In July 2016, a heatwave struck Boston, USA, with average daytime temperatures exceeding 33 degrees Celsius for five consecutive days.
High temperatures can have concerning effects on the body. (Photo: New York Times).
Some local college students who stayed in town that summer were fortunate to live in dormitories equipped with central air conditioning. However, others, not many, were stuck in older dorms without this cooling equipment.
Jose Guillermo Cedenõ Laurent, a researcher at Harvard, decided to take advantage of the situation to conduct a natural experiment to see how temperature, particularly nighttime temperatures, affected the cognitive performance of young people.
He asked 44 students to complete math tests and self-control assessments in three phases: five days before the temperature increase, each day during the heatwave, and two days thereafter.
“Many of us think we’re immune to heat,” Dr. Cedenõ stated. “So, what I wanted to test was whether that was true.”
The results indicated that even young, healthy college students were affected by high temperatures.
On the hottest days, students in the non-air-conditioned dormitory, where the average nighttime temperature was 26 degrees Celsius, performed significantly worse on tests each morning compared to those in air-conditioned rooms, where the temperature was comfortably maintained at nearly 22 degrees Celsius.
Currently, a heatwave is once again engulfing the Northeast, South, and Midwest regions of the United States.
High temperatures can have concerning effects on the body, such as increasing the risk of heart attacks and heat strokes, particularly among the elderly and those with chronic illnesses.
Moreover, as demonstrated by the experiment, heat also harms the brain, impairing cognitive abilities and making us irritable, impulsive, and aggressive, according to the New York Times.
Heat affects the brain, impairing cognitive abilities, and making us irritable, impulsive, and aggressive. (Photo: Bloomberg).
How Temperature Affects Cognition
Many laboratory studies have yielded similar results to Dr. Cedenõ’s experiment. In these studies, cognitive test scores decreased as scientists raised room temperatures.
One study found that a mere increase of 4 degrees Celsius—an increase participants reported feeling comfortable with—led to an average performance decline of 10% in tests of memory, reaction time, and executive function.
This can lead to practical consequences. R. Jisung Park, an environmental and labor economist at the University of Pennsylvania, examined standardized test scores in high school. He discovered that scores dropped by 0.2% for each degree Fahrenheit (approximately 0.56 degrees Celsius) starting from 22.2 degrees Celsius and above.
It may not sound like much, but it can add up for students who must take tests in non-air-conditioned rooms during heatwaves exceeding 32 degrees Celsius.
In another study, Dr. Park found that the more days of above-average heat during the school year, the worse students performed on standardized tests—especially when temperatures exceeded 27 degrees Celsius.
He suggested that this might be due to increased exposure to high temperatures affecting students’ learning throughout the school year.
According to Dr. Park, this effect is “more pronounced among low-income and minority students,” possibly because their schools and homes are less likely to be equipped with air conditioning.
Unusual heatwaves are engulfing many cities worldwide. (Photo: Bloomberg).
Why Does Heat Make Us More Aggressive?
Researchers first discovered the link between temperature and aggression by examining crime data. They found an increase in assaults and domestic violence on hot days.
This relationship also applies to non-violent behaviors. As temperatures rise, people are more likely to honk their horns in traffic and post hateful comments online.
Laboratory studies support this. In a 2019 experiment, compared to those in cool rooms, participants in hot rooms reacted more aggressively towards others when playing specially designed video games.
Aggressive reactions tend to be particularly sensitive to temperature. The New York Times notes that this may be because we tend to interpret others’ actions as more hostile on hot days, and react similarly.
Kimberly Meidenbauer, an associate professor of psychology at Washington State University, suggests that the increase in reactive aggression may be linked to the impact of temperature on cognition, particularly the decline in self-control.
“The tendency to act without thinking, or being unable to prevent oneself from acting in a certain way, also seems to be affected by temperature,” she said.
During hot summer days, it’s important to stay hydrated. (Photo: Bloomberg).
What’s Happening in the Brain?
Researchers do not yet know exactly why temperature affects human cognition and emotions, but several hypotheses have been proposed.
First, the brain’s resources are being diverted to keep the body cooler, leaving less energy available for other functions.
“If you allocate all the blood and glucose to parts of the brain and focus on regulating temperature, it’s very likely that you won’t have enough energy left for some other higher cognitive functions,” Dr. Meidenbauer explained.
You may also become distracted and irritable due to feeling hot and uncomfortable. It turns out that this is one of the brain’s coping responses.
If you cannot cool your body down, your brain will “make you feel even more uncomfortable, in an effort to drive you to seek what is necessary for survival more intensely,” explained Shaun Morrison, a professor of neurosurgery at Oregon Health and Science University.
The impact of heat on sleep may also play a role. In the Boston study, the hotter the weather, the more disrupted students’ sleep was—which correlated with worse test results.
The best way to mitigate this impact is to try to cool your body down as soon as possible. If you cannot use air conditioning, fans can help, and be sure to stay hydrated.
This may sound obvious, but the most important factor for your brain, mood, and cognition is your body temperature, not just the external temperature.
