Relating pupil diameter and blinking to cortical activity and hemodynamics across arousal states

Arousal state affects neural activity and vascular dynamics in the cortex, with sleep associated with large changes in the local field potential (LFP) and increases in cortical blood flow. We investigated the relationship between pupil diameter and blink rate with neural activity and blood volume in the somatosensory cortex in male and female unanesthetized, head-fixed mice. We monitored these variables while the mice were awake, during periods of rapid eye movement (REM), and during non-rapid eye movement (NREM) sleep. Pupil diameter was smaller during sleep than in the awake state. Changes in pupil diameter were coherent with both gamma-band power and blood volume in the somatosensory cortex, but the strength and sign of this relationship varied with arousal state. We observed a strong negative correlation between pupil diameter and both gamma-band power and blood volume during periods of awake rest and NREM sleep, though the correlations between pupil diameter and these signals became positive during periods of alertness, active whisking, and REM. Blinking was associated with increases in arousal and decreases in blood volume when the mouse was asleep. Bilateral coherence in gamma-band power and in blood volume dropped following awake blinking, indicating a 'reset' of neural and vascular activity. Using only eye metrics (pupil diameter and eye motion), we could determine the mouse’s arousal state (‘Awake’, ‘NREM’, ‘REM’) with greater than 90% accuracy with a 5-second resolution. There is a strong relationship between pupil diameter and hemodynamics signals in mice, reflecting the pronounced effects of arousal on cerebrovascular dynamics.

Methods
See the methods section of the manuscript.