Too Hot to Function: The Truth Behind Temperature and Cognition

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Have you ever experienced mind-numbing cold?  Or have you ever felt like it was so hot you could barely think?  Believe it or not, these expressions are more than just idioms. Research shows that shifts in core body temperature caused by extreme heat or cold can have significant effects not only on mood but also on cognition.

Cognition is the process of thought that controls how we react to our surroundings and is also our ability to store memories and perform mental tasks such as arithmetic. It can decline as core body temperature deviates from the normal measures. Extreme temperatures or long exposure to less than ideal weather can change core body temperature and impact homeostatic control, or the body’s ability to maintain its temperature. As the body works harder to maintain a healthy core temperature by reallocating resources like water and energy, the brain is deprived of these same resources and one’s ability to think declines.

The most serious heat-related issue affecting cognition is dehydration. As temperature increases, the body uses sweating as a mechanism to stay cool. Sweating results in water loss, and can potentially cause dehydration. Dehydration, a phenomenon caused by losing more fluid than one consumes, has a fairly significant effect on cognition.  Fluid is paramount in many physiological processes including but not limited to the circulation and uptake of nutrients into cells, which may explain the lack of function on a cellular level. While it is unclear exactly what mechanism ties dehydration to impaired cognition, research has shown that there is a noticeable effect.  In a study performed at the University of Georgia, Athens, researchers induced dehydration in participants by withholding water during a two-hour cycling session. After the two-hour period, the participants’ cognitive states were immediately assessed using computer-based tasks that tested short-term memory and the ability to switch focus between stimuli. The same group of men completed the same two-hour bike challenge while receiving sports drinks containing electrolytes every fifteen minutes.  The cognitive task performance scores improved significantly between the trials in which the participants were dehydrated and the trials in which the participants were given electrolyte beverages [1]. When dehydrated, the subjects were not able to remember things as well and had difficulty switching attention from one task to another.  According to this research, the brain appears to need proper hydration to function at top capacity.

Furthermore, studies have shown that as the temperature falls, core body temperature can fall, which negatively affects cognition. Researchers at Kent State University submerged subjects in 13°C  (55°F) for 30 minutes. After this step, most had core body temperatures in the range of 35 to 36°C (95-96.8° F), which is considered below the normal range of 36.5-37.2° C (97.8-99° F) [2]. The subjects rested for 15 minutes, and then researchers asked them to perform the Stroop test.  The Stroop test involves looking at the name of a color (e.g. “green”) and saying the color of the font, which is a different color than word spells.  Participants are asked to give the color of the font as fast as possible. High speed and accuracy yield high scores. The Stroop test was significantly more difficult for subjects placed in cold water than control subjects placed in neutral water [3]. This study suggests that low core body temperature has a significant effect on attention to detail, which is considered a marker of cognition.

So how can you keep your brain functioning at the highest caliber on even the hottest or coldest of days? Avoiding dehydration on hot days by consuming liquids is paramount, especially those containing electrolytes, like sports drinks or coconut water. Electrolytes, minerals such as salt and potassium, are essential for normal bodily function [4]. Additionally, avoiding caffeine and alcohol can prevent dehydration. Caffeine and alcohol are both diuretics, drugs that act on the body by increasing urine volume and consequently decreasing hydration [5].

Maintaining a high core body temperature is equally important. Just as the brain tells the body to sweat to lower core body temperature when it is too high, the brain similarly tells the body to shiver to maintain a high enough core temperature in the cold. Shivering stimulates the muscles, which causes the body to warm. However, shivering requires proper calorie intake, and the brain is not as efficient at warming the body when not enough calories are consumed [6]. Eating a balanced diet is an easy way to keep cognition strong by keeping core temperature up when the days get frosty.

Dressing appropriately for the weather is a must in preventing core temperature from dropping too low. Urban legend has led many to believe that most heat is lost through key body parts: the head, the chest, and the feet. These areas are much more sensitive to changes in temperature than other parts of the body, which has led many to believe these areas lose more heat [7]. However, instead of which body parts are exposed, the amount of skin exposed is much more important when conserving heat. Covering as much skin as possible on blustery days is the most effective way to stay warm.

Research has time and time again shown that the phrase “brain freeze” is much more than a colloquialism. Weather does in fact have a significant impact on cognition. Both extreme heat and cold can impair the brain’s ability to form new memories, retrieve memories, pay attention to multiple stimuli or switch attention between stimuli, and perform basic tasks. To keep your brain in its best shape, remember to pay attention to the weather, and keep your core body temperature as close to normal regardless of how blustery it gets. After all, a healthy brain is a sharp mind!

References

1. P.D. Tomporowski, Beasman, K., Ganio, M.S., and Cureton, K. 2007. “Effects of dehydration and fluid ingestion on cognition,” International Journal of Sports 28: 891-6.
2. “Vital Signs.” Accessed August 8, 2011. http://medicalcenter.osu.edu/patientcare/healthcare_services/emergency_services/non_traumatic_emergencies/vital_signs/Pages/index.aspx
3.  Y. Seo, Kim, C.H., Ryan, E.J., Gunstad, J., Glickman, E.L., and Muller, M.D. 2013. “Cognitive Function During Lower Body Water Immersion and Post-Immersion Afterdrop.” Aviation, Space, and Environmental Medicine 84:921-6.
4. “Electrolytes.” Accessed August 6, 2011. http://web.pdx.edu/~sujata/FruitEze/education/laxative/electrolytes.html
5. Stookey, J.D. 1999. “The diuretic effects of alcohol and caffeine and total water intake misclassification,” European Journal of Epidemology 15:181-8.
6. Olsen, Hanna Brooks. 2011. “Do You Burn More Calories in the Cold?” Huffington Post, November 16. Accessed October 3, 2013. http://www.huffingtonpost.com/2011/11/16/calories-cold-weather_n_1096331.html
7. Sample, Ian. 2008. “Scientists Debunk the Myth that you Lose Most Heat Through Your Head.” The Guardian, December 17. Accessed October 3, 2013. http://www.theguardian.com/science/2008/dec/17/medicalresearch-humanbehaviour

Sydney Reitz is a third-year student at the University of Chicago majoring in Comparative Human Development in the pre-medical track. Follow The Triple Helix Online on Twitter and join us on Facebook