https://my.clevelandclinic.org/health/body/22279-vagus-nerveEffects of cold stimulation on cardiac-vagal activation in healthy participants: randomized controlled trialhttps://themovementparadigm.com/how-to-map-your-own-nervous-sytem-the-polyvagal-theory/https://counsellinghongkong.com/2021/10/16/polyvagal-theory/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5859128https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3108032/