Detecting sleepiness in seasonal depression using the pupillary unrest index (PUI): Associations with actigraphic sleep behavior

Daytime sleepiness and fatigue are common, yet hard to distinguish in depression. Sleepiness often reflects homeostatic sleep need caused by insufficient/disrupted sleep, and detection is critical for tailoring sleep-focused treatment in depression. However, misattributing fatigue to sleepiness is common on self-report, and terms like sleepy and tired are used interchangeably. The Pupillary Unrest Index (PUI) from the Pupil Sleepiness test (PST) is an objective measure of alertness that may help detect sleepiness due to insufficient/disrupted sleep. Currently, data linking the PUI to recent sleep behavior are limited and no study has examined these associations in depression. In a sample with varying levels of seasonal depression disorder (SAD) symptoms, we hypothesized that actigraphic sleep behaviors (duration, wake after sleep onset, sleep latency, efficiency, awakenings) would be associated with the PUI, and these associations would be stronger than those with self-reported sleepiness. We recruited 46 participants ranging from no history of depression through severe SAD. Assessments included the PUI, actigraphy 1-3 nights before the PUI, and self-reported sleepiness and fatigue. The PUI was not associated with SAD severity, fatigue, or self-reported sleepiness, whereas higher self-reported sleepiness was associated with higher SAD severity and fatigue. Longer sleep duration across 1-3 cumulative nights of sleep was associated with lower PUI. Shorter prior-night sleep latency was associated with higher next-day PUI. Both sleep duration and sleep latency were stronger predictors of the PUI than self-reported sleepiness. Results suggest the PUI can detect sleepiness associated with recent prior sleep behaviors, and diverges from SAD symptomology.