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Most of us have no idea of how our brain works.

John Medina introduces us to 12 brain rules we know about how the brain works.

He does not only present them but also gives ideas on how to apply them in our daily lives.

The information provided is not voluminous, only the information needed for comprehension is provided.

Back to the jungle

What we know about the brain comes from biologists who study brain tissues, experimental psychologists who study behavior, cognitive neuroscientists who study how the first relates to the second, and evolutionary biologists.

Our evolutionary history tells us this:

The brain appears to be designed to:

  1. Solve problems
  2. related to surviving
  3. in a unstable outdoor environment
  4. and to do so in nearly constant motion.

John calls this the brain’s performance envelope.

Each subject in the book relates to this performance envelope.

Our brains actually were built to survive in jungles and grasslands.

12 Brain Rules


How and why did our brains evolve?

It all comes down to sex. Our bodies latched on to any genetic adaptation that helped us survive long enough to pass our genes on to the next generation.

And there are 4 concepts that explain how we came to conquer the world.

  1. Symbolic reasoning/Dual Representational Theory:

    Stated formally, it describes our ability to attribute characteristic and meanings to things that don’t actually possess them.

    We combine symbols to derive layers of meaning.

    With words, with language, we were able to extract a lot of knowledge about our life situation without always having to learn it the hard way.

  2. Adaptation:

    We gave up stability. We began not to care about consistency within a given habitat because consistency wasn’t an option.

    Those who haven’t been able to quickly solve new problems or learn from their mistakes haven’t survived long enough to pass on their genes.

    The net effect of this evolution was that rather than becoming stronger, we became smarter.

  3. Walking upright on two legs:

    Walking on two legs instead of four frees our hands and makes us consume less energy.

    Our ancestral bodies used the excess energy not to inflate their muscles but to inflate their minds.

    This led to the masterpiece of evolution, called the prefrontal cortex.

    The prefrontal cortex governs several uniquely human cognitive talents, called “executive functions”: solving problems, maintaining attention, and inhibiting emotional impulses.

  4. 3 brains in 1:

    Lizard brain controls: breathing, heart rate, sleeping, waking.
    Mammalian brain involve: fighting, feeding, fleeing, and reproductive behavior
    Cortex: each region of the cortex is highly specialized, with sections for speech, for vision, for memory

Finally, we learned to cooperate, which comes with understanding others.

We create a view, however brief of what people think.

Making inferences are the signature characteristic of something called the Theory of Mind.

This ability to peer inside somebody’s mental life and make predictions takes a tremendous amount of intelligence.

Many researchers believe that there is a direct line between predicting what other people think and manipulating other people within a group and our intellectual domination of the planet.

On the right of the image, we can see the cover of the book, and on the left you can see the word summary.


Our evolutionary history tells us that we were moving.

We moved to look for trees to scamper up and dine on.

Anthropologist, Richard Wrangham, says that males may have walked and run 10 to 20 Km a day and a half for females.

That means our fancy brains developed not while we were lounging around but while we were exercising.

Data tells us the human brain became the most powerful in the world under conditions where motion was a constant presence.

Having an active life has a lot of benefits.

Researchers have found that one of the greatest predictors of successful aging is the presence or absence of a sedentary lifestyle.

Not only that, exercising also has an impact on mental alertness too.

A lifetime of exercise results in a sometimes astonishing elevation in cognitive performance, compared with those who are sedentary.

Exercisers outperform couch potatoes in tests that measure long-term memory, reasoning, attention, and problem-solving skill.

It can be done with aerobic exercise, 30 minutes at a clip, two or three times a week.


Sleep loss hurts attention, executive function, working memory, mood, quantitative skills, logical reasoning ability, general math knowledge.

Eventually, sleep loss affects manual dexterity, including fine motor control, and even gross motor movements, such as the ability to walk on a treadmill.

And the lack of sleep doesn’t have to be huge to hurt you!

Just getting less than seven hours of sleep a night is enough to decrease your performance.

A study on soldiers responsible for operating complex military hardware reveals unbelievable results.

Only one night’s loss of sleep resulted in about a 30 percent loss in overall cognitive skill, with a subsequent drop in performance.

Bump that to two nights of sleep loss, and the loss in cognitive skill doubles to 60 percent.

Now that we know the consequences of sleep loss let’s go over how we can improve our sleep.

One thing to know is that we vary in how much sleep we need and when we prefer to get it. And this also changes as we age.

There are 3 types:

  1. Lark:

    About one in 10 of us are most alert around noon and feel most productive at work a few hours before they eat lunch.

    They don’t need an alarm clock, because they invariably get up before the alarm rings, often before 6:00 a.m.

  2. Owl:

    Also, at one in 10, are people who are most alert around 6:00 p.m., experiencing their most productive work times in the late evening. 

    They rarely want to go to bed before 3:00 a.m.

    Owls invariably need an alarm clock to get them up in the morning, with extreme owls requiring multiple alarms to ensure arousal.

  3. Hummingbird:

    Larks and owls cover only about 20 percent of the population.

    The rest of us are called hummingbirds.

    True to the idea of a continum, some hummingbirds are more owlish, some are more larkish, and some are in between.

However, there is something experienced by nearly everyone on the planet.

It goes by many names – the midday yawn, the post-lunch dip, the afternoon “sleepies.”

We’ll call it the nap zone, a period of time in the midafternoon when we experience transient sleepiness.

Some think that a long sleep at night and a short midday nap represent default human sleep behavior, that it is part of our evolutionary history.


Gifted researchers Jeansok Kim and David Diamond came up with a three-part definition of stress.

According to them, if all three are happening simultaneously, a person is stressed.

  1. Measurable physiological response:

    There must be an aroused physiological response to stress, and it must be measurable by an outside party.

  2. Desire to avoid the situation:

    The stressor must be perceived as aversive, something that, given the choice, you’d rather not experience.

  3. Loss of control:

    The person must not feel in control of the stressor.

This element of control and its closely related twin, predictability, lies at the heart of learned helplessness.

Learned helplessness can be described as both the perception of inescapability and its associated cognitive collapse.

As evolution tells us, our stress responses were shaped to solve problems that lasted not for years, but for seconds.

The saber-toothed tiger either ate us or we ran away from it.

These days, our stresses are measured not in moments, but in hours, days, and sometimes months with hectic workplaces, screaming toddlers, and money problems.

Our system isn’t built for that.

Chronic stress affects memory formation, executive functions, creativity, motivation, productivity, and even the immune system.

Not surprisingly, people who experience chronic stress are sick more often.


When you learn something, the wiring in your brain changes.

The brain acts like a muscle.

The more activity you do, the larger and more complex it can become.

Whether that equates to more intelligence is another issue, but one fact is indisputable: What you do in life physically changes what your brain looks like.

Some of the neural connections you’re born with have preset functions: they control basic housekeeping functions like breathing, heartbeat, etc…

Researchers call this “experience independent” wiring.

There is also “experience expectant” wiring related to areas such as visual acuity and perhaps language acquisition.

And finally, we have “experience dependant” wiring. We are hardwired to be flexible.

Our brains are so sensitive to external inputs that their physical wiring depends upon the culture in which they find themselves.

Since we are not all wired the same way we should customize classrooms and workplaces.


The more attention the brain pays to a given stimulus, the more elaborately the information will be encoded, that is, learned and retained.

Michael Posner came up with a theory of how the brain pays attention.

According to him, we pay attention to things using three separable but fully integrated networks of neural circuitry in the brain.

The brain’s first system is called the Alerting or Arousal Network.

It monitors the sensory environment for any unusual activities.

The second network is called the Orienting Network.

It is activated when we orient ourselves to an attending stimulus.

The third system, the Executive Network, controls what action we take next.

So we have the ability to detect a new stimulus, the ability to turn toward it, and the ability to decide what to do based on its nature.

With his findings, we have arrived to conclude that we can’t multitask.

The brain naturally focuses on concepts sequentially, one at a time.

A person who is interrupted takes 50 percent longer to accomplish a task and makes up to 50 percent more errors.

On the bottom of the image, we can see the cover of the book, and on the top can see the word summary.


The brain has different types of memory systems, many operating in a semiautonomous fashion, and the one we know the most about is declarative memory.

Declarative memory involves something you can declare, such as “The sky is blue.” Or when you need to remember your Social security number.

It involves four steps: encoding, storing, retrieving, and forgetting.

German researcher Herman Ebbinghaus showed that memories have different life spans.

Some memories hang around for only a few minutes, then vanish. Others persist for days or months, even for a lifetime.

He uncovered one of the most depressing facts in all of education: People usually forget 90 percent of what they learn in a class within 30 days. And the majority of this forgetting occurs within the first few hours after class.

Ebbinghaus also showed that one could increase the life span of memory by repeating the information in time intervals.

Steps to store information

  • Enconding:

    The quality of encoding stage-those earliest moments of learning-is one of the single greatest predictors of later learning success.

    It is a common impression that the brain is a lot like a recording device: that learning is something akin to pushing the “record” button, and remembering is simply pushing “play.”


    The initial moment of learning – of enconding – is incredibly mysterious and complex. The little we do know suggests information is chopped into discrete pieces and splattered all over the insides of our mind.

    To encode information means to convert data into, well, a code. Information is translated from one form into another so that it can be transmitted.

    From a physiological perspective, the brain must translate external sources of energy (sights, sounds, etc.) into electrical patterns the brain can understand.

    The brain then stores these patterns in separate areas.

    From a psychological perspective, it can be viewed as the manner in which we apprehend, pay attention to, and organize information so the we can store it.

    The ease which we remember something depends in part on process used for encoding.

    All encoding processes share certain characteristics. If we heed two of them we can better encode (and thus remember) information.

    1. The more elaborately we encode information at the moment of learning, the stronger the memory.

    When initial encoding is more detailed, more multifaceted, and more imbued with emotion, we form a more robust memory.

    2. The more closely we replicate the conditions at the moment of learning, the easier the remembering.

    Moreover, remembering is easier if you understand what the information means and if when you are teached real-world examples are used.

  • Storing:

    The same neural pathways that the brain recruits to process new information are the same neural pathways that the brain use to store information.

    This is why the initial moments of learning are so critical to retrieving what has already been learned.

    After the first few moment of encoding declarative information goes into the short-term memory.

    Short-term memory is a collection of temporary memory capacities-busy work spaces where the brain processes newly acquired information.

    Each work space specialized in processing a specific type of information: auditory information, visual information, stories, plus a “central executive” to keep track of the activities of the others.

    These all operate in parallel. To reflect this multifaceted talent, short-term memory is now called working memory.

    Working memory is the bridge between the first few seconds of encoding and the process of storing a memory for a longer time.

    If the information held in working memory is not transformed into more durable form, it will soon disappear.

    The process of converting short-term memory traces to longer-term forms is called consolidation.

  • Retrieving:

    In the short-term phase, the memory trace is flexible, labile, subject to modification, and at great risk of extinction.

    There is growing evidence that when previously consolidated memories are recalled from long-term storage to consciousness, they revert to short-term memory stage.

    Acting as if they were newly etched into working memory, these memories may need to be reprocessed in order for them to stay in a lasting form.

    This process is formally termed reconsolidation.

    Researchers think there is two ways we retrieve information.

    One model passively imagines libraries. The other aggressively imagines crime scenes.

    In the library model, memories are stored in our heads the same way books are stored in a library. Retrieval begin with a command to browse through stacks and select a specific volume.

    Once selected, the contents of the volume are brought into conscious awareness and read like a book.

    The memory is retrieved. This is the model we use soon after learning something (within minutes, hours, or days).

    But as time goes by, and once-clear details fade, we switch to second model. 

    This model imagines our memories to be more like a large collection of crime scenes.

    There is a crime scene full of fragments of data. You have to examine the partial evidence available, and make a reconstruction of what was actually stored.

    The brain, however isn’t afraid to use a little imagination.

    In a desire to create organization out of a bewildering and confusing world, the brain fills the gaps with fragments, inferences, guesswork, and often-distrubingly-memories not even related to the actual event.

    In order to create reliable long-term memories you have to repeat to remember.

    Memory may not be fixed at the moment of learning, but repetition, doled out in specifically timed intervals, is the fixative.

    The typical human brain can hold about seven pieces of new information for less than 30 seconds! If something does not happen in that short stretch of time, the information becomes lost.

    If you want to extend the 30 seconds to, say, few minutes, or even an hour or two, you will need to consistently reexpose yourself to the information.

    This type of repetition is sometimes called maintenance rehearsal.

    It is good for keeping things in working memory, that is, for a short period of time. But there is a better way to push information into long-term memory.

    It’s called elaborative rehearsal, and it’s the type of repetition most effective for the most robust retrieval.

    A great deal of research shows that thinking or talking about an even immediately after it has occurred enhances memory for that event, even when accounting for differences in type of memory.

    The timing of the repetitions is a key component.

    Although scientists are not yet sure which time intervals supply all the magic.

    But taken together, the relationship between repetition and memory is clear.

  • Forgetting:

    Forgetting plays a vital role in our ability to function for deceptively simple reason.

    It allows us to prioritize.

    Anything irrelevant to our survival will take up wasteful cognitive space if we assign it the same priority as events critical to our survival. So we don’t.

    At least, most of us don’t.

    It allow us to drop pieces of information in favor of others.

Sensory Integration

Data suggests that things are perceived by the coordination of our senses.

Imagine the sound of a single gunshot over a green field during a war.

From the beginning, your senses consult and influence each other.

As the ears and eyes simultaneously pick up gunshot and smoke, the two impressions immediately confer with each other.

They perceive that the events are occurring in tandem.

The picture of a rifle firing over an open field emerges in the observer’s brain.

Perception is not where the integration begins but where the integration culminates.

The world is multisensory and has been for a very long time.

Knowing that the brain cut its developmental teeth in an overwhelmingly multisensory environment, you might hypothesize that its learning abilities are increasingly optimized the more multisensory the situation is.

You might further hypothesize that the opposite is true: Learning is less effective in a unisensory situation.

That is exactly what you find.

Every sensory system must send a signal to the thalamus asking permission to connect to the higher levels of the brain where perception occurs. except for the smell.

Smell has the unique advantage of being able to boost learning directly, without being paired with another sense.

However, this is true for only certain types of memory, like emotional memory.

Odors are not so good at retrieving declarative memory.

Smell aside, there is no question that multiple cues, dished up via different senses, enhance learning.

They speed up responses, increase accuracy, improve stimulation detection, and enrich encoding at the moment of learning.


Studies point to the direction that visual processing doesn’t just assist in the perception of our world. It dominates the perception of our world.

The brain visual system actively deconstructs information given to it by the eyes, pushes it through a series of filters, and then reconstructs what it thinks it sees.

Or what it thinks you should see.

If you think the brain has to devote to vision a lot of its precious thinking resources, you are right. Visual processing takes up about half of everything your brain does, in fact.

This explains why vision affects other senses.

The more visual the input becomes, the more likely it is to be recognized and recalled.

It’s called the pictorial superiority effect.

Tests performed years ago showed that people could remember more than 2,500 pictures with a least 90 percent accuracy several days later, even though the subject saw each picture for about 10 seconds.

Accuracy rates a year later still hovered around 63 percent.

Pictures demolish text or oral presentations.

They are not just less efficient than pictures for retaining certain types of information; they are far less efficient.

If information is presented orally, people remember about 10 percent, tested 72 hours after exposure.

That figure goes up to 65 percent if you add a picture.

With, text no matter how experienced a reader you become, your brain will still have to stop and ponder the individual features of each letter in order to process it.

By now, you can probably guess why this might be.

Our evolutionary history was never dominated by books or email or text messages.

It was dominated by trees and saber-toothed tigers.

The things in a picture that grab our attention and transfer information are color, orientation. size and motion.


We think we have an understanding of at least some of the effects of music on cognition.

The reason why is because the matter is unsettled on why music exists, and scientists don’t agree on how to even define music.

Still, researchers forge ahead with studies on cognition and social skills.

They’ve discovered fascinating ways that music may benefit the brain.

Before going over the benefits, it’s important to understand that there is a difference between what you gain from listening to music and music training.

Music training improves spatiotemporal reasoning, detecting alteration in sound, boots language skills, improves social skills, and detecting emotions.

Much research remains to be done, however. It’s unclear whether music training is the direct cause of those improvements, or whether people who are naturally better fine-grained discrimination have a tendency to like music and stick with music lessons.

On the other hand, listening to music changes your mood. It can make people happy, calms them down, maybe even make them feel close to each other.

Music therapy also helps mentally ill patients.

Unfortunately, too many of the studies don’t prove the cause, and they’re all done in a lab setting.


Men’s and women’s brains are different.

It all starts with genes, which determine whether we become male or female.

As you might know, there is four hundred million sperm that fall all over themselves attempting to find one egg during intercourse.

Creating a human takes 46 chromosomes.

Twenty-three come from Mom, and 23 come from Dad.

Two are sex chromosomes, either X or Y.

At least one of your sex chromosomes has to be an X chromosome, or you will die.

If you get two X chromosomes, you become a woman, an X, and Y makes you a man.

The Y can be donated only by sperm – the egg never carries one – so sex assignment is controlled by the man.

There is terrible inequality between the two chromosomes.

The X chromosome carries about 1,500 genes, which do most of the heavy lifting to develop an embryo.

The little Y chromosome carries 100 genes.

With only a single X chromosome, males need every one of those 1,500 genes. With two X chromosomes, females have double the necessary amount.

The female embryo uses what may be the most time-honored weapon in the battle of the sexes to solve the problem of two Xs: She simply ignores one of them.

This chromosomal silent treatment is known as X inactivation.

Because males require all 1,500 X genes to survive, and they have only one X chromosome, X inactivation does not occur in guys.

And because males must get heir X from Mom, all men are literally, with respect to their X chromosome, unisexed.

Cells in the female embryo are a complex mosaic of both active and inactive mom-and-pop X genes, there are no preferences.

These bombshells describe our first truly genetic-based findings of potential differences between men’s and women’s brains.

What do many of the X’s 1,500 genes do?

Collections of these cells create large brain structures, like the cortex, the hippocampus, the thalamus, and the amygdala.

The frontal and prefrontal cortex control much of our decision-making ability, it has been found that certain parts of this cortex are fatter in women than in men.

The limbic system, home to the amygdala, controls not only the generation of emotions but also the ability to remember them.

This region is much larger in men than it is in women.

At rest, female amygdalas tend to talk mostly to the left hemisphere, while male amygdalas do most of their chatting with the right hemisphere.

The right side of the brain tends to remember the gist of an experience, and the left brain tends to remember the details.

In stress situations, men handle it by firing up the amygdala in their brain’s right hemisphere while women experience it with the opposite hemisphere.

Findings suggest that women recall more emotional autobiographical events, more rapidly and with greater intensity than men do.

Women communicate verbally better than men.

They also tend to use both hemispheres when speaking and processing verbal information. Men primarily use one.

In addition, ladies tend to have a thick cable connecting their two hemispheres. The men’s is thinner.

Girls seem to be verbally more sophisticated than little boys as they go through the school system.

They are better at verbal memory tasks, verbal fluency tasks, and speed of articulation.

These findings make the strongest argument for the genders to work together.

Since it is clear that we need the gists as much as the details.

We certainly did so for the several million years it took to establish these differences and with them together we conquered the world.


We evolved as explorers.

Problem-solving was greatly favored in the unstable environment we were in.

When we came down from the trees to the savannah, we did no say to ourselves, “Good Lord, give me a book and lecture and a board of directors so that I can spend 10 years learning how to survive in this place.”

Our survival did not depend upon exposure to organized, preplanned packets of information.

It depended upon chaotic, reactive information-gathering experiences.

That’s why one of our best attributes is the ability to learn through a series of increasingly self-corrected ideas.

The good news is that research shows that the brain is wired to keep learning as we age.

Some regions of the adult brain stay as malleable as a baby’s brain, so we can grow new connections, strengthen existing connections, and even create new neurons. allowing all of us to be lifelong learners.

We didn’t always think that.

Although, we do lose synaptic connections with age.

Some estimates of neural loss alone are close to 30,000 neurons per day.

But the adult brain also continues creating neurons within the regions normally involved in learning.

These new neurons show the same plasticity as those of newborns.

Through life, your brain retains the ability to change its structure and function in response to your experiences.

I think that we must do a better job of encouraging lifelong curiosity, in our workplaces, our homes, and especially in our schools.

For me, curiosity is the greatest Brain Rule of all but unfortunately, I cannot prove it.

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