Answer: He is able to voluntarily activate parts of his central nervous system which allows him to withstand extreme cold temperatures.
Dutchman Wim Hof got the nickname “The Iceman” because of stunts he performed in extreme cold temperatures. He has set multiple Guinness book of world records for longest time immersed in an ice bath - nearly two hours. He also ran a full marathon at the Arctic circle wearing only shorts.
Dr. Otto Muzik and his colleagues at Wayne State performed functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) scans on Hof in early 2018. Through their studies, they discovered that he is able to activate certain parts of his brain through controlled breathing and meditation.
Hof can willingly activate a region of his brain called the periaqueductal gray. This region is a part of the descending pain modulation pathway that acts to inhibit pain signals arriving from the periphery.
Other brain regions he activates during mild hypothermia are higher cortical regions, including left anterior and right middle insula. These are also active during self reflection.
The researchers find that his ability to withstand extreme cold temperatures are a result of unique central nervous system adaptations rather than changes in the periphery.