Parasympathetic activation

Parasympathetic activation refers to engagement of the rest-and-digest branch of the autonomic nervous system, primarily mediated by the vagus nerve to thoracic and upper-abdominal organs, with additional outflow via pelvic splanchnic nerves to lower GI and urogenital organs. It slows heart rate, lowers blood pressure, promotes digestion, and supports recovery while modulating inflammatory tone via the cholinergic anti-inflammatory pathway. Slow paced breathing, meditation, and deep sleep raise parasympathetic tone, reflected in higher RMSSD. Cold-water face immersion engages the vagus via the dive reflex, while whole-body cold is primarily a sympathetic stressor with a parasympathetic rebound.