He's called the "Iceman" for good reason.

Dutch adventurer Wim Hof is a human icicle — a man with incredible tolerance for cold. He holds the Guinness World Record for sitting in an ice bath for one hour, 52 minutes and 42 seconds — something most people can only tolerate for a few seconds.

Hof attributes this remarkable endurance and ability to a special meditation and breathing technique he's developed, which he says promises to "light your inner fire."

Scientists from Wayne State University are now using sophisticated brain imaging technology to try to understand how Hof does it.

It's all about breathing

The secret to Hof's technique is a regimen that is meant to prepare the body for its encounter with extreme cold.

The first step is forced exhalations, which drops the level of carbon dioxide in the blood.

This creates a situation similar to hyperventilation, and usually triggers a range of symptoms including dizziness and light-headedness.

Practitioners of the Wim Hof method are trained to recognize this, and respond by holding their breath for up to 90 seconds.

This, in turn, causes a plunge in the oxygen saturation of the blood, another major stressor for the body that creates a sensation similar to suffocation.

However, those trained in Hof's meditation and breathing method can cope with this stress and are ready, if they want, to plunge into the cold.

Wim Hof and Dr. Otto Muzik prepare for a run in an fMRI brain scanning device (Wayne State University)

Throwing cold water on the mystery

Dr. Otto Muzik, an associate professor in the Faculty of Medicine at Wayne State University, used fMRI and PET scanning devices to peer into Hof's brain as he entered his breathing regimen wearing a special suit that circulates cold water around his body, to observe his cold tolerance.

Dr. Muzik discovered two ways in which Hof seemed to be able to manipulate his physiology to tolerate the cold.

Hof was able to increase activation in thermoregulatory areas of the brain and drive heat generation to protect his skin and extremities from cold damage.

He's also able to increase the release of chemicals in the brain called endocannabinoids, which create a sensation of euphoria, to help numb the pain of the cold.