Abstract
BACKGROUND: Electrodermal activity (EDA) is a measure of sympathetic arousal that has been linked to depression in laboratory experiments. However, the inability to measure EDA passively over time and in the real world has limited conclusions that can be drawn about EDA as an indicator of mental health status outside of controlled settings. OBJECTIVE: Recent smartwatches have begun to incorporate wrist-worn continuous EDA sensors that enable longitudinal measurement of sympathetic arousal in everyday life. This work (n=237, 4-week observation period) examines the association between passively collected, diurnal variations in EDA and symptoms of depression, anxiety and perceived stress in a large community sample. METHODS: We conducted a prospective, non-randomised study to investigate patterns and relationships between digital device use patterns, including sensor data from phones and wearables reflecting both behavioural and physiological processes, and self-reported measures of mental health and well-being. We recruited 395 participants who had a Fitbit Sense 2 device with the electrodermal sensor activated. We use a non-linear cosinor fitting method to estimate the difference in mesor, amplitude and phase, between the diurnal rhythms in heart rate (HR), heart rate variability (HRV) root mean square of successive differences, EDA, skin temperature and steps. FINDINGS: Subjects who exhibited elevated depressive and anxiety symptoms had higher tonic EDA, skin temperature and heart rate, despite not engaging in greater physical activity, compared with those that were not depressed or anxious. In contrast, subjects who exhibited elevated stress only exhibited higher skin temperature. Most strikingly, differences in EDA between those with high versus low symptoms were most prominent during the early morning. We did not observe amplitude or phase differences in the diurnal patterns. CONCLUSIONS: Results indicate that participants with elevated depressive and anxiety symptoms have different diurnal physiological patterns. Specifically, EDA differences suggest elevated sympathetic activity throughout the day and in particular in the early morning. CLINICAL IMPLICATIONS: Our work suggests that electrodermal sensors may be practical and useful in measuring the physiological correlates of mental health symptoms in free-living contexts and that recent consumer smartwatches might be a tool for doing so.