Sleep in Extreme Environments: Part Two.

Sleeping in Extreme Environments

U.S. Marines of the 15th Expeditionary Unit (MEU) Fox Company "Raiders" sleep-wearing respirators during a gas attack alert in an undisclosed location in the Iraqi desert on March 28, 2003 (Ingersoll, n.d.) (Reuters).

How NASA astronauts sleep aboard the International Space Station that orbits the Earth (Callini, 2015).

Deep within the Leuser Ecosystem on the island of Sumatra, Indonesia (Melanie Boling, Imagery Beyond Borders, 2017).

Sleeping and Thermoregulation in Extreme Environments

The behavior of humans accounts for about 90% of their thermoregulation. “Under ambient conditions, the core body temperature of 37 degrees celsius is maintained by the permanent metabolic active internal organs such as the brain, heart, liver, and gastrointestinal tract through a fine-tuned thermoregulatory system that mainly adjusts peripheral perfusions of the skin and evaporation by the sweat glands to the thermal needs of the body.” (Gunga, 2015).

Human’s core body temperature begins to decrease a few hours before sleep onset. The thermal environment is one of the most important factors that can affect human sleep. Effects of heat or cold exposure are increased wakefulness and decreased rapid eye movement (REM) sleep and slow wave (SWS) sleep. Heat exposure increases wakefulness and decreases SWS and REM sleep. Humid heat exposure further increases thermal load during sleep and affects sleep stages and thermoregulation (Okamoto-Mizuno & Mizuno, 2012). “Heat loss in hot and warm environments and under strenuous exercise, the organism depends on the evaporative pathway” (Gunga, 2015).

“Cold exposure affects cardiac autonomic response during sleep without affecting sleep stages and subjective sensations. The impact of cold exposure may be greater than that of heat exposure” (Okamoto-Mizuno & Mizuno, 2012). “In cold environments, heat loss must be reduced in order to prevent hypothermia. Thus, the body shell has to be enlarged via vasoconstriction, which allows better insulation of the core (which protects vital organs). Insulating layers prevent heat loss” (Gunga, 2015).

During non-rapid eye movement (NREM) sleep, the brain, and core temperature decrease with magnitudes irrespective of the ambient temperature (Okamoto-Mizuno & Mizuno, 2012). NREM sleep is a state with a low level of energy metabolism, cardiovascular, and thermoregulatory functions to conserve energy while feeding is reduced. Central autonomic nervous system activity regulating cardiovascular function and breathing as well as endocrine function supports this need during NREM sleep. Energy conservation and cooling of the body and brain are thought to be major functions of the tight interconnection of sleep and thermoregulation.

“Thermoregulation is a mechanism by which mammals maintain body temperature with tightly controlled self-regulation independent of external temperatures. Internal temperature regulation is a type of homeostasis and a means of preserving a stable internal temperature in order to survive” (Osilla et al., 2022). The human core body temperature consists of cranial, thoracic, and abdominal cavities. Together, their median core body temperature is about 37 degrees Celsius. The temperature of human extremities is considerably lower and ranges from about 28-36 degrees celsius (Gunga, 2015). Core body temperature is not consistent, and fluctuates throughout the day via circadian rhythm.

Our internal body temperature is regulated by the hypothalamus. The hypothalamus checks our current temperature and compares it with the normal temperature of about 37°C. “If our temperature is too low, the hypothalamus makes sure that the body generates and maintains heat. If our current body temperature is too high, heat is given off or sweat is produced to cool the skin.” (Gunga, 2015). Humans require a constant high core body temperature between 36.4- 37.4 degrees celsius.

Humans are endothermic organisms, (less dependent on external environmental temperatures) (Gunga, 2015). “Endothermic Organisms have much higher basal energy consumption - this keeps the core body temperature constant throughout a wide range of different external environmental temperatures.” (Gunga, 2015). Variations of core body temperature are only tolerated in a very small range.

(*Thermoregulation in Humans - Body Temperature Regulation at Night*, n.d.)

The Brain and Sleep in Extreme Environments

The Preoptic Area of the Hypothalamus (POAH) serves as a critical brain region that influences thermoregulation, sleep, and energy homeostasis. The POAH is also involved in regulating parenting, and sexual behaviors, each of which is controlled by dedicated circuits (Frontiers | Role of the Preoptic Area in Sleep and Thermoregulation, 2021).

The control circuit consists of the motor system, brown adipose tissue, vasomotor activity, sweat secretion, and pilomotor activity. “A critical role of the POAH in integrating temperature information and triggering behavioral and autonomic responses through their central and peripheral downstream targets to adjust the body temperature” (Frontiers | Role of the Preoptic Area in Sleep and Thermoregulation, 2021). The POAH is where body shell and body core temperatures are compared to set-point values.

A Set-Point Value is set by means of temperature reference signals placed within the brain and body’s control circuit (Gunga, 2015). A decrease of the core body temperature below the setpoint value set by the hypothalamus leads to vasoconstriction of the skin and shell vessels (negative feedback), whereby the heat release via the body shell is reduced, piloerection of the hair (goosebumps), enlarges the insulating boundary layer above the skin and thus decreases the heat loss; and increased heat production by shivering. When the actual value, on the other hand, lies above the setpoint value, all those mechanisms that might evoke a further increase in the body temperature (motor system) are extenuated (negative feedback), and the mechanisms of heat loss are strengthened (vasodilatation in the body shell, increase of sweat secretion).

In the Hypothalamus, special neurons produce signals independent of the temperature. “When temperature and set-point value deviate from each other, various elements within the control circuit are changed by the autonomic nervous system to affect vegetative nerve fibers within the control circuit of positive and/or negative feedback” (Gunga, 2015). Different defense mechanisms for the maintenance of the core body temperature are reflexes and cannot be influenced entirely through autonomic control (Gunga, 2015).

Sensations of thermal comfort or discomfort are generated within the sensory cortex. Stimulating the internal and external cold and heat receptors via the tractus spinothalamicus and the unspecific medial thalamic regions (Gunga, 2015). “With distinct thermal discomfort, not only a stimulation of the autonomic countermeasures is initiated, but also, mediated via the cortex, changes in behavior, which leads to the selection of warmer clothing or taking shelter in a heated room in a cold environment” (Gunga, 2015).

*(Hypothalamic-Pituitary-Adrenal (HPA) Axis | Simply Psychology*, n.d.)

“The hypothalamic–pituitary–adrenal (HPA) axis is the major neuroendocrine axis that regulates homeostasis in mammals” (Gjerstad et al., 2018). “Glucocorticoid hormones (GH) are synthesized and secreted from the adrenal gland in response to stress. GH has a wide range of effects as they are involved in the regulation of metabolic processes, immune system, reproduction, behavior and cognitive functions” (Gjerstad et al., 2018). “Under basal conditions, glucocorticoids are released rhythmically with both a circadian and an ultradian pattern. These rhythms are important not only for the normal function of glucocorticoid target organs but also for the HPA axis responses to stress” (Gjerstad et al., 2018). When stress activates the HPA axis the resultant increase in cortisol in order to prepare the body to cope with and recover from the stressor. This is also known as resilience (Gjerstad et al., 2018).

A principal mediator of the impact of stress on the brain and behavior is the activation of the hypothalamic-pituitary-adrenal axis, which results in widespread hormonal, neurochemical, and physiological alterations (Russo et al., 2012). Inflammatory stimuli in the brain and behavior have consistently reported evidence that inflammatory cytokines affect the basal ganglia and dopamine neurotransmission (Felger, 2017). Examination of the mechanisms by which cytokines alter the basal ganglia and dopamine function will provide insights into the mitigation of cytokine-induced behavioral changes and malaise due to an inflammatory response from HPA axis dysfunction.” (Felger, 2017). Findings have included inflammation-associated reductions in ventral striatal responses to reward, decreased dopamine and dopamine metabolites in cerebrospinal fluid, and decreased availability of striatal dopamine (Felger & Miller, 2012).

Dopamine response exhibits increased peripheral cytokines and other inflammatory markers, such as c-reactive proteins or autoimmune and/or fibromyalgia response to stressors such as exposure to extreme environments (Felger & Miller, 2012). Dysfunction of neurotransmitters and their receptors can lead to dopamine-relevant corticostriatal reward circuitry. Inflammatory stimuli on the brain and behavior have consistently reported evidence that inflammatory cytokines affect the basal ganglia and dopamine (Boling, 2021).

Neuroadaptations in the brain and their neuroendocrine output contribute to resilience. The ability to avoid behavioral changes in response to chronic stress is mediated not only by the absence of key molecular abnormalities that occur in susceptible animals/humans to impair their coping ability but also by the presence of distinct molecular adaptations that occur specifically in resilient individuals to help promote normal behavioral function (Russo et al., 2012).

Sleep plays a vital role in this regulation.

A U.S. soldier of 2-12 Infantry 4BCT-4ID Task Force Mountain Warrior takes a break during a night mission near Honaker Miracle camp at the Pesh valley of Kunar Province August 12, 2009 (Ingersoll, n.d.) (Reuters).

Sleep in Extreme Environments: Part Three, Countermeasures and Mitigation Techniques, Coming Soon.

References

Boling, Melanie. (2022). Melanie Noelani Boling. Imagery Beyond Borders. https://imagerybeyondborders.org

Boling, Melanie (2021). Reported results of Amazonian Entheogens for treatment of Complex-Post-Traumatic Stress Disorder (C-PTSD); Military Sexual Trauma (MST); and Traumatic Brain Injury (TBI) among U.S. Military Veterans and the benefits of application through small group indigenous shamanic ceremonies. The Amazon Rainforest: From Conservation to Climate Change-research. Harvard Summer School, August 9, 2021

Callini, C. (2015, February 24). Sleeping in Space [Text]. NASA. http://www.nasa.gov/image-feature/sleeping-in-space

Felger, J. C., & Miller, A. H. (2012). Cytokine effects on the basal ganglia and dopamine function: The subcortical source of inflammatory malaise. Frontiers in Neuroendocrinology, 33(3), 315—327. https://doi.org/10.1016/j.yfrne.2012.09.003

Felger, J. C. (2017). The Role of Dopamine in Inflammation-Associated Depression: Mechanisms and Therapeutic Implications. Current Topics in Behavioral Neurosciences, 31, 199–219. https://doi.org/10.1007/7854_2016_13

Frontiers | Role of the Preoptic Area in Sleep and Thermoregulation. (n.d.). Retrieved August 2, 2022, from https://www.frontiersin.org/articles/10.3389/fnins.2021.664781/full

Gunga, H.-C. (2015). Chapter 5—Desert and Tropical Environment. In H.-C. Gunga (Ed.), Human Physiology in Extreme Environments (pp. 161–213). Academic Press. https://doi.org/10.1016/B978-0-12-386947-0.00005-8

Gjerstad JK, Lightman SL, Spiga F. Role of glucocorticoid negative feedback in the regulation of HPA axis pulsatility. Stress. 2018 Sep;21(5):403-416. doi: 10.1080/10253890.2018.1470238. Epub 2018 May 15. PMID: 29764284; PMCID: PMC6220752.

Ingersoll, G. (n.d.). 23 Examples Of Sleep In A Combat Zone. Business Insider. Retrieved August 12, 2022, from https://www.businessinsider.com/heres-23-examples-of-sleep-in-combat-2013-3

Okamoto-Mizuno, K., & Mizuno, K. (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology, 31(1), 14. https://doi.org/10.1186/1880-6805-31-14

Osilla, E. V., Marsidi, J. L., & Sharma, S. (2022). Physiology, Temperature Regulation. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK507838/

Russo, S. J., Murrough, J. W., Han, M., Charney, D. S., & Nestler, E. J. (2012). Neurobiology of Resilience. Nature Neuroscience, 15(11), 1475–1484. https://doi.org/10.1038/nn.3234

Thermoregulation in Humans—Body Temperature Regulation at Night. (n.d.). Retrieved August 2, 2022, from https://www.sleepadvisor.org/thermoregulation/

Toenders, Y. J., Laskaris, L., Davey, C. G., Berk, M., Milaneschi, Y., Lamers, F., Penninx, B. W. J. H., & Schmaal, L. (2021). Inflammation and depression in young people: A systematic review and proposed inflammatory pathways. Molecular Psychiatry, 1–13. https://doi.org/10.1038/s41380-021-01306-8

About the author:

Melanie began attending Harvard in 2020 to complete a Graduate Certificate in Human Behavior with a specialization in Neuropsychology. Boling’s research has examined extreme environments and how they can have a potential negative impact on humans operating in the extreme environment. During her time at Harvard, she has built a mental wellness tool called a psychological field kit. Implementing these tools will allow an individual to thrive in an extreme environment while mitigating negative variables such as abnormal human behavior which can play a role in team degradation.