-- From the Amygdala to the Prefrontal Cortex
"Is physical activity good for depression?"
Most people would answer yes without hesitation. But research recently published by my lab tells a more complicated story. Physical activity performed at work actually increases the prevalence of depression by up to threefold as it rises. Leisure-time physical activity, by contrast, cuts the risk in half. Another of our papers found that sedentary time, too, affects mental health differently depending on the purpose. Sitting to study showed no association with depression or suicidal thoughts. But more time on mobile devices scrolling social media — especially among adolescent girls — was linked to a significant rise in depressive feelings and suicidal impulses. The value we place on a behavior changes the effect that behavior has on our health.1
How to Turn Labor into Exercise
There are two ways to make a lab mouse exercise: a treadmill and a running wheel. When researchers compared treadmill mice, running-wheel mice, and sedentary mice to see which group died first, the result was striking. The treadmill mice died earliest. Then the sedentary mice. The running-wheel mice lasted the longest.
Why?
The treadmill was never the mouse's choice. A researcher placed the animal on the belt, set the speed, and switched it on. The researcher also decided how long the mouse would run. If the mouse slowed down or tried to stop, an electric shock plate at the back of the belt was waiting. On top of that, mice are nocturnal, but the humans running the experiment worked during the day — so the mice ran on human schedules. Translate this into human terms: imagine a drill sergeant barging into your barracks at two in the morning, dragging you out to the parade ground in your underwear, and forcing you through calisthenics. Stop running and you get beaten.
The running wheel was a completely different experience. Those mice treated running as play. They decided when to start, how fast to go, and when to stop. If they felt like sprinting until they hit a runner's high, they could. If they wanted to step off the wheel before breaking a sweat, that was fine too. Run after a meal, or skip the run and sleep — the choice was entirely theirs. No electric shocks, no missed meals. In one of my own studies, mice measuring about eight or nine centimeters ran more than forty kilometers a week. That is farther than a round trip from Yonsei University's Sinchon intersection to Seoul National University at the base of Gwanak Mountain. Force them to cover that distance and running stops being exercise. It becomes *labor. And that is precisely the point: physical activity at work is labor; physical activity during leisure is enjoyment.2 Even when the movement itself is identical, what matters is whether it was your choice.
Here is another example. Say a hundred people run a marathon. Generally, the better your finish, the higher your post-race testosterone.* So does fiftieth place always produce lower testosterone than second? The honest answer is: it depends. The runner in fiftieth place might be running their very first marathon, thrilled just to have finished, and genuinely excited to learn that fifty people came in behind them. Meanwhile, the runner-up might have spent a year training obsessively with the single goal of winning — and now be crushed by falling one place short. The same physical stress, the same race, but the psychological and physiological outcomes are completely different. Context and meaning make all the difference.
Alia Crum, now at Stanford, conducted a study during her graduate years at Harvard that would have a major impact on the field. She told a group of hotel housekeepers that their daily work actually counted as exercise. She then surveyed how much exercise they believed they were getting and measured their weight and blood pressure. The housekeepers who received this reframing reported feeling like they were exercising more — and their weight and blood pressure dropped significantly. Crum then went further. She placed two groups in equally stressful situations. One group was taught that stress helps us rise to challenges. The other was told that stress is harmful and should be avoided at all costs. When she measured their hormones afterward, the group that learned to view stress as useful showed more positive emotion, greater cognitive flexibility, and elevated levels of DHEA — a hormone known to prevent depression, support immune function, and strengthen bones and muscles. The group taught that stress is purely bad showed none of these benefits. There is an old saying: "If you can't avoid it, enjoy it." These experiments suggest the proverb is scientifically sound. When we cannot escape stress, simply knowing that it can have a positive side is enough to help us handle it better.3
The brain regions that respond first to our environment are the amygdala and the hippocampus. Running raises your heart rate, quickens your breathing, and makes you sweat — physiologically, it is a significant stressor for everyone. But whether running feels good or miserable depends entirely on why you are doing it. During my military service, the mandatory group runs were excruciating. The reason was simple: I had no say in the matter, no idea when it would end, senior soldiers were cursing at me from behind if I slowed down, and the threat of ten extra laps hung over us if even one person fell back. The senior leading the run, on the other hand, was perfectly relaxed — he ran at whatever pace suited him, stopped whenever he wanted, and could head back to the barracks the moment he felt tired. The amygdala reacts reflexively to bodily signals and environmental pressures — threats, coercion, danger. But the prefrontal cortex is what provides context, assigns meaning, and allows for a considered response rather than a raw reaction.
The brain's architecture is telling. The amygdala sits right next to the hippocampus because the emotions we feel about people and situations need to be tagged and stored in memory immediately. Threatening situations, dangerous people, hazardous places — we need to remember these things to survive. Animals with damaged amygdalae cannot respond quickly to threats, and their survival rates in the wild drop sharply. Robert Sapolsky has recently reflected publicly that he spent his entire career studying stress and the hippocampus when he should have been studying the prefrontal cortex. Because ultimately, interpreting any situation in context — figuring out what it means — is the prefrontal cortex's job. The prefrontal cortex matters enormously. We need to shift from the reptilian brain to the modern human brain. You can resolve a hundred times not to lose your temper, but when the trigger comes, anger fires anyway.
Freud viewed trauma as the root of hysteria and believed that treatment required excavating the memories and emotions at its source — tracing the links between amygdala, hippocampus, and long-term memory to resolve the wound. This process, psychoanalysis, demanded long and painstaking journeys back to the original pain. Adler took the opposite approach. Reject the trauma narrative, he counseled. Look forward. His view, in a nutshell: stumbling blocks can become stepping stones.
From Freud to Adler
Let me illustrate with a figure nearly every Korean knows: Moses, the protagonist of the Disney animated film The Prince of Egypt. Moses was born a Hebrew inside the Egyptian empire. At the time, every Hebrew child under one year old was condemned to death. His mother, unable to kill her own child with her own hands, placed him in a reed basket sealed with pitch and set it adrift on the Nile. An Egyptian princess found the basket, and Moses grew up in the palace as a prince of Egypt — a dramatic reversal.
Then, around the age of forty, Moses beat an Egyptian official to death with his bare hands for brutalizing a Hebrew slave. Maybe he thought it was his destiny to stand up for his people — the self-image of a hero. But the next day, when he tried to break up a fight between two Hebrews, one of them snapped: "What, are you going to kill us the way you killed that Egyptian?" Word had already spread. Terrified, Moses ran.
He fled for days without looking back. In the wilderness he met Zipporah, married her, and had a son he named Gershom — meaning "I have become an alien in a foreign land." The name is soaked in self-pity and despair, a snapshot of where Moses' head was at. Then a second son came along. This one he named *Eliezer — "God rescued me from the sword of Pharaoh." At the time, nothing about Moses' actual situation had changed. He was still stuck in the middle of nowhere, tending not even his own sheep but his father-in-law's flock — the picture of a man going nowhere. And yet, from that same situation, he arrived at a completely different interpretation. A new context. A new meaning.
Shortly after naming his second son Eliezer, Moses encountered a bush burning on Mount Sinai — burning but not consumed — and received from that fire the immense calling to lead the Hebrew people out of slavery.
Nothing in his circumstances had changed. But the moment he reinterpreted his past, a new future came into view. At first Moses had blamed the Hebrews who did not appreciate his intentions. He had blamed Pharaoh. He had blamed God. But now he could see that every twist and disaster had been part of a larger plan — the liberation of his people from bondage. Suddenly, his future and his purpose became clear. If his first son Gershom represented a reflexive reaction to circumstances (the amygdala), then his second son Eliezer represented meaning discovered through reinterpretation (the prefrontal cortex). This was not past-oriented psychoanalytic excavation (Freud) but future-oriented reframing of the past (Adler). When Moses' narrative changed, his wife changed, his family changed, his people changed, and the course of world history changed with them.
We need to make the same shift — from Freud to Adler. Not the amygdala's reflexive firing, but the prefrontal cortex's contextual reading and meaning-making: that is what redirects our lives toward the future. Adler himself viewed his congenital disability and the constant sting of being compared to his brother as the very forces that pushed him to become a better person. Instead of thinking, "I didn't get enough love as a child, so my oxytocin is low, and that's why I can't be a good father or husband," the shift needs to go something like this: "Despite all of that — no, because of all of that — I will love my children and my spouse, and I will build a brighter, more loving home." Live the oxytocin lifestyle. Dream of a future full of love.
\* The term "runner's high" was first used by the American psychologist Mandell in a 1979 paper, describing the euphoria experienced by dedicated runners.
\* In a state of overtraining, testosterone — which normally promotes muscle growth and repair — declines, while stress hormones rise.
\* "Gershom" conveys the sense: "I am an alien in a foreign land."