Josh Kaufman

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Notes on Brain Rules by John Medina

If you don’t know how the human brain works, you’re at a major disadvantage when it comes to business: cognitive literacy can help you discover why you behave in certain ways, as well as help explain the behavior of others. John Medina’s Brain Rules is an entertaining and informative look at how our brains work – and how we can put that knowledge to practical use.

About John Medina

John Medina is the author of the Personal MBA-recommended book Brain Rules , as well as the upcoming book Brain Rules for Baby , which is about childhood neurological development. For more information about John Medina’s work, check out

Here are 10 big ideas from John Medina’s Brain Rules

1: Our brains are fundamentally physical systems that require proper nutrition, exercise, rest, and sleep to function optimally.

Your mind and your body aren’t separate things - your brain is a physical system that has physical needs. Similar to the primary ideas in The Power of Full Engagement , you can’t skimp on things like sleep, exercise, and rest if you want your mind to function at peak performance.

2: Everyone’s brain develops differently, based on their experiences and physical environment.

Your brain is malleable - a concept neuroscientists call “plasticity." The structure of your brain literally changes as your environment and experiences change - a process that continues as long as you live.

Since everyone experiences a slightly different environment and very different experiences over a lifetime, everyone ends up with a unique brain that processes information in a unique way. While there are many commonalities, there is no “standard" brain.

3: The brain is primarily a survival tool that pays particular attention to threats and opportunities by stimulating emotions and actions.

Our brains are designed to protect us. 10,000+ years ago, threats were everywhere in our environment - enemy tribes, predators, dangerous animals, and hostile elements. In order to survive long enough to reproduce, our ancient ancestors had to live long enough to take advantage of available opportunities.

Our modern Environment is very different than what our ancient ancestors experienced - opportunities are plentiful, and true life-threatening dangers are relatively scarce. This dynamic leads to what I call Caveman Syndrome - since we’re trying to run modern software on ancient hardware, our prehistoric brains constantly magnify perceived threats and overlook opportunities. That’s why humans often seem to do so many irrational and inefficient things.

4: Multitasking is a myth - your brain can only focus on one thing at a time.

Think of attention as the beam of a flashlight. No matter how hard you try, you can never shine the flashlight on two separated objects simultaneously - all you can do is rapidly switch the beam back and forth between them.

Our Attention works the same way. True multitasking, in the sense of paying attention to more than one task in parallel, is beyond the capability of the human mind. When you’re juggling tasks, all you’re really doing is switching the focus of your attention back and forth between the tasks you’re trying to keep track of.

Every time you switch, you lose productivity, since your brain has to take a moment to re-load information about what you’re trying to focus on. I call this the Cognitive Switching Penalty , and it’s a productivity killer.

For best results, focus on one (and only one) thing at a time. Multitasking may make you feel more productive, but it’s only a feeling - and that feeling is misleading.

5: Emotion, context, and repetition can help consolidate and store patterns as memories in our brain.

Our brains don’t work like computer disks, storing information in neat little organized files. Memories are patterns that are stored once they are recognized in the world at large. The key to remember is that memories are contextual - stored in a massive network of Associations and relationships, which your brain uses to recall patterns quickly.

Emotion and repetition help consolidate memories because they’re indicators of importance. Things that excite, frighten, depress, or anger you are stored more quickly because those emotions are very important ancestral survival cues. Repetition indicates that the pattern is common in the environment, which also is a clue that it’s important in some way.

If you’ve ever wondered why beer ads feature bikini-clad women and confident men, the 6:00pm news is frightening and depressing, or why people care what brand of golf clubs Tiger Woods prefers, remember that memory works via context and association.

6: Our brains mix long-term memories with new sensory data to mentally simulate potential actions before we actually act.

One of the reasons our brain is so useful is that it helps us predict the consequences of our actions. Mental Simulation allows us to imagine the results of our actions before we actually act, which keeps us out of trouble. Our brain is constantly in Pattern Matching mode, saving the results in memory.

When we’re trying to figure out what to do in any given situation, our brains rely on the patterns stored in memory to figure out what to do. Combined with the perceptions we’re taking in of our environment, memories help us quickly figure out what to do next when the best action to take is unknown or ambiguous.

6: Chronic stress and exhaustion can dramatically affect your brain’s ability to function and learn.

Our bodies and minds are built to handle stress, but not for very long. Remember the ancestral environment - threats were sudden and acute, but brief. (Either the tiger caught and ate you, or it got bored and went away after a few minutes.)

Now, stresses are much less acute, but can be chronic - you can be afraid of your boss firing you for decades, and we aren’t very well equipped to handle stress for that long. The hormones involved (adrenaline , cortisol , DHEA , etc) can wreak havoc on our bodies and minds if present in our systems every hour of every day.

When you’re stressed and tired for too long, your mind begins to function at a much lower capacity, impairing your ability to think and make decisions. We’ll talk about ways to avoid this cycle in The Path of Least Resistance , but for the moment, if you’re chronically stressed and tired, you need to change the structure of your environment to remove the primary stressors ASAP.

8: The best way to capture someone’s attention is to constantly provide a wide array of new input in as many sensory modalities as possible.

Our minds are drawn to pay attention to new stimuli. Look at media like TV, movies, video games, and the Internet - they’re constantly changing, providing new things to pay attention to every few seconds. That’s why it’s so easy to lose hours paying attention to them.

On the flip-side, have you ever tried to meditate or just sit in an empty room for a few minutes? In a few minutes (seconds?), you’ll inevitably begin to feel anxious, and your mind will start searching for something new to pay attention to.

If your job involves attracting and keeping Attention , don’t underestimate how much the human mind needs Novelty. At a minimum, when you’re in a live environment, introduce a new idea or stimulus every 10 minutes or less - that’s how Dr. Medina intentionally structures his coursework for maximum sustained student attention.

9: Gender differences are very real - male and female brains have important physical differences.

Regardless of political and ethical questions of gender equality, male and female brains are empirically different. The exact differences aren’t completely understood, but it’s a mistake to assume male and female brains work the same way.

Male brains, physiologically, have a larger amygdala (which plays a primary role in processing emotional reactions) and produce serotonin (a neurotransmitter involved in many behaviors, including social dominance and aggression) more quickly. As a result, males under stress tend to engage the right hemisphere amygdala and work to get a quick overall read on the situation to identify potential threat and next actions.

Female brains under stress engage the left amygdala, which is responsible for parsing the emotional details of perceptions vs. the gist. Female brains also tend to develop much more quickly when it comes to verbal and social skills, and on the whole, tracking and maintaining complex relationships between people comes much more naturally. In a sense, female brains process social cues in much higher resolution than male brains.

Since male and female brains are different, it pays to consciously benefit from both approaches by valuing and planning for them - one of the many compelling arguments for diversity in your team, which we also discussed in StrengthsFinder 2.0.

10: Our brains remain plastic throughout life - we’re constantly learning via exploration and experimentation.

The old model of human neurology was that, after childhood, your mental capacity and skills were fixed and incapable of change. New advances in neuroscience indicate that the brain continues to change and grow throughout life, which is good news for learning new tricks at any age.

If you’ve ever assumed you’re “too old" to master a new skill or try something different, that’s good news. Your brain will always maintain the capacity for change and growth, which means you’re capable of making progress toward any goal you set your mind to. The best way to learn new things is to explore and Experiment , so go out into the world and try something new!

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