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

Figures

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  Figure 1. Experimental protocol. After an 8-h baseline night of sleep under polysomnographic recording, participants (N = 20) underwent 29 h of sustained wakefulness in constant routine conditions in dim-light (<5 lux at eye level). Pupil size was assessed 12 times immediately after a test battery including the psychomotor vigilance task (PVT). Spontaneous waking electroencephalographic (EEG) recordings were acquired 8 times. Saliva samples and subjective scores for sleepiness, fatigue and affective state were collected hourly. Time is expressed in expected circadian phase (degrees °; 15° = 1 h) and equivalent elapsed time awake (h). Relative clock time displayed here is for a participant with a 24:00–08:00 sleep-wake schedule. Arrow indicates expected time of dim-light melatonin onset (circadian phase 0°).

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  Figure 2. Time course of pupil measures during 29 h of sustained wakefulness (mean ± sem). (A) Steady-state pupil size (mm2) significantly varied with circadian phase. (B) Pupil size variability (mm2 s−1) did not yield significant variation with circadian phase. Refer to main text for outputs of statistical tests. Average melatonin profile is displayed in grey. Time course is expressed relative to individual dim light melatonin onset (DLMO = phase 0°; 15° = 1 h).

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  Figure 3. Time course of subjective sleepiness and fatigue, objective alertness and attention (mean ± sem). (A) Subjective sleepiness (Likert scale). (B) Subjective fatigue (visual analogue scale, arbitrary units—a.u.). (C) Mean reaction times during PVT. (D) Relative EEG theta power (4.5–7.5 Hz). All four variables significantly varied with circadian phase. Refer to main text for outputs of statistical tests. Average melatonin profile is displayed in grey. Time course is expressed relative to individual dim light melatonin onset (DLMO = phase 0°; 15° = 1 h).

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  Figure 4. Linear associations between steady-state pupil size and PVT performance and between pupil size variability and subjective fatigue. (A) Regression between steady-state pupil size and mean reaction time during a PVT across all circadian phases. (B) Regression between pupil variability and subjective fatigue (assessed with a VAS) irrespective of circadian phase. (C) Regressions, considering each circadian phase separately, indicating that increase subjective fatigue is associated with decrease pupil size variability. (D) Regressions, considering each circadian phase separately, indicating that increase subjective fatigue is associated with increase pupil size variability. Phases included in panels B and C are indicated in the insets. Refer to main text for outputs of statistical tests. Regressions were used for visual display only, and not as a substitute of the full GLMM statistics presented in Table 2. GLMMs were set according to dependent variables distribution.

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  Figure 5. Time course of subjective affective dimensions (mean ± sem; arbitrary units—a.u.). All five variables significantly varied with circadian phase. Refer to main text for outputs of statistical tests. Average melatonin profile is displayed in grey. Time course is expressed relative to individual melatonin onset (DLMO = phase 0°; 15° = 1 h).

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  Figure 6. Significant linear associations between pupil measures and subjective affective dimensions (arbitrary units—a.u.). (A) Significant linear associations between steady-state pupil size and motivation. (B) Significant linear associations between pupil size variability and sociability. (C) Significant linear associations between pupil size variability and anguish. Refer to main text for outputs of statistical tests. Regressions were used for visual display only, and not as a substitute of the full GLMM statistics presented in Table 3. GLMMs were set according to dependent variables distribution.