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In the mid-1990s, Roy Baumeister, Ph.D., a social psychologist who at the time was teaching at Case Western Reserve University, revolutionized how we think about the mind and its capacity. Baumeister wanted to get to the bottom of common-day struggles such as why we feel mentally “tired” after toiling away at a complex problem. In other words, Baumeister was interested in understanding how and why our intellectual power and our willpower run out of gas.
“The only person you are destined to become is the person you decide to be.” – Ralph Waldo Emerson
Experiment with Cookies & Radishes
When Baumeister set out to solve this problem, he didn’t need the latest and greatest brain-imaging technology. All he needed were some cookies and radishes.
In an elegantly designed experiment, Baumeister and his colleagues had 67 adults file into a room that smelled like chocolate chip cookies. After the participants had taken their seats, freshly baked cookies were brought into the room. No sooner than everyone’s salivary glands began working, things got interesting. While half the study participants were allowed to eat the cookies, the other half were prohibited from doing so. Adding insult to injury, the non-cookie-eaters were given radishes and told they could eat them instead.
As you might imagine, the cookie-eaters had no problem with the first part of the experiment. Like most people in their situation, they enjoyed indulging. The radish-eaters, on the other hand, struggled mightily. “The [radish-eaters] exhibited a clear interest in the cookies, to the point of looking lovingly at the display and in a few cases even picking up the cookies to smell them,” writes Baumeister. Resisting the cookies was no easy task.
Second Part of Experiment
This doesn’t seem groundbreaking. Who wouldn’t struggle to resist delicious desserts? But things got even more interesting in the second part of the experiment, during which the radish eater’s struggles continued. After both groups finished eating, all participants were asked to solve a seemingly solvable, but actually unsolvable, problem. (Yes, this was a cruel experiment, especially for those stuck with the radishes.)
The radish-eaters lasted a little over 8 minutes and gave the problem 19 attempts. The cookie-eaters, on the other hand, persisted for over 20 minutes and attempted to solve the problem 33 times. Why the stark difference? Because the radish-eaters had depleted their mind muscle by resisting the cookies, whereas the cookie-eaters had a full tank of psychological gas and thus applied far more effort in trying to solve the problem.
Baumeister went on to repeat several variations of this study, and he observed the same result every time. Participants who were forced to stretch their mind muscle—be it to resist temptation, solve a hard puzzle, or make tough decisions—performed worse on a subsequent task that also required mental energy as compared to participants in a control group who had an easy first task, like eating fresh cookies.
Resisting Cookies Is A Dangerous Game
It seems we have a single reservoir of brainpower for all acts of intellect and self-control, even those that are unrelated. When people are asked to suppress their emotions when under pressure—for example, not showing frustration or sadness while watching a tragic film—they subsequently struggle with a wide range of unrelated tasks, such as resisting mouth-watering foods or storing items in working memory. The phenomenon doesn’t stop there. Even physical challenges (e.g., performing a wall sit) can be weakened in this process. Research shows that even if their bodies are fresh, the physical performance of people who are mentally fatigued suffers. Put differently, the boundaries between mental and physical fatigue are not nearly as defined as we think.
In a study cleverly titled “Hungry for Love: The Influence of Self-Regulation on Infidelity,” 32 college students in exclusive relationships interacted via chat room with a partner (i.e., a researcher playing along) of the opposite sex. Prior to this chat, half the study participants were forced to resist eating mouth-watering food, while the other half could eat to their hearts’ desire. As you might expect, those who were forced to resist the tempting food were more likely to give their phone number to, and even accept a coffee date with, the partner. The study authors concluded, “Weakened self-control may be one potential cause for the levels of unfaithfulness occurring in romantic relationships today.”
A Look Inside Your Tired Brain
More recently, researchers have started studying the notion of a mental muscle with fancy imaging technology instead of just cookies and radishes. What they are finding is quite fascinating. They put people with depleted mental muscles in an fMRI machine (a technology that lets researchers look at activity inside the brain) and discovered the brain of a tired person acts in a peculiar way. When shown a tempting image, such as a juicy cheeseburger, or asked to solve a hard problem, activity in parts of the brain associated with emotional response supersedes activity in the part of the brain tasked with thoughtful, rational thinking. It’s no wonder that when we are mentally drained we struggle with complex problems and self-control, opting for cartoons and cookies instead.
Way Ahead
Much like how after you’ve lifted weights to the point of fatigue your arms won’t function very well. But once arms recover from fatigue, they actually strengthen. The good news is that just like the body, by stressing and allowing the mind to recover it also becomes stronger. Scientists have discovered that the more we resist temptation, think deeply, or focus intensely, the better we become at doing so.
A new line of research contests that willpower in particular is not as limited as scientists once thought, and suggests that by successfully completing smaller productive changes we can build the strength to complete larger ones in the future. Either way, whether it is the result of willpower, ego depletion, or some other mechanism, we cannot continuously use our mind (at least not effectively) without at some point experiencing fatigue. And we cannot take on more sizeable psychological challenges without first building strength through smaller ones. All of this takes us to the formula of mind growth: stress + rest = growth. (Excerpt is from “Peak Performance: Elevate Your Game, Avoid Burnout, and Thrive with the New Science of Success” by Brad Stulberg).
