Modern Pupillometry : Springer : 9783031548956 : 3031548957 : 01 Jul 2024 : Pupillometry, the study of the eyes' pupils, has a rich history, dating back to the 1800s.  For example, to appear "dark with desire," women once used atropa belladonna (deadly nightshade) as a cosmetic, because the atropine dilated their pupils, making them appear more romantically aroused. We now know that this relationship is largely driven by the activity of the sympathetic nervous system; specifically, a small brainstem nucleus known as the locus coeruleus (LC). Because of tight connections between the musculature of the eyes and LC, monitoring the pupils can reveal important insights into brain activity during mental processes. Many of these processes are related to attention and arousal (cognitive or emotional), with the LC controlling mental readiness via secretion of the neurotransmitter norepinephrine. While these complicated neurochemical processes happen in the brain, they are often overtly observab