Depression Inventory II (BDI-II ≤ 14) [34]; sleep quality by the Pittsburgh Sleep Quality Index Questionnaire (PSQI ≤ 7) [35]; daytime propensity to fall asleep in non-stimulating situations by the Epworth Sleepiness Scale (ESS ≤ 11) [36]; chronotype by the Horne-Östberg Questionnaire (58: morning types) [37]

Summary

Introduction

The pupil is the window through which the brain captures its visual environment, but the pupil is a window to the brain. Inhibition of parasympathetic tone by the sympathetic system leads to contraction of the dilator pupillae muscle and to pupil dilation [7]. The latter inhibition has received recent scientific attention because it is directly driven by the locus coeruleus (LC). This brainstem structure is part of the ascending and descending activating systems, and is central to sleep and wakefulness regulation, as well as to cognition and anxiety [8]. PLR and PIPR are widespread means to assess the non-visual or non-image-forming functions of light [12,13,14]

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