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  • Writer's pictureJ Felix

Interoception 1: Noting Temperature

Updated: Feb 3

Interoception is the perception of bodily sensations which can express as tingling, throbbing, heat, coldness, pulsing, swelling, tickling, perspiration, contraction, expansion, numbness, pain, etc (Vaitl, 1996; Cameron, 2001; Craig, 2002; Barrett et al., 2004). These perceptions remain largely unconscious. Interoceptive awareness brings these processes to conscious awareness (Cameron, 2001). To experiment, as you read, bring your attention to your feet and note whatever sensations you can: temperature, pressure, etc. This is interoceptive awareness (IA).


The body is performing millions of vital functions now without input from the seeming self or ego. Without thinking, the heart beats, food is digested, cells replicate, proteins are synthesized, toxins are released, bones grow, muscles are repaired, electrolytes are balanced, and you are breathed. Again, as you read, simply notice whether the breath is coming in or out, whether it is fast or slow, deep or shallow. This is interoceptive awareness.


The ability to consciously monitor and feel certain physiological states (such as thirst and hunger), detect potential tissue damage or pain is an adaptation essential for human survival. Again, check in. Are you hungry or full, hot or cold, tired or energetic? This is interoceptive awareness.


Appreciating the complexity that unfolds moment by moment inspires curiosity. Curiosity awakens awe. Awe fosters respect. Respect promotes right thought and right action. Interoceptive awareness deepens self-knowledge. From this centered, informed place, you can respond more thoughtfully when it is time to choose.


This post begins with an exploration of the brain and ends with a meditation to train interoception. Some studies suggest that interoceptive awareness is like vision. That is, some either have good interoceptive awareness (like good vision), and the others have poor IA (like poor vision) (Ehlers, 1990; Ehlers and Breuer, 1996).


Interoceptive awareness can be trained. Meditation promotes anatomical (Lazar et al., 2005; Holzel et al., 2008; Farb et al., 2013; Kang et al., 2013; Fox et al., 2014) and functional brain changes (Farb et al., 2007, 2013; Zeidan et al., 2011; Tang et al., 2012; Fox and Cahn, 2017). As muscles grow when challenged, the brain changes structurally with training. Interoceptive training is linked with increased cortical thickness in the bilateral anterior insula (Farb et al., 2007, 2013, 2015; Paulus et al., 2011; Haase et al., 2016)- which we will explore in more detail below.


The Science

A pea sized structure called the hypothalamus helps the body maintain homeostasis. Homeostasis means balance. When the body is in balance, it maintains stability through change and functions optimally whether at rest or in motion.


The hypothalamus receives information from the internal and external environment: temperature, blood pressure, hormonal levels, gastrointestinal activity (hunger/satiety), etc. The hypothalamus controls our circadian rhythms keeping us alert during the day and controls the secretion of melatonin to help us fall asleep at night. It regulates stress and monitors changes in cortisol (the stress hormone). The hypothalamus gathers and synthesizes this information to correct any imbalances. This is homeostasis.


The hypothalamus regulates your body's temperature like a thermostat. But unlike a thermostat, which simply turns the heat or air conditioning on or off once a desired temperature is reached, the hypothalamus regulates a complex set of temperature-control processes. The hypothalamus balances body fluids, maintains salt concentrations and electrolyte balance, and controls the release of chemicals and hormones related to temperature.


The hypothalamus works with other parts of the body's temperature-regulating system: the skin, sweat glands and blood vessels — the vents, condensers and heat ducts of your body's heating and cooling system. Breathing, sweating, and blood flow are the three primary mechanisms the body uses to regulate temperature.


"I am fearfully and wonderfully made." (Psalm 139:13)

The body has about 200,000 temperature detectors. It's amazing and beautiful to me, how microscopic protein molecules can trigger a behavioral response. "The pursuit of science leads to a religious feeling of a special kind," Einstein observed. A family of ion channels, called thermo-transient receptor potentials or TRPs, are activated by temperature. These thermo-transient receptor potentials (TRPs) provide information about thermal changes in the environment. Six thermo-TRPs have been identified to date: TRP vanilloid (TRPV) 1 and 2 are activated by painful levels of heat, TRPV3 and 4 respond to non-painful warmth, TRP melastatin 8 is activated by non-painful cool temperatures, while TRP ankyrin (TRPA) 1 is activated by painful cold (McNaughton, Vay, Gu, 2012).


When it is warm to hot, say, TRPV3 and TRPV4 will generate signals (action potentials) that are sent to the brain. The hypothalamus reacts by sending messages to the blood vessels, telling them to dilate. This sends warm blood, fluids and salts to the skin, setting off the process of evaporation.


The middle layer of the skin, or dermis, stores most of the body's water. When heat activates sweat glands, these glands bring that water, along with the body's salt, to the surface of the skin as sweat. Once on the surface, the water evaporates. Water evaporating from the skin cools the body, keeping its temperature in a healthy range.


When it is cold, the blood vessels under your skin become narrower (vasoconstriction). This decreases blood flow to your skin, retaining heat near the warm inner body. Your thyroid gland releases hormones to increase your metabolism. This increases the energy your body creates and the amount of heat it produces. Your muscles may produce heat by shivering, keeping body temperature within optimal range.


Your body maintains a constant temperature within one or two degrees of 98.6, yet there is no furnace, no thermostat; there is no HVAC system to keep you cool in summer or warm in winter. While you sleep, the hypothalamus regulates body temperature 24-hours a day every day.


At night, core temperature falls. This explains why we get better sleep in a bedroom set to 67-68º F (19-20º C) than hotter temperatures.


Temperature also affects athletic performance. Regulating body temperature, interestingly, is a lesser known tool for improving performance. ATP is involved in muscular contraction. But the body can't generate more contractions if body temperature gets too hot. Temperature, moreover, dictates recovery as well as how restorative your sleep is.


Cooling the palms of the hands, the bottoms of the feet, and the face passes heat out of body and allows athletes to cool the body and core quickly because the vasculature in the palms, feet, and face is different than other parts of the body. The palms, feet, and face are glabrous. Arteriovenous anastomoses (AVAs) are short vessels in the glabrous skin of the hands, feet, and face that directly connect small arteries and small veins, bypass capillaries, and quickly shunt blood (Walloe, 2015). AVAs allow more heat to leave and more cool to enter the body more quickly than any other part. So, one way to optimize athletic performance is to expose the hands, feet, or face to cold for 30 seconds to a minute. Professor Craig Heller at Stanford University found that by taking advantage of specialized heat-transfer veins in the palms of hands, researchers could rapidly cool athlete's core temperatures, dramatically improving exercise recovery and performance. Athletic performance was “equal to or substantially better than steroids… and it’s not illegal.”


I hold cold things or run my hands in cold water for about a minute and a half during rest periods to boost performance.


Cold boosts mitochondrial biogenesis, increasing their number (Chung, 2017; Jornayvaz, 2010). Cold water immersion stimulates the production of PGC-1 alpha in skeletal muscles. PGC-1⍺ is a protein that regulates mitochondrial biogenesis. Increased mitochondrial biogenesis is an adaptation associated with greater aerobic capacity.


I take a 3-5 minute ice bath several times per week before training to improve mitochondrial health, aid muscle recovery, and improve my mood. Cold plunges before exercise may increase testosterone levels as well as luteinizing hormone levels (Katsuno, 1991). One middle aged doctor reported his testosterone levels jumped from 728 ng/mL (which is very good) to 1180 ng/mL, which is almost unheard of in a 52 year old.


Heat can also be beneficial. Exercising after heat can be much more challenging as body temperature regulates exercise performance. Exposure to heat and cold accelerates recovery and challenges the vascular system. Going from heat to cold to heat to cold requires the body to adapt as vessels dilate and constrict, dilate and constrict.


Heat training mimics many of the physiological benefits associated with exercise- increased body temperature and heart rate, sweating, etc. A 2015 study found an association between sauna bathing and reductions in sudden cardiac death, fatal coronary heart disease, fatal cardiovascular disease, and all-cause mortality. In a 2017 study, researchers found that moderate to high frequency of sauna bathing was associated with lowered risks of dementia and Alzheimer's disease. While the mechanisms are not completely understood, a type of stress response protein called heat shock protein appears to play a role. Heat shock proteins help other proteins maintain their structure and integrity. Cells degrade as we age. So anything that prevents cellular instability is welcome. When proteins no longer replicate faithfully, they form aggregates which form plaques in the vascular system (e.g. atherosclerosis) or in the brain (e.g. amyloid beta plaques). Elevated levels of heat shock proteins may delay or prevent this unraveling.


As they burn up energy, every cell in the body produces heat. Blood circulates heat.

Your temperature doesn’t stay the same all day, and it will vary throughout your lifetime. Some things that cause your temperature to vary during the day include:

  • Time of day

  • Age

  • Gender

  • Activity level

  • Health

  • What you’ve eaten or had to drink

  • Where you are in your menstrual cycle

  • Emotional state

Our emotional state can induce changes in body temperature. Anger, for example, leads to vasoconstriction. The blood vessels narrow. This may cause the body to heat up quickly. Interestingly, clusters of neurons within the hypothalamus control aggression, rage, mating behavior, and motivation.


Some people sweat when they are anxious, to give another example. This is the body's response to vasoconstriction - your body knows it's about to heat up, so it sweats to help you cool down. Anxiousness may also cause excessive movement, wringing of the hands, agitated pacing back and forth, etc. This may heat up your body further.


If I am experiencing fear, I may get goosebumps, which may cool the body. Hyperventilation- or rapid, shallow breathing- can also lead to body cooling.


Acute stress triggers peripheral vasoconstriction- your body will begin to shift blood flow from your extremities (hands, feet, arms, and legs) and outer skin to the core (chest and abdomen)- causing a rapid, short-term drop in skin temperature (Herborn et al., 2016). This influx of peripheral blood, along with stress-induced thermogenesis (heating), simultaneously increases core temperature.


"Our emotional system in the brain sends signals to the body so we can deal with our situation," says Lauri Nummenmaa, a psychologist at Aalto University who led a study that mapped bodily sensations connected to certain emotions (Nummenmaa, 2018).




"Say you see a snake and you feel fear," Nummenmaa says. "Your nervous system increases oxygen to your muscles and raises your heart rate so you can deal with the threat. It's an automated system. We don't have to think about it."


Where the hypothalamus regulates temperature, another part of the brain, the insula, interprets and gives meaning to these changes in bodily sensations. The insula is the primary hub for interoception. The insula and surrounding neural circuits are believed to be responsible for other functions beyond interoception including attention, awareness, and interpreting subjective experiences.


Meditation: Interoceptive Training & Research

Different meditation techniques have different attentional profiles. Non-reactivity may be the attentional style in one technique, de-centering may be the focus of another. Skilled meditators can investigate complex interoceptive signals in different ways. How we train modulates the insula in different ways (Gibson, 2019). Interoceptive awareness changes intra-insula signal flows- that is, how the signals move within the insula- e.g. posterior (back) to anterior (front) (Kuehn, 2015). More experienced meditators, for example, can count their heartbeats with greater accuracy than controls (Chong, 2016). The ability to detect heartbeat is a measure of interoceptive accuracy. By slowing brain activity, signals along the posterior-to-anterior insula pathway allow the salient and noiseless detection of one's own heartbeat (Kuehn, 2015). Heartbeat sensors are also spread out all over the brain (Salameh at al., 2024). The pulse can be sensed directly in the brain and brought to conscious awareness. How your heart is beating could affect how you think and feel. We can tune into that.


This is extremely useful data. As an athlete, for example, I might train to max out my heart rate and improve my VO2 Max- which we can liken to the horsepower in an engine. Post-exercise the faster I can lower my temperature and return my heart rate to baseline, the faster my recovery.


Meditators learn experientially that there are sensations and there are the stories we tell ourselves about these sensations. People often confabulate them and experience these unfoldings as a "feeling." A signal from somewhere in the body travels to the brain. The raw data is one thing. Perception is another. Our appraisals, attitudes, beliefs, past experiences, expectations, controllability, and context color our perceptions (Cameron, 2001; Craig, 2009; Mehling et al., 2012; Farb et al., 2015) and our perceptions provide a moment-by-moment commentary on the body’s internal state (Craig, 2009; Khalsa et al., 2018).


Interoception is the interplay between perceptual body states and cognitive appraisal of those body states (Farb et al., 2015). Our inner lives are organized around the stories we tell ourselves as sensations arise and influence our physical and psychological well-being.


Interestingly, major depressive disorder and the somatic symptoms and bodily aches that often accompany depression are associated with abnormal interoceptive representation within the insula (Avery, 2014).


Heightened awareness of bodily sensations can serve as a marker for a variety of mental disorders including anxiety, panic disorder, depression, eating disorders, and somatization (Cioffi, 1991; Pollatos et al., 2008, 2009; Mehling et al., 2009; Herbert and Pollatos, 2014; Mallorquí-Bagué et al., 2014; Fischer et al., 2017). Maladaptive forms of interoceptive awareness are characterized by hypervigilance and catastrophizing (Hanley et al., 2017). Those diagnosed with any of the above conditions may find increased awareness to bodily sensations distressing (Baas et al., 2004; Mehling et al., 2009) and should exercise care and judgment when practicing body scan techniques.


That said, much of the research on interoceptive awareness has found a positive relationship between the degree of awareness and emotional regulation (Wiens, 2005; Dunn et al., 2007; Herbert et al., 2011), decision making (Dunn et al., 2012; Sütterlin et al., 2013), empathy (Singer et al., 2009; Fukushima et al., 2011), and behavioral regulation (Herbert et al., 2007, 2012; Herbert and Pollatos, 2014).


Tony Robbins, a life coach, tells a story that illustrates the difference between sensation and perception. Tony coached two professional singers- Carly Simon and Bruce Springsteen. Both felt the same kinds of physical sensations before they went on stage. "When I’m about to go on stage, my heart starts racing, my palms start sweating and I get butterflies in my stomach. I start to get this tingling sensation throughout my body through to my fingertips…and that’s when I know I’m having a panic attack." For Carly, these sensations triggered alarm, but for Bruce, they made him feel more alive. "When about to go live, my heart starts racing, my palms start sweating and I get butterflies in my stomach. I start to get this tingling sensation throughout my body through to my fingertips…and that’s when I know I’m excited and ready to rock the audience."


Practice

The body is performing countless tasks now. Moment by moment new sensations will arise and pass away. The brain is processing most of these signals below conscious awareness. For this exercise, we will focus primarily on temperature. With eyes closed, create a map of the body. Then visit every part, like a meteorologist, and simply observe the temperature of each part.




Like a scientist, you're merely reporting what you experience without evaluating as "good" or "bad," "desirable" or "undesirable," "welcomed" or "unwelcomed." You are simply observing. If you feel heat in a certain region, for example, go deeper. How far does it extend? How deep does it go? What is its quality? Start from the top of the head and scan down to the tips of the toes. Approach this exercise with openness and curiosity, expecting nothing. Just notice, analyze nothing.





First published 7/8/2022

Edited and republished 9/11/2023




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