Project Summary/Abstract Stress, both physical and psychological, is associated with compromised autonomic function, altering either parasympathetic or sympathetic nervous system activity. Autonomic dysfunction is implicated in physical (obesity/diabetes, etc.), psychological (anxiety/mood disorders, etc.) and neurological (Parkinson's, etc. ) disorders, making it critical to develop reliable measures of system function. A classic cardiovascular measure of parasympathetic function computes the variability in the beat-to-beat electrocardiogram, but, recently, existing cardiovascular measures of sympathetic nervous system activity have been called into question, prompting a search for new technologies. This exploratory proposal investigates pupillometry as a novel measure of autonomic function, since pupil diameter is under the control of two muscles - the sphincter and dilator - that are separately innervated by parasympathetic or sympathetic nervous system activity, respectively. Recent data from our laboratory suggest that different independent variables – the brightness and emotional arousal of visually presented stimuli – can be used to independently index activity mediated by the parasympathetic (sphincter) or sympathetic (dilator) nervous system. This proposal is the first to suggest that pupil diameter may serve as a new, non-invasive, easy-to-measure index of autonomic function and it's specific aims include: 1) assessing the test-retest reliability, agreeability, and validity of autonomic estimates based on pupil diameter in separate bi-weekly assessments. 2) compare autonomic estimates based on pupillary measures to classical cardiovascular estimates of autonomic function, and 3) explore whether estimates of autonomic function defined by pupil diameter covary as expected based on demonstrated individual differences in autonomic profiles based on body mass index, core negative affect, and aerobic exercise. To the extent that pupil diameter serves as a reliable, valid index of autonomic system function that is sensitive to individual differences, it promises an exciting new avenue in diagnosing autonomic dysfunction in a variety of physical, psychological, and neurological disorders, as well as in assessing effects of treatment on autonomic nervous system action.