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Winter Wakes Up Your Mind--and Warm Weather Makes it Harder to Think Straight

How temperature shapes difficult decisions
concentration, hot weather, man sweating, wiping off sweat



iStock / Suzanne Tucker

Imagine you are on vacation and find yourself running low on a few necessities. You stop by a small convenience store to stock up and are immediately faced with the usual suspects: cramped aisles lined with chips and candy, a “beer cave” in the back, an oddly placed rack of discount t-shirts…and a lottery showcase behind the counter—a veritable gambler’s paradise. Normally you wouldn’t play; today, however, you’re overcome by the urge to try your luck. But what game do you choose? Do you select among the dozen or so varieties of scratch tickets? Or do you opt for the classic pick-6 lotto?

Your decision may depend on whether you’re vacationing in Juneau, Alaska or Jupiter, Florida—and it all comes down to temperature. Recent research suggests that warm weather impairs our ability to make complex decisions—and even causes us to shy away from making these decisions in the first place.

In the sweltering heat of a Florida summer, choosing between dozens of scratch tickets may seem like an insurmountable task—and one you’d rather not make, given the alternative of a relatively simple pick-6 lotto (just grab a ticket, write down a few numbers, and you’re done).  In the cooler climes of Alaska, on the other hand, your ability to make complex decisions—such as choosing your favorite scratch ticket—should be unaffected.  These differences may have profound effects on your path to instant fortune.  In cooler weather, you are able to weigh your options and choose the best one, no matter how cognitively complex the decision may be; in warmer weather, however, you’re more likely to take the easiest available route—in this case, the pick-6 lotto (which, in Florida, has an approximately 1 in 22,957,480 chance of winning the jackpot).

Although the idea that our decisions are swayed by the temperature of our surroundings may seem far-fetched, consider one simple fact: our brains are organs. And, just like all other organs, these decision-making centers need energy to function. Almost everything we do—whether it is a physical behavior or a mental process—uses the same energy source: glucose. We use glucose as we walk, talk, breathe, and perform other physical functions in our daily lives. We also use glucose when we perform effortful mental functions, such as making decisions, exerting self-control, suppressing emotional responses, and even answering math problems.  Crucially, glucose—this fundamental source of both physical and mental energy—is a limited resource.

One of the body’s most important tasks is temperature regulation. When the ambient temperature is unusually hot (Florida) or unusually cold (Alaska), we must use energy—in the form of glucose—to maintain a healthy internal temperature; we shiver and sweat, seeking to avoid hypothermia and heat stroke. These two processes—correcting for excessive heat and unwanted cold—are not equally taxing, however; cooling the body down seems to require more energy than warming it up.

Warm temperatures, then, are more likely to deplete our resources—as our bodies work to maintain homeostasis, we use up large amounts of glucose. Because glucose is also used for mental processes, it may be that the physical demands imposed by excessive warmth reduce our capacity for cognitive functioning, thereby adversely affecting our decision-making abilities.

This possibility intrigued two researchers—Amar Cheema of the University of Virginia and Vanessa M. Patrick of the University of Houston—so they carried out an innovative study of real-world behavior: they gathered sales data for various types of lottery games in St. Louis County for a full year, then looked for differences in sales patterns as a function of each day’s temperature. The results were striking. Sales for scratch tickets, which require buyers to choose between many different options, fell by $594 with every 1° Fahrenheit increase in temperature. Sales for lotto tickets, which require fewer decisions on the part of the buyer, were not affected.

The researchers decided to test this apparent link between weather and complex decision-making in the lab by performing a series of experiments comparing participants’ cognitive performance at two seemingly unremarkable temperatures: 67° and 77° Fahrenheit. People tend to be most comfortable at around 72° Fahrenheit, so each temperature represented just a 5° deviation from maximum comfort.

Despite this minimal deviation in temperature, the researchers found remarkable differences in cognitive functioning. In one lab study, participants were asked to proofread an article while they were in either a warm (77°) or a cool (67°) room. Participants in warm rooms performed significantly worse than those in cool rooms, failing to identify almost half of the spelling and grammatical errors (those in cool rooms, on the hand, only missed a quarter of the mistakes). These results suggest that even simple cognitive tasks can be adversely affected by excessive ambient warmth.

In a second study, the researchers showed similar effects for more complex cognitive calculations. In this study, another group of participants were asked to choose between two cell phone plans, again in either a warm or a cool room. One plan looked more attractive on the surface, but was actually more expensive; simple patterns of decision-making would therefore lead participants to choose the more expensive plan, whereas more complex analyses would lead participants to correctly choose the more cost-effective plan. Participants in the cool room made the correct choice over half the time; those in the warm room, on the other hand, made the correct choice only a quarter of the time. Warmer temperatures seemed to make participants more likely to rely on simplistic patterns of decision-making, which in turn led to inferior choices. These results suggest that complex decision-making, like simple cognitive tasks, is adversely affected by warm temperatures.

A third study suggests that warm surroundings may not just cause people to fail at complex decision-making—it may cause them to shy away from making these sorts of decisions in the first place. In this study, participants were placed in either a warm or a cool room and asked to choose between two products: an innovative one and a traditional one. Participants in warm rooms, relative to those in cool rooms, were much more likely to choose the traditional product—ostensibly because they did not have the cognitive resources necessary to evaluate the new information relevant to an innovative item.

Of course, demonstrating temperature-related differences in cognitive functioning does not necessarily mean that these differences are due to depleted glucose supplies. Nor does it rule out the possibility that these effects are driven by improvements in cognitive ability under cooler conditions (as opposed to impairment under warmer conditions). With these alternate interpretations in mind, the researchers added one crucial component to each study: they depleted glucose supplies for half of the participants before placing them into warm or cool rooms, and left the other half undepleted.  Participants in warm conditions behaved almost exactly like pre-depleted participants; this suggests that warm temperatures result in natural resource depletion, which in turn impairs cognitive functioning.

Taken together, these studies suggest that higher ambient temperatures change our patterns of decision-making. As our bodies struggle to maintain a healthy internal temperature, they use up resources that would otherwise be available for mental processes. As a result, we are less able to make complex decisions—we give up early, make mistakes, and even shy away from making these decisions in the first place. We choose the easy option—a standard, one-option lotto game—rather than the complex one—selecting one out of dozens of scratch tickets.

These results do not mean, however, that people in warmer climates are reliably prone to making poorer decisions than those in cooler environments. Human beings are remarkably adaptive; we automatically acclimate to changes in ambient temperature and—given a bit of time—are capable of performing just as well in sweltering heat, frigid cold, and a climate-controlled office. It really does matter that you were on vacation when making your lottery decision; if you had been a native Alaskan or Floridian, the temperature would have made little, if any, difference. This research suggests that what does make a difference is slight deviations in temperature from an expected norm. Even though an unusually warm day in northern Alaska may be 50° cooler than such a day in the middle of Florida, the effect on cognitive processes may be the same.

These slight deviations in temperature are a common part of our lives—the warmth of our homes and offices fluctuate throughout the day, stores and restaurants seem to set their thermostats with little regard for human comfort, and temperatures outdoors vary not just from day to day, but from minute to minute. Each of these minor changes in temperature may have important implications for our ability to make decisions, especially when we are unaware of these effects—but, luckily, now you are aware.

Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist at the Boston Globe. He can be reached at garethideas AT gmail.com or Twitter @garethideas.

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