Body and thinking
Lesson 15 of 31 in the course “Brain Hacks”. Free, with animations and a quiz.
The body affects thinking. But how much?
A hungry person is grumpier, a tired one thinks worse, and after a good night’s sleep problems get easier. Everyone knows this, and science confirms it. But a whole genre of advice grew on top of this truth: strike a superhero pose and you’ll be more confident, hold a warm cup and you’ll be kinder to people, clamp a pencil in your teeth and you’ll feel happier. Sounds like free life hacks. This lesson goes through them one by one. Spoiler: the simplest, most boring things like sleep and food work reliably, while the flashiest tricks almost vanished when tested.
A pencil in your teeth
A classic 1988 study: people held a pencil in their teeth, so their face fell into a smile without them noticing, or in their lips, producing something like a frown. The “smilers” found cartoons funnier. Everyone loved the idea: the body tells the brain what it feels. In 2016, 17 labs repeated it under one plan and found almost no effect. In 2022, a large international test showed that when people smile on request, their mood rises a tiny bit, but the pencil version works weakly or not at all. Label: disputed. A link between face and feelings seems real but tiny. A smile won’t replace a reason to smile.
The superhero pose
A 2010 study claimed that two minutes in a “power pose”, hands on hips or feet on the desk, raises testosterone, lowers the stress hormone and makes people bolder with risk. A talk about it became one of the most popular online, and millions struck the pose before job interviews. In 2015 the study was repeated with 200 participants, four times the original. Hormones didn’t change, and neither did risk-taking. People only said they felt a bit more confident. And in 2016, one of the original authors publicly wrote that she no longer believes in the effect. Label: failed to replicate. If the pose perks you up, go ahead, but don’t expect a hormonal miracle.
Hot coffee and warm feelings
Another popular story. In a 2008 study, an assistant in a lift asked participants to hold their coffee cup for a second, either hot or iced. Then the participant read a description of a stranger. Those who had held hot coffee supposedly rated the stranger as “warmer” and friendlier. A lovely metaphor: physical warmth turns into emotional warmth. The advice “give the other person a hot drink” spread through articles on negotiation and dating. In 2014, researchers repeated the study in several labs with hundreds of people. They found no effect. Label: failed to replicate. Treating someone to coffee is still nice, just not because of the temperature.
“Hungry judges”
A famous 2011 study analysed judges’ parole decisions in Israel. At the start of a session and right after a food break, about 65% of cases were decided in the prisoner’s favour, and by the end of each stretch the share fell almost to zero. The conclusion went global: a hungry judge is harsher. But critics noticed something important: cases weren’t heard in random order. For example, prisoners without a lawyer more often came last, and their chances were lower anyway. Besides, the effect is far too huge for something as small as a snack. Label: disputed. The broader idea, that fatigue at the end of a long series of decisions pushes people toward the easiest option, is supported by other data too.
What definitely works: sleep
Now for the boring but reliable part. Sleep isn’t a pause; it’s the brain at work: during sleep, what you learned during the day gets consolidated. Hundreds of studies confirm it. Lack of sleep hits attention, memory and mood. One well-known study found that after 17–19 hours awake, people performed on reaction and attention tests roughly as they did after a small dose of alcohol. And the tired person is usually sure everything is fine: the autopilot is bad at noticing its own fatigue. Label: solid. If you’re choosing between an extra hour over your notes at 3 a.m. and sleep, sleep almost always pays off more for the exam.
Hack: change your state for real
Instead of poses and cups, use what really changes your body’s state. Stuck on an idea? Go for a walk: in 2014 experiments, people came up with noticeably more creative options while walking, about 60% more on average, than while sitting. These are a few experiments by one team, so treat it as a nice bonus, not a law. Big decision? Eat first: hunger makes you irritable and impatient. Exam tomorrow? Go to bed instead of staying up till morning. Before hard tests, Danya used to drink an energy drink and sit up until four. Now he goes to bed at midnight, reviews the key points on a morning walk, and his grades have become steadier.
Try it: a check before deciding
There’s a simple check, created for people recovering from addiction, that works great for any decision. It’s called HALT: hungry, angry, lonely, tired. Before an important step, sending a harsh message, buying something expensive, quitting a project, run through these four. If even one answer is “yes”, the decision can wait. First eat, cool off, talk to someone, sleep. Danya set himself a rule: no purchases over $50 and no replies to unpleasant messages after midnight. In a month, he never once regretted putting something off.
Check yourself
- Two minutes in a “power pose” supposedly changed hormones. What did the 200-person replication show?
Correct answer: Hormones didn’t change. Yes. Neither hormones nor risk-taking changed, and one of the original authors later disowned the conclusion. - “Hold a hot coffee and you’ll feel warmer toward a person.” What’s its status?
Correct answer: Failed to replicate in large repeats. Yes. In 2014, several labs repeated it with hundreds of people and found no effect. - Why did the “hungry judge is harsher” conclusion get a “disputed” label?
Correct answer: Cases weren’t in random order, and the effect is too huge. Yes. For example, prisoners without lawyers more often came last, and their odds were lower anyway. A snack hardly turns 65% into zero. - Danya has been awake 18 hours and is stuck on a project idea. What best follows this lesson?
Correct answer: Sleep, then think it over on a morning walk. Yes. Sleep reliably restores attention and memory, and walking may add ideas.