Arousal state dependence of the cortical blood volume - pupil diameter relationship

Arousal state profoundly affects neural activity and vascular dynamics in the cortex, with sleep causing large changes in local field potentials (LFP) and increases in blood flow. Here we investigate how arousal state dictates the relationship between external measures of arousal, pupil diameter and blink rate, with neural activity and blood volume in the somatosensory cortex in both male and female head-fixed mice and determine whether optical measures of pupil diameter can accurately predict arousal state for classifying of neural data. Pupil diameter was consistently smaller during REM and NREM sleep than in the awake state. Pupil diameter changes were coherent with both changes in blood volume and gamma-band power in the somatosensory cortex, but the strength and sign of this relationship varied with behavioral state. We observed a strong negative correlation between pupil diameter and both blood volume and gamma-band power during periods of rest and sleep, though the correlations between pupil diameter and blood volume became positive during periods of alertness and active whisking, consistent with fidgeting and other body motions driving vasodilation in the somatosensory cortex. Blinking was associated with increases in arousal, and subsequent large decreases in blood volume when the mouse was asleep. Coherence of bilateral measures of gamma-band power and blood volume dropped immediately following a blink, indicating a 'reset' of vascular and neural activity. Using only pupil diameter, we could determine if the mouse is awake or asleep with high accuracy with a temporal resolution of seconds. Our results demonstrate a very strong reciprocal relationship between pupil diameter and hemodynamics signals in unanesthetized mice, reflecting the pronounced effects of arousal on cerebrovascular dynamics. ### Competing Interest Statement The authors have declared no competing interest.