How the heat affects our brains

The hotter it gets, the more our brains seem to slow down, and research supports this belief

Man, it’s a hot day.

And that could mean bad news for your performance at work or school, according to at least four recently published studies.

The reports, which examine the effects of air temperature on cognitive performance in the US and China, rely on different data sets and methods to arrive at the same conclusion: The hotter it gets, the more our brains seem to slow down.

The good news? These effects can be mitigated by air conditioning. But access to air conditioning is dependent in large part on economic factors. And thanks to climate change, rising temperatures in coming years are likely to place even more stresses on kids’ — and adults’— cognitive abilities.

Too hot to get good grades

The first batch of results comes from a working paper published by the US National Bureau of Economic Research. A team of American and Chinese researchers looked at the effect of average daily temperature (that is, high temperature plus low temperature, divided by two) on Chinese students’ scores on the National College Entrance Exam, a high-stakes standardised test that is “almost the sole determinant for college admission in China,” per the researchers.

Pairing millions of test results with local meteorological data for the days students took the exam, they found that, overall, every temperature increase of 3.29 degrees Celsius reduced students’ scores on the exam by 1.12 per cent, reducing their odds of getting into the most selective colleges by 1.97 per cent.

Chinese authorities are, in fact, well aware that ambient temperature can affect students’ test scores: Citing Chinese media reports, the study authors note that the use of air conditioning on testing days in some regions is prohibited “in order to ensure fair competition with regions in which AC is not available.”

Sweating away PSAT scores

As it turns out, that’s a common thread running through all these studies: Air conditioning can eliminate the effects of heat on testing performance entirely.

Earlier this year, a different team of researchers ran a similar inquiry on the effect of heat exposure on American students’ PSAT scores (the a standardised test targeting 10th and 11th graders across the US). Rather than the average temperature on test day, these researchers were interested in how the cumulative number of hot days before the test might affect students scores.

“Hotter school days in the year prior to the test reduce learning, with extreme heat being particularly damaging and larger effects for low income and minority students,” they found.

“…Without air conditioning, each 1 degree Fahrenheit increase in school year temperature reduces the amount learned that year by 1 per cent”.

Reduced learning

That’s a staggering finding: All other things being equal, in the absence of air conditioning, a slight increase in school-year temperature can reduce the amount of material learned by students.

The correlation is so strong it even shows up plainly on a US map: in the figures below from the paper, the county-level distribution of 32.2-degree Celsius days bears a striking resemblance to the distribution of PSAT scores.

Generalising outward from these data, the authors think that if heat can lower test scores, it can reduce overall worker productivity as well. “Heat exposure can reduce the rate of learning and skill formation, thus potentially reducing the rate of economic growth,” they conclude.

Brain melt

Moving slightly out of the standardised testing realm, last month, a team of Harvard researchers published the results of a unique study that monitored the cognitive performance of a group of young adults during a heat wave in Boston in summer 2016.

Similar to the studies above, the researchers found that as the mercury rose, the subjects’ performance fell on a battery of self-administered tests involving attention, cognitive speed and basic mathematical skills.

Stroop test

The plot above, for instance, shows performance on what’s known as a Stroop test, which asks subjects to parse the difference between incongruently labelled colour/word pairs. The warmer it got indoors, the harder that task became.

Dividing the subjects by whether they had air conditioning in their building of residence, the researchers found that a lack of AC was associated with a performance decline between 4.1 and 13.4 per cent, depending on the test. Because the subjects were all healthy, young, college-aged individuals, the authors noted that there’s a real possibility that deficits could be even worse among less healthy or less educated groups.

Graduation grief

Back to the classroom now: A March working paper by Jisung Park of Harvard University and the University of California at Los Angeles examined the effects of outdoor air temperature on a million New York City public high school students’ performance on the New York State Regents Examinations, a standardised test required to graduate from high school.

Again, the effects are large: Park found that “taking an exam on a 90 degree Fahrenheit [32.2 degrees Celsius] day reduces performance by 14 per cent of a standard deviation relative to a more optimal 72 degree F day”.

In Park’s sample, nearly one in five students experienced temperatures of 32.2 degrees Celsius or greater on exam day.

Because the exams are a prerequisite for graduation, heat exposure during the exams also has a direct effect on students’ odds of graduating.

Cause and effect

“For the median student, taking an exam on a 90 degree Fahrenheit day leads to a 10.9 per cent lower likelihood of passing a particular subject (e.g., Algebra), which in turn affects probability of graduation,” Park writes.

Administering the tests during the winter or spring, rather than at the end of the school year, would be one way to lessen the effect of heat on students’ scores. Air conditioning is the other — but data collected by Park shows that 38 per cent of New York City public schools lacked air conditioning equipment in 2012.

— Washington Post

It’s more than just a state of mind

Sunny and hot is better than hot and humid. True or false?

Turning to mood, studies show that warmer temperatures, particularly ones higher than expected, are associated with greater levels of happiness and wellbeing. However, once again, it’s not temperature alone that’s making a difference. Studies in Canada, Taiwan, Australia and the UK have shown that higher humidity makes us feel gloomier, sleepier and more cynical, whereas more hours of sunshine are associated with greater happiness and optimism.

In field studies, Michael Cunningham at the University of Louisville, Kentucky, US, noted that on sunnier days, people were more likely to assist him when he asked them for interviews, and when dining out, they were more likely to tip waiters generously.

So, when it’s hot and humid, you’ll find it harder to learn new material or to think logically, and you won’t feel like making complex decisions.

However, if it’s hot, especially if you didn’t expect it to be, and also sunny and dry, you’ll feel happier and more optimistic, and you’ll find it easier to be helpful and generous towards others.

You think less clearly when feeling hot. True or false?

Perhaps we’re aware of the adverse effect of hot weather on our ability to think clearly and, as a result, we avoid making challenging decisions on those days. To see if this might be true, Amar Cheema and Vanessa Patrick at the Universities of Virginia and Houston in the US tabulated the sales of different types of lottery tickets in St Louis, Missouri, for one year.

Here’s what they found:

Sales of lottery tickets were unaffected by a rise in temperature, whereas sales of scratch tickets, which demand a number of decisions to be made, fell by $594 with every one degree (Fahrenheit) rise.

Intrigued, they set up two experiments. In one they asked participants to proofread an article, and in another they were asked to choose between two types of mobile phones, a traditional model or a new, more innovative iteration. Under warmer conditions, participants made more mistakes when proofreading, and chose the phone they were familiar with over the one that required new learning.

Humidity’s the culprit; not the heat. True or false?

In a study conducted in India, V.M. Sharma and colleagues at Aimil Geotechnical Consultancy in New Delhi asked participants to take bouts of exercise, and then to perform tests of mental alertness, associative learning and problem solving in temperatures varying between 25 degrees Celsius to 35 degrees Celsius. 
Here’s what they found:

Performance dipped as the temperature rose.

However, this effect was much more pronounced when the humidity was also high.

Other research — for example, a study led by Margaret Allen and Gloria Fischer at Washington State University — shows that temperature alone has less effect on cognitive performance than when it is coupled with high humidity.

— The Telegraph Group Ltd, London 2018

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