# Parasympathetic activation

Parasympathetic activation means engaging your 'rest-and-digest' nervous system. It is the calm-down branch of your autonomic nervous system. It works mainly through the vagus nerve. The vagus reaches your chest and upper-abdominal organs. (Pelvic nerves add outflow to your lower gut and pelvic organs.) It slows your heart rate and lowers your blood pressure. It promotes digestion and supports recovery. And it calms inflammation, through the 'cholinergic anti-inflammatory pathway'. You can raise parasympathetic tone with slow, paced breathing, meditation, and deep sleep. That shows up as a higher RMSSD (a heart-rate-variability measure). Cold water on your face also engages the vagus, via the 'dive reflex'. Whole-body cold, by contrast, is mainly a sympathetic stressor, followed by a parasympathetic rebound.

## Sources

- Malik M, Bigger JT, Camm AJ, et al.. (1996). Heart rate variability: Standards of measurement, physiological interpretation, and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. European Heart Journal. https://doi.org/10.1093/oxfordjournals.eurheartj.a014868
- Thayer JF, Lane RD. (2007). The role of vagal function in the risk for cardiovascular disease and mortality. Biological Psychology. https://doi.org/10.1016/j.biopsycho.2005.11.013

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