Too hot to handle
Thermal strain - are you cool-headed or warm-hearted? (Repost)
(given the extremes of heat being felt here in Europe atm, I thought this would be a good repost for newer readers)
Keeping with recent themes regarding our metabolism, I thought it would be fun to look at the effects of environmental heat on our cognitive and social functioning.
One punchline you’ll know already: extremes of heat are very bad for your brain, and hence your general cognitive functioning.
Another punchline is one you’ll have an opinion on: that there is some association between high temperatures and antisocial behaviour (the ‘heat-facilitates-aggression’ hypothesis). You might be wrong in what you think though.
The final punchline tests a newer idea: that warmth or higher temperatures are linked in some way to doing nice things for others (the ‘warmth-primes-prosociality’ hypothesis). You might be wrong in what you think here, too.
steampunk painting antisocial behaviour prosocial hot cold
For a quick primer on our metabolism (inc heat) see below:
‘Eat less, exercise more’ is useless advice; Our activity levels are up.
Maintaining core temperatures takes work
As warm-blooded creatures, we humans (like all mammals), work to maintain a stable core temperature of around 37°C (98.6 F; although, as the link above shows, this has been trending down for a while). This is called ‘temperature homeostasis’, and is a fundamental physiological function that helps to keep our body temperature within a narrow range. Our receptors are in constant communication with the external environment, providing the feedback necessary to maintain a stable core body temperature.
When we become too hot, our body responds by redirecting blood flow to the surface of the body (vasodilation). This process helps to radiate heat away from the body trunk and the brain, and we also cool through perspiration.
Fun fact: very few species perspire to cool down. But we humans do. Humans are great ‘persistence hunters’, because a group of us can take turns running and walking large animals down - they eventually have to cool down by stopping and breathing to cool down1.
When we’re too cold, our body responds by constricting blood vessels in the periphery of the body (vasoconstriction) and we may shiver in an attempt to generate heat. You’ll possibly have read that taking cold showers is health-promoting, for various ill-explained reasons. You might even have heard that lots of cold showers help burn body fat. Don’t believe this. The data are really thin. Honestly.
If you enjoy a cold shower - go for it. But don’t suffer. Go for a good stiff walk instead - it’ll do you more good.
We humans also uniquely regulate our body temperature by donning or removing clothing. This helps us regulate temperature and maintain temperature homeostasis, despite variations in external temperature.
Temperature homeostasis is involuntary: all mammals, including humans, engage in it. For example, when dogs pant on a hot day, they are engaging in a process similar to sweating that helps to maintain their body temperature. Similarly, when a polar bear curls up into a tight ball to conserve heat, it is engaging in temperature homeostasis to maintain a stable core body temperature in the frigid Arctic environment.
Heating the brain is bad for brain function
Simmons and colleagues investigated the effects of passive heating and head cooling on perception, cardiovascular function, and cognitive performance in the heat2. These experiments were cleverly designed to separate increases in skin temperature from increases in core body temperature, to understand how these factors influence perceptions of heat-related fatigue and cognitive function3.
Volunteers wore a special balaclava made of plastic allowing water at 3°C to be circulated through it, cooling effectively head and neck. The volunteers were then exposed to a temperature of 45°C in a climactic chamber until their core body temperature increased by 1°C. They also completed a battery of cognitive tests multiple times.
High body temperatures, skin temperatures, and core temperatures led to a significant decline in performance across all cognitive measures.
However, when the head was cooled, and the skin remained warm, core body temperature was also cooled, resulting in normal cognitive performance.
It is possible to tell the difference between the effects of inducing high temperatures in the body periphery and of inducing high temperatures in the body core: the high temperatures in the body core cause cognitive impairment. The authors say:
“...raising both skin and core temperature resulted in increases in perception of heat-related fatigue, increased cardiovascular strain, and decrements in cognitive performance....”.
They did observe one paradox of heating: simple reaction times decreased a little. However, under conditions of heat people may respond more quickly, but they do so less accurately: speed of response goes up, but accuracy goes down. It is a well-observed phenomenon that nerve conduction velocity is enhanced somewhat under higher temperatures (up to a limit), and increases in simple reaction times may result simply from faster transmission of impulses along the nerves in the periphery.
There is a reason we praise people for being cool-headed!
Excuse the interruption: for less than the price of a pizza, you can order my new book ‘Talking Heads: The New Science of How Conversation Shapes Our Worlds‘ for your Kindle, to be autodelivered on 3rd Aug for some nice summer/autumn reading (also: Amazon (UK), or Amazon.com)!
‘Talking Heads is a stunning survey of the science of human connection and communication - from neurons to nations’
Click the button to go straight to Amazon to order.
What is the relationship between general temperature and behaviour?
It’s often claimed (anecdotally, at least) there’s a link between higher temperatures and increased antisocial behaviour (aggression, violence, etc. - the ‘heat-facilitates-aggression‘ view). However, some more recent studies try to add nuance to this picture, claiming a link between higher temperature experiences and increases in prosocial behaviour (altruism, sharing, cooperative, etc. - the ‘warmth-primes-prosociality’ view).
Empirical evidence for both hypotheses has been inconsistent and inconclusive, and many studies have found mixed or opposite results. Notably, few studies take the care of Simmons et al to properly isolate temperature effects using climactic chambers, head cooling, and the like.
Happily, a recent, excellent paper comprehensively reviews both of these hypotheses.4 The authors systematically reviewed and meta-analysed studies that examined the effects of temperature on behaviour. They focused on:
Prosocial behaviour: behaviour that benefits others or society, such as giving money, gifts, or help.
Antisocial behaviour: behaviour that harms others or society, such as taking money, retaliating, or sabotaging.
They also considered different types of temperature experiences, such as:
Haptic temperature: the temperature of an object that is touched or held by the participant.
Ambient temperature: the temperature of the environment or room where the participant is located.
They also examined if the social context of the experiment influenced the effects of temperature on behaviour (e.g., if the participant interacted with a friendly, neutral, or hostile person). The analysis included 4577 participants and examined 80 effect sizes.
Conclusion:
There was no reliable effect of temperature on behavioural outcomes. There was little support for the warmth-primes-prosociality view or the heat-facilitates-aggression view. There were no reliable effects across different types of temperature experiences, or potential interactions with the experimental social context.
Those studies saying that there is a relationship between holding something warm and feeling warmth toward someone? Hmm. Seriously: hmm.
Williams and Bargh (2008) reported that holding a hot cup of coffee caused participants to judge a person’s personality as warmer, and that holding a therapeutic heat pad caused participants to choose rewards for other people rather than for themselves. These experiments featured large effects (r = .28 and .31), small sample sizes (41 and 53 participants), and barely statistically significant results. We attempted to replicate both experiments in field settings with more than triple the sample sizes (128 and 177) and double-blind procedures, but found near-zero effects (r = –.03 and .02). In both cases, Bayesian analyses suggest there is substantially more evidence for the null hypothesis of no effect than for the original physical warmth priming hypothesis. (emphasis added)
Some takeaways from all of this
Increased brain temperature is a bad thing: heatstroke is real, as are the cognitive and other effects of excessively high body temperatures - keep your head cool in hot temperatures!
Handing out cups of warm coffee to people and then hoping they’ll be nice to you is a forlorn hope. The bank manager will still foreclose your unpaid mortgage, even if you bring him a nice Flat White.
Effects of general temperatures on mood and behaviour might depend on other factors, such as expectations, cultural norms, and individual differences: some people enjoy hot weather more than others, and some cultures have rituals or customs that mitigate the negative effects of heat.
We deliberately consume cold drinks (often made with alcohol) to foster communal feelings: going for a cold beer when it’s very warm is great. But we wouldn’t bother if the ambient temperature was making us feel prosocial anyway!
Furthermore - there is no real effect of general temperature increases on aggression or on pro-social behaviour. Why? Most probably because our brain and body work to keep our temperature down - so there is an immediate confound present in such studies.
Moreover, any effects of temperature on mood and behaviour might change over time, as people adapt to their environment and learn to cope with heat or cold: people might develop strategies to regulate their emotions or seek social support when they feel uncomfortable due to the temperature.
We humans have adapted to every variation of environmental temperature range on the planet. If ambient temperature so easily turned us from rage to empathy we’d have a problem.
Or we can simply turn the AC on.