Pupils protecting sleep

Curr. Biol. 28, 392–400.e3 (2018)

Pupil dilation can reflect arousal, vigilance level, emotions, and even choice preferences. But what about sleep? Lead author Daniel Huber of the University of Geneva and his colleagues wondered if pupil size reflects the state of the cortex, and whether changes in the pupil might affect sleep.

They combined electrophysiology measurements with pupil measurements in naturally sleeping mice, and found that pupil size could reliably predict whether the animal was in the rapid-eye movement (REM) stage, the non-REM stage, or awake. Constriction of the pupil might shield sleeping animals from visual stimuli that could awaken them. This idea was reinforced when researchers artificially dilated one pupil and found that light flashes directed towards it led to sleep state changes, but no changes occurred when flashes were directed to the pupil in the sleep state.