This latest episode of Science on the Rocks offers a sneak preview of Wayne State University's unpublished study on thermoregulation, which yielded surprising results and promising new insight into the physiological mechanisms stimulated by cold exposure.
Professors Otto Muzik and Vaibhav Diwadkar, two neuroscientists working at Wayne State University’s School of Medicine in Detroit, Michigan, set out to investigate the correlates of thermoregulation in the human brain and body.
Since you cannot do functional magnetic resonance imaging when people are sitting in a bathtub, these guys use something called a “cold suit”, which is a kind of jumpsuit with small plastic tubes woven into it. These tubes are used to perfuse either skin-tempered or cold water to induce mild hypothermia while people undergo functional imaging.
What they found is that there is a hierarchically organized thermoregulatory network that distinguishes between cold and warm stimuli. When skin temperatures dropped, so did the brain activation in the midbrain, the anterior insula, the anterior cingulate and the inferior parietal lobule. The opposite trend —greater brain activation with cooling— was observed in the bilateral orbitofrontal cortex (OFC), an area right behind your eyes. As usual the brain cares more about changes than it cares about stability. The brain activation they observed was primarily related to the cooling and warming phases that cause comparably large changes in core body temperature per unit of time. From that, Otto and Vaibhav conclude that the thermoregulatory network generates a very precise internal representation of the body’s condition. This is relayed to the OFC, which then promotes a higher-order integration of internal states and emotional significance, which in turn may or may not motivate behavior. In the case of cold, that might include changing your environment by seeking shelter from the cold, putting on a sweater, or simply moving your large body muscles to generate heat, also known as shivering.
But then, their PhD students told them about this crazy Dutch guy who had almost superhuman capacities when it comes to withstanding cold exposure, and it quickly became clear that they had to invite Wim Hof, along with a group of controls, to their lab for some tests. They underwent fMRI and PET/CT scans while exposed to mild hypothermia. Wim did this with and without practicing his method beforehand.
Before they did the imaging session, Wim and the control group put on the “cold suit”. Then, temperature-controlled neutral water of 31-34°C or cold water of 15-17°C was circulated through the tubes. They monitored skin temperature, subjective feelings of cold, neural activity in the fMRI scanner and abdominal/thoracic brown fat activation in the PET/CT scanner.
Measurements of Wim were acquired on three different days; the control group came in on two days.
On Day 1, the pre-scan “passive” measurement took place. What this means is that all participants including Wim underwent an oscillating whole body temperature challenge that creates periods of mild hypothermia (not really cold for Hoffers), mixed with periods of return to basal core body temperature.
On Day 3, all participants including Wim underwent a whole-body PET/CT scan during moderately cold conditions in a “passive” state. So essentially what they did on Day 1, but inside the PET/CT rather than the fMRI scanner.
Wim was explicitly asked to refrain from all breathing and focusing exercises, prior to the PET/CT scan. The scan protocol that Otto and Vaibhav employed allowed them to monitor sympathetic stimulation and glucose consumption of brown adipose tissue (or brown fat) under cold exposure, as well as changes in daily energy expenditure, compared to the neutral temperature conditions.
Now, given that Wim uses a very controlled way of breathing, and given that the WHM also involves mental focus as a major ingredient, one would assume that cold exposure after practicing the WHM would entail greater brain signal responses in brain regions that are associated with volitional control, such as the dorsolateral prefrontal cortex.
Much to the researcher’s surprise however, they found that the WHM activates the Periaqueductal gray (PAG), a lower-level brain region that controls descending pain/cold stimuli modulation, possibly initiating a stress-induced analgesic (pain-reducing) response. While the research team did find activation in higher-order cortical areas (more specifically the left anterior and right middle insula), these are areas that are primarily associated with self-reflection: promoting internal focus and sustained attention— also in the presence of averse external stimuli, like cold.
The other striking finding from this study was that a dedicated practice of forceful breathing did lead to increased sympathetic innervation and glucose consumption, but not where the researchers expected it to: instead of more activation in brown adipose tissue, they found this to be true for the intercostal muscles (the muscles between your ribs that are majorly involved in breathing). This led them to hypothesize that instead of brown fat passively keeping you warm, the intercostal muscles might be generating heat that spreads over to the tissue of the lungs and warms the circulating blood in the pulmonary capillaries. From there, the warm blood is circulated through the body, reaching the periphery, which might also explain why Wim does not suffer from frost bite in his extremities when he spends long times in icy conditions.
So in a nutshell, the strong involvement of the periaqueductal gray suggests a systemic release of endogenous opiates and cannabinoids that could lead to the decreased sensitivity to cold, and the feeling of euphoria and well-being that is often described in the wake of cold exposure.
It also seems that these results support the primacy of the brain over the body when it comes to Wim’s remarkable responses to cold.
This amazing, yet to be published study provides another piece of the scientific puzzle for what Wim has claimed for a long time: that his method allows you to hack into key components of the autonomic nervous system, with all the larger implications for lifestyle interventions and, even more so, for ameliorating symptoms of various types of illness!
Check out the podcast to hear co-host Dina interview the researchers, Otto and Vaibhav, about the set-up & surprising results of the study.
Matthias Wittfoth is a neuroscientist & co-host of Science on the Rocks.