Three Brain Rules You Need to Know

medina■ John Medina is a molecular biologist, private consultant, professor, Director of the Brain Center for Applied Learning Research, and, most recently, best-selling author, thanks to the runaway success of his book, Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School. Medina, who calls himself a “grumpy scientist,” wrote the book out of a desire to popularize what has been scientifically proven about the brain while dispelling popular myths.
__ “The good thing about scientific empiricism is that you can turn a guess into actual data,” says Dr. Medina. “You might have thought that people want to take a nap, but until you actually measure what the brain is doing when it wants to down-cycle in the mid-afternoon, it must remain in the realm of anecdote. I wrote Brain Rules because I got tired of hearing so much anecdote. There are too many mythologies out there, like ‘You only use 10% of your brain’—that’s a myth; ‘There are right- and left-brain personalities’—that’s a myth; ‘If you play Mozart to your baby when you’re pregnant, it’ll come out as a math genius’—that’s a myth, too.”
__ “Most of the stuff we do know about the brain has only been around for 10 years,” he explains. “Because we know, the moral exigency is now on us. We know the brain’s evolutionary performance envelope. Here it is: The brain appears to have been designed to solve problems in an outdoor setting in unstable meteorological conditions, and to do so in near-constant motion. That’s what the brain is good at doing.”
__ Dr. Medina believes that society needs to reevaluate its institutions in the light of these new insights. “If you want to design an education system that is diametrically opposed to what the brain is naturally good at doing,” he says, “you would design a classroom.” When we asked if he was trying to influence social policy, he replied, “The first step in influencing policy is data. This book is a call for brain scientists, education scientists and business scientists to get together and do experiments that could become prescriptive. Once those studies are in place, the policy almost forms around itself.”
__ To help us to set the policies for our daily lives, we asked Dr. Medina to choose the three brain rules he thinks are most important to the average person. Without hesitation, he answered: exercise, stress, and sleep.


“Exercise is extraordinarily important for executive function. When I talk to business audiences, I say that executive function allows you to design a satellite: It’s good for attention to detail, problem-solving, and mathematics. But it’s also what will keep you from punching your boss in the nose if you get a bad performance review. Executive function is involved in planning, foresight and impulse control.
__ “We know that you can increase executive function simply by aerobically exercising as little as three times a week for 30 minutes. It’s actually very specific. Toning exercise doesn’t give you a boost in executive function. Lifting weights doesn’t either. The data is so strong, we even know where the sweet spot is: Executive function starts to fly about an hour after a standard workout.
__ “A group of Siemens engineers were going to open up an office in China, and were learning Mandarin. They got a 22% increase in the rate of vocabulary acquisition if, right after their students exercised, they sat them down in the class—as opposed to control groups who had no exercise, or had exercise but did their learning in the evening. That’s extraordinary.
“In a knowledge-based economy, where executive function is one of our most important cognitive gadgets, every think tank on the planet ought to have not cubicles but a powerful set of treadmills. The business uniform shouldn’t be a suit and tie, it should be gym clothes. You should have a guided workout punctuated with meetings, emails and work. Right now we invert that: We work, and you can exercise on your own time. We have it backwards.
__ “You might have very good parents and start out with a lot of genetic horsepower. But if you become sedentary, you aren’t nearly as likely to mobilize it. There’s a specific chemical reaction that occurs in the brain when you do aerobic exercise. If you’re exercising, you increase the cerebral blood flow to the dentate gyrus, and you will produce ‘miracle grow’ for the brain—a protein called brain-derived neurotrophic factor, BDNF. The bottom line is that anybody can benefit from that, from smart guys to not-so-smart guys.
__ “Alzheimer’s and dementia can be reduced by 50%, and affective disorders like depression and anxiety can be alleviated through exercise. A study was done comparing the antidepressant medication Zoloft combined with therapy, versus therapy and exercise. The answer is astonishing: Both have an 80% success rate. They’re equally effective.
__ “I was 248 pounds when I started this book. I knew the hypocrisy meter was going to go off. So I put a treadmill in my office—I hate exercise and would IV a Big Mac if I could, to be honest—but I told myself anytime I had to check email or do data analysis, I would not sit at my desk. I will take my laptop and work out. I’m now down to 211 pounds and I’ve never felt intellectually clearer in my whole life. A treadmill is always going to be part of my desk, and I think we have to change the whole system to do that everywhere.”


“Sixty percent of all doctor visits are directly related to stress issues. Stress is an unbelievable wrecking ball in our society. My rule is: Stressed brains don’t learn the same way as non-stressed brains. What I really want to say is: Stressed brains don’t learn at all. In fact, stress causes brain damage.
__ “But there are three confounders: Not all stress is bad for learning. Nothing focuses your attention like an AK-47. But under stress conditions, blood flow is diverted to your thighs. You’ve probably heard of fight or flight—well, that’s also kind of a myth. It’s flight, period. We’ll fight if we’re cornered. Stress will focus you for a time to let you get out of Dodge—but not to do a calculus test.
__ “The second confounder is that what is stressful for one person is not necessarily stressful to somebody else. Some people love jumping out of airplanes; for others it’s their worst nightmare.
__ “Third, if you looked at the physiology workup of someone experiencing intense pleasure and someone experiencing intense stress, and asked me, ‘John, who is having an orgasm, and who is being chased by a tiger?’ I couldn’t tell you the difference. That’s why it’s so hard to do this research.
__ “Eventually, what allowed us to understand stress was the perception of control. ‘Out of control’ is measured in two dimensions; you can’t control the frequency or the severity of the adverse stimulus. The less you feel in control, the more likely you are to experience the type of stress that can hurt learning. If you feel out of control of your life, you are more likely to experience depression and anxiety disorders.
__ “The stress response was built for stresses that last no more than five minutes in duration. The saber-toothed tiger ate you, or you ran away from it. If you overlay culture and society on top of this Pleistocene brain of ours—you are in a bad marriage, or a bad job, or are being beaten up at night by a bad dad—you can have a saber-toothed tiger that’s at your doorstep not for five minutes, but for decades. We now know that type of stress causes brain damage.
__ “If you look at images of some brains, it looks like someone took a shotgun and blew away parts of their hippocampus. BDNF, which is regulated by the hippocampus, can mitigate the effects of cortisol. But if you have too much cortisol, the defenses are overwhelmed and brain damage occurs.
__ “We now know that aerobic exercise buffers against stress because it increases the amount of BDNF in the brain. That’s why we think aerobic exercise worked as well as Zoloft. But this is the good news: It is only the stressors that you believe you have no control over that cause the damage. You just have to look at those stressors you have no control over, and not focus on anything else.
__ “The first step is to make a list of the stressful things in your life, and separate the ones you can control from those you can’t. Know thy enemy. If you know what is bothering you, it produces a level of control that you did not have before. It’s just the beginning stage, but you have to know where the battleships are before you can sink them.
__ “There are two powerful palliatives. One of them is cognitive behavioral therapy—every time you have a self-defeating thought, you introduce a non-self-defeating thought and reward yourself for doing so. If you do it regularly, the self-defeating thought diminishes in power. The other is the unbelievable power of empathy—both delivering it and feeling it. There is a powerful neurobiology of empathy.
__ “Empathy has three requirements: One, you have to be able to detect an affective change in somebody else. Autistic kids can’t do this. If someone who is usually happy is sad one day, you can detect it. Number two is imaginative transposition. You take what you think that person is experiencing and you put it on yourself, as if it were clothing. Third, you know at all times that that pain belongs to them, not you. You never create a transference response. If you have those three things, you have empathy—or at least the kind we can measure in the laboratory. We even know the neurons involved, what are called mirror-neurons. It’s very useful for teachers, or even as a CEO.
__ “When somebody’s feelings are intense, you do the Medina two-step. First, you have to verbally describe to the person what they see on the person’s face. You look pissed off. And then you make a guess: I bet you’re pissed off because you got this report late. If you do things like that, you can actually see people’s heart rates go down. They immediately sense that they might be understood. That alleviates stress in a relationship.”


“It wasn’t until about six or seven years ago that we had any idea why you needed sleep. It’s not energy-restorative—that’s another myth you can throw out. There’s only one point in the sleep cycle when you’re saving more energy than you’re expending.
__ “We now think we know why you sleep: memory consolidation. The rumor is, a graduate student made a mistake and turned it into a PhD. He was teaching a rat to go through a maze, and had 100 electrodes buried in the rat’s brain. As the rat was learning the maze, the researchers watched what was going on in the rat’s brain. They found a maze-specific signature. When the rat learned the maze, the rat deployed the maze-specific signature. The rumor is, the grad student forgot to remove the electrodes or turn off the equipment. So he gets up the next morning and sees the machines are still on. The rat is still asleep, and it learned the maze. When he looks at the printout, he sees the thing that made his PhD: the maze-specific pattern had been deployed all night long. The rat was replaying what he had learned that day a thousand times at night. All of a sudden it hit him: The rat is sleeping so he can turn off all the sensory input and just pay attention to the psychological interiors—what he needed to learn. So the student decided to see if he disrupted the rat’s sleep, if it would destroy the learning he did the previous day. And that’s exactly what he found.
__ “If you disrupt somebody’s sleep, you disrupt their offline possessing. So now we know why we sleep: So that we can learn.” bw


  1. Thank-you so much for this valuable information! As a teacher with a background in cognitive psychology, this is great, factual, usable information I can use right away, and everyday!

  2. What of the rich complexity of the Unconcious mind as Freud and Jung defined it? Is it really just meat and electricity up there?

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