brain rules

Brain Rules John Medina

A scientist named John Medina, who specializes in studying the brain, guides us through the latest discoveries about how our brains work. He does this to help us live better lives and understand ourselves more. John Medina is a respected neuroscientist and teaches at the University of Washington.

Brain Rules summary

In Brain Rules, John Medina highlights the importance of connecting three areas: brain science, education, and business. Collaboration between these fields leads to valuable resources. He also mentions that not reading scientific journals can limit your understanding of how the brain functions. His book presents 12 principles as rules for personal growth and improvement.

brain rules cover book

Rule No. 1 Physical exercise boosts brain power

To grab and keep our attention, as developed in Brain Rules, John Medina practices the strategies he teaches. He begins by telling the story of an impressive 70-year-old man, Jack LaLanne, known as a fitness pioneer. He reveals the key to this older man’s vitality.

Here’s something interesting:

While there are different opinions on human history, experts in the study of early humans agree on one thing: humans were on the move. John Medina shares some scientific facts (theory No. 3) that challenge our traditional understanding of how humans migrated through the Bering Strait.

I’ll wrap up this aside with information from research in Quebec, particularly from Patrick Couture’s website:

“New archaeological discoveries challenge this paradigm. Here are some of the most plausible theories.”

Possible Origins of the First Americans – Patrick Couture

Who is right?

“In my humble opinion, it’s a mistake to limit oneself to one of these four theories. Each of them seems plausible, and why couldn’t they all be plausible?”

Let’s talk about theory No. 3 that John M. discusses on page 17. According to this theory, our ancestors, the Homo sapiens, left Africa about 100,000 years ago and arrived in South America, specifically Argentina, 12,000 years ago. They faced many challenges like crossing water bodies, mountains, jungles, and deserts. What’s even more incredible is that they did all of this with basic tools and techniques since they didn’t have things like wheels or metal.

Now, let’s think about this: Cognitive abilities improved because of physical activity. So, does physical activity still affect how smart we are today? John M. takes us on an amazing journey to find out with a story about two 90-year-old men. One is Jim, a lonely resident in an American retirement home, and the other is Frank, a famous architect. This story helps him understand how exercise benefits the brain.

Is there a factor that can predict how well you will age?

Can exercise change people, considering how unique humans are? Well, researchers discovered that exercise can reduce the risk of heart disease by 50%, the risk of memory problems by 50%, and the risk of Alzheimer’s disease by 60%. The person responsible for this breakthrough isn’t a scientist but a fitness trainer named Steven Blair (p. 24). These benefits apply to both women and men, especially in severe cases and among older adults. But what about children?

Surprisingly, there have been few studies on this topic, even though there’s a clear need, especially among schoolchildren. The author shares some of these studies with us, including the case of Dr. Antronette Yancey, a former model turned scientist who practices the Art of Performance.

brain rules survival

Rule No. 2: Survival: To survive, the brain itself has also evolved

In the second chapter, the author starts by realizing something with the help of his 4-year-old son, Noah. In just two seconds, Noah turns a stick into a sword, showing his father how humans have developed a special skill over the years: symbolic reasoning.

One of the parodies of human evolution on

When humans look at something like a stick or a piece of wood (or any symbol), they don’t always see it as just that. For some, it can be a sword, a spear, a fishing rod, and more. Thanks to words and language, humans have been able to gain a lot of knowledge. It’s like this book; you can learn from it without experiencing everything yourself. This is the power of imagination and symbolic reasoning, something unique to humans.

This is what scientist Judy Deloache calls the “Dual Representational Theory,” and it’s the key difference that sets us apart from gorillas and other animals closely related to humans.

It’s the combination of different symbols that gives humans language skills, the ability to write in languages, do math, create art, and more. For example, combining points and scribbles can become music or poetry, and combining circles and squares leads to geometry.

The author then explains how our brain evolved rapidly due to the need to adapt to significant changes in climate over 40 million years, including 17 ice ages. This forced our ancestors to travel through various terrains, including forests and areas with many predators. They had to adapt to new situations where danger was everywhere.

According to paleoanthropologist Richard Potts, humans didn’t resist change; instead, they gave up stability and learned to adapt to change itself.

This theory simplifies how humans learn. Our brain stores a wealth of knowledge, and we can use that knowledge to improvise, like a jazz musician with an instrument. Our knowledge base helps us recognize our mistakes, and our ability to improvise allows us to gain new knowledge and lessons.

What was the role of learning bipedalism in our brain evolution?

J.M. explains that our ancestors used to travel 20 kilometers per day on all fours, which required a lot of energy. However, walking on two legs saved them energy, which they could then use to fuel their brains (even though the brain only makes up 2% of body weight, it consumes 20% of our energy).

The idea of learning and teaching in adults came about because of the need for survival and protecting their offspring. Humans, compared to some other animals, were physically disadvantaged, so they had to strategize to deal with dangers. Teamwork became the solution.

Learning to cooperate means understanding others in terms of their needs, strengths, and weaknesses.

Even though John Medina is a neurologist, he’s also a great teacher. He uses an example to show how humans learned to work together effectively. He quotes the sentence: “The husband died, then the woman died.” If you add two words to that sentence, “The husband died, then the woman died of grief,” you can see how emotions and our ability to learn are closely connected.

This has consequences for success in two contexts:

  • Education: The relationship between the learner and the teacher.
  • Business: The relationship between the employee and the boss.

brain rules john medina

Rule No.3 Brain wiring: Each person’s brain is wired in a unique way

In the next part of the book, the author brings the stories together again to help us stay interested and better understand the topic.

Areas of different brain activities

Different parts of the brain develop differently in individuals based on their experiences and environments. John M. uses the example of twins who, despite having identical experiences, don’t develop the same mental structures.

To help us understand what happens in the brain when we learn, the author takes us on a journey inside the human body, similar to the one in the 1966 film “Fantastic Voyage.”

In school, you learn that living things are made up of cells, but the author tells us that the outer layer of our skin, about 4kg worth, is actually made up of dead cells. It acts as a protective shield for the living cells beneath.

Voyage through the infinitely small

To help us understand what a nerve cell is, John uses the example of a crushed fried egg, which looks like a multi-pointed star. He takes us into the tiny world of nerve cells, comparing it to underwater forests and canyons between neurons.

John explains that a child up to the age of 3 has the same number of connections between nerve cells as an adult. This challenges the belief that early brain development determines an adult’s intelligence. However, between ages 3 and 8, a pruning process occurs, eliminating some connections. This process starts again during puberty and continues until around age 20 when the brain reaches its adult form.

The author emphasizes that brain development is not a precise, military-like process and gives the example of how some teenagers mature earlier than others.

A significant finding is that 10% of primary and secondary school students may not have the correct neural connections for reading, which challenges the educational system’s reliance on age-based learning.

To conclude this chapter and the third brain rule, the author suggests ideas for collaboration between scientists, educators, and businesses. He discusses the concept of measuring empathy and applying personalized approaches to each student or employee.

Rule No. 4 Attention: We tend to ignore things that are boring.

In this chapter of Brain Rules, John Medina shares an experience from around 3 o’clock in the morning when he suddenly wakes up to see an unfamiliar silhouette in his house. He felt fear and confusion but had to take action. Even though this situation lasted only a few seconds, it left a lasting impression in his mind.

The chapter highlights the importance of attention in learning. The author explains that our brains can stay focused for about 10 minutes, and in classrooms or work environments, people often start losing focus after about 15 minutes.

The challenge in both education and business is to find ways to keep people engaged and attentive for longer periods.


What grabs our attention is influenced by a sense of déjà vu. This means our brain connects new information with what we already know from past experiences. It’s like a part of our brain always keeps an eye on our surroundings, looking for familiar things.


Culture also plays a big role in what we pay attention to, even in similar situations. John M. compares two groups: Asians and Americans.

When an Asian person looks at a visual scene, they see how objects in the foreground and background relate to each other. On the other hand, an American person often focuses mainly on the foreground and doesn’t pay as much attention to the context.

These cultural differences are important to consider when you’re presenting something, whether you’re a businessperson, teacher, or speaker. Your audience’s attention depends on how well you understand their interests.

But there are also many similarities, like external sensory stimulation, which grabs everyone’s attention. The author mentions the impact of good advertisements and the research of British neurologist Dr. Oliver Sacks, who showed that each side of our brain is like a projector for visual information.

In any situation, it’s essential to improve your ability to visualize, remember, and set the stage, as if you’re telling a story.

Emotions capture attention

Emotions act like sticky notes in our brain, making information more vivid, specific, and energetic. This is something everyone desires, including parents, teachers, and advertisers.

brain rules book

The meaning before the details

Advertising is a clear example of how emotions have a stronger impact than details. What do people remember over time? The feeling they get from an advertisement sticks with them more than the specific details.

There’s a fascinating experiment involving a neuroscientist, K. Anders Ericsson, and a waiter named Marc who remembers every item on a menu with over 500 choices. His secret is linked to a well-known principle among neuroscientists—the exceptional organization of data through associations of concepts. This principle can improve memory by 40%.

The myth that the brain can multitask

In this section, the author talks about attention, which is the resource we use to listen and stay engaged in a lesson or a boring speech from our boss. There’s scientific proof that we can’t focus on multiple tasks at the same time.

Think about the daily life of your children, students, colleagues, or employees who work on a computer with many programs open and listen to music while keeping their phones nearby. John M. explains what happens in your brain when you switch between tasks. Trying to multitask is like putting your left shoe on your right foot.

Research has shown that even reaching for something while driving can increase the risk of an accident by 9 times (like reaching for your cell phone).

The crucial point of this fourth rule is that the brain needs breaks to process information. Our education systems often force-feed information without giving the brain time to connect different sets of information.

John Medina’s 10-minute rule

This rule is for teachers, speakers, and business leaders alike. The author recommends using captivating stories with emotional hooks to engage their audience.

Rule No. 5: Short-term memory involves repeating information to remember it

Kim Peek, born in 1951 with a unique brain condition, couldn’t walk until he was 4 and had a damaged cerebellum. However, he possessed an extraordinary gift – the ability to read two pages at once, one with each eye, and remember everything forever. His brain became one of the two most studied brains in the 20th century, contributing to our current understanding of the subject.

The famous movie “Rain Man” was inspired by his incredible story.

This remarkable ability happens in the initial moments when his brain is exposed to information, similar to the early stages of learning in an ordinary brain.

Difference between memorizing and remembering

We still have a lot to learn about the brain’s various memory systems. One of the most well-known is declarative memory (like remembering that the sky is blue). It goes through four stages in its life cycle: encoding, storing (or retaining), retrieving, and eventually forgetting.

The second extraordinary case involves Hermann Ebbinghaus, born in 1850, who was studied for over 40 years by Brenda Milner, a psychologist from Montreal. However, she studied him not for his abilities but for his remarkable disabilities. After a bicycle accident and subsequent surgery, Ebbinghaus could no longer convert short-term memories into long-term ones. He couldn’t create new memories.

As a result of various discoveries, researchers have identified two types of memory. One is declarative memory, where we consciously build and announce memories (like recalling lists of words or numbers). The other is automatic processing, where we unconsciously acquire skills, like riding a bike.

brain processing

Different types of information processing

Scientists are still trying to figure out how the brain connects pieces of information.

It all begins when the brain encounters new information for the first time.

Encoding, the moment your brain starts to learn

Let me tell you about Tom, a young autistic boy observed by neurologist Oliver Sacks. Tom had an incredible talent: he could listen to complex music pieces and then play them on the piano from memory after hearing them just once. What’s even more astonishing is that he never had any formal music lessons. He could play different pieces with each hand while singing a third song, and he could even play with his back turned to the piano.

Contrary to what some may believe, we don’t have buttons to record and play information at will. The initial moment of learning, known as encoding, remains a mystery.

The author likens the encoding process to a blender in action without a lid, where information is broken into small pieces and projected onto the inside of our minds. To help us understand this better, John M. offers simple tests and exercises on page 119.

He then brings the discussion back to the practical and everyday aspects, highlighting three vital characteristics of the encoding process that are applicable in the worlds of business and education:

  • The better your information is encoded during the learning phase, the better you’ll remember it.
  • Information storage in the brain involves repeating the same mental circuit.
  • To improve memory retention, recreate the conditions present during the initial encoding, including the atmosphere and stimulated senses.

Rule No. 6: Long-term memory (Remember to repeat)

Imagine a small platform near a large bookstore surrounded by a slight fog. There are boats regularly docking and dock workers trying to unload stacks of books onto this platform. They barely have enough time to transport a few books to the bookstore before another boat arrives. They keep unloading new stacks while leaving the old ones behind.

Now, in the sixth chapter, the author uses this metaphor to describe memory, but it’s an outdated view. Short-term memory is much more active and complex than this.

The story of the first chess star, Miguel Najdorf, illustrates what’s called working memory, which is like a temporary space for processing information.

Today, scientists, like Alan Baddeley from Britain, have presented a model with three components: an auditory part (phonological loop), a visual part (visuospatial sketchpad), and an executive part (central executive), as explained by John Medina.

At the beginning, any piece of information you want to remember is like taking the first steps in a field with tall grass. If you don’t create pathways behind you, the information is at risk of disappearing.

Memory consolidation

Imagine the author sitting in front of the TV with his 6-year-old son, watching a dog show program. Suddenly, a childhood memory pops up out of nowhere. This memory reappears in the working memory, where it becomes flexible and has to go through a process called reconsolidation to be comfortably stored again.

In the previous chapter, we learned that working memory (the short-term one) comes in different forms. Now, scientists believe there are also various forms of long-term memory, although they don’t entirely agree on the details.

Some researchers talk about semantic memory (remembering facts and general knowledge), while others believe in the existence of episodic and autobiographical memory (recalling episodes from our lives where we’re the main character). You’ll discover more about these concepts.

For a long time, scientists thought that repeating or consolidating a memory didn’t reveal its original fragility. However, we now know that this belief is false. This highlights the importance that John Medina places on repetition. The awareness of an event and its storage in our memory are not permanent—they can change over time.

Retrieving (or retrieval)

Researchers have grouped memory processes into two main models: the library and the detective, like Sherlock Holmes. These models are useful depending on the type of information you want to find and how much time has passed since you learned it.

The brain hates emptiness

The library model is used in the early moments of our learning. It’s fresh, and memory details are still accurate. But as time goes by, our biological computer has to use the second model, like a detective, to fill in the gaps.

The brain always seeks to create a coherent story, and it doesn’t distinguish between real memory details and those that are unrelated or made up. John Medina confirms that the brain enjoys adding false information to complete its missing parts.

That’s why repetition is so important right after learning (along with meaning and emotions) and at regular intervals. This repetition is the closest thing to the original memory and helps fix it in place (the first learning rule specified by Jean-François Le Ny).

Wanting to discuss what you’ve learned or experienced right after it happens indicates the beginning of an emotionally engaging environment that enhances memory retrieval. This is an ideal goal in teaching, public speaking, or business regulations!

brain rules book summary

Long neurological chatter

In Brain Rules, John Medina uses an analogy of an overnight army (representing the cortex) and an old soldier’s experiment (representing the hippocampus) to explain how lasting memories are made. Despite 30 years of research, we still don’t fully understand how this process works. However, scientists have some knowledge about how these parts of the brain communicate, and the author simplifies this concept with imagination and teaching.

To illustrate, he mentions the 1968 film “Planet of the Apes,” where an astronaut crashes on a planet ruled by apes, only to realize with sadness that it’s actually Earth. His emotional reaction upon seeing a piece of the Statue of Liberty sticking out of the sand is spontaneous and linked to his memories of the past.

John makes a comparison here about how memories of Earth have changed over time, but it’s based on personal data and may not align with the astronaut’s experiences. The exchanges between his hippocampus and cortex relied on incomplete information to come to a supposed apocalyptic conclusion.


This is the story of Solomon Shereshevskii, a Russian journalist with an extraordinary ability to memorize lists of numbers and letters, even with more than 70 elements, both forwards and backwards. However, this ability had a significant drawback: he couldn’t forget, and he struggled to understand the meaning of what he was reading or the broader context of experiments.

Forgetting serves several important functions. It helps us prioritize events and acts as a safety valve for normal functioning. Additionally, forgetting can lead to the generation of new ideas. When you can’t recall a word or mix up names, it creates space in your memory for other information, allowing the formation of new connections. Highlighted in Brain Rules, John Medina explains that forgetting has been crucial in our evolution and helped us conquer our planet.

So, how can we practically apply this knowledge about long-term memory in education and business? John Medina offers ideas at the conclusion of this chapter.

Rule No. 7: Sleep…sleep well to think well

In 1965, a 17-year-old named Randy Gardner set a world record for staying awake. After just five days of being awake for a total of 11 days, he started experiencing problems similar to those seen in Alzheimer’s disease.

The scientist William Dement, often called the godfather of sleep research, had the opportunity to study Randy’s brain during this period. Remarkably, on the eleventh day, Randy was still able to beat William D. at pinball, 100 times in a row!

John Medina delves into this story and honestly admits that, despite spending about one-third of our lives asleep, we still don’t fully understand why we need sleep. Nevertheless, scientists have a pretty good idea, thanks to stories like this one.

Let me sleep on it

Around ten years ago, a laboratory rat fell asleep while in the middle of a maze experiment, still hooked up to electrodes. This unique situation allowed scientists to discover that even during sleep, the rat’s brain remained highly active.

What gets really interesting is when an unkind researcher woke the rat from its slumber. They found that the rat had trouble remembering the maze’s layout the next day. This led to the conclusion that sleep helps consolidate learning from the previous day, but this process depends on an uninterrupted slow-wave cycle.

You might wonder if this applies to humans too. John Medina explains that researchers have found similar mechanisms in humans, albeit in a more complex process. Human sleep involves emotional aspects and another phase known as REM (rapid eye movement) sleep, which is when most dreams occur. This phenomenon isn’t unique to humans but is observed in most placental mammals and birds as well.

So, what’s happening inside our brains during sleep? John takes us into a metaphorical battlefield where two forces clash. On one side, there are neurons and hormones, including chemicals like process C, which keeps you awake (usually for up to 16 consecutive hours). On the opposing side, there’s a similar process called process S, responsible for making you sleep. Typically, it can keep you asleep for about 8 hours, as is the case for most of us. John supports these findings with concrete examples.

The case of the nap, a period of beneficent sleep

The story of Lyndon Baines Johnson, the 36th President of the United States, is quite surprising. He had a peculiar habit of closing his office door in the middle of the afternoon and changing into his pajamas for a 30-minute nap. Odd as it may sound, this practice contributed to his ability to work effectively for extended periods.

NASA conducted scientific studies that showed a 26-minute nap could enhance a pilot’s performance by 34%. Another study found that a 45-minute nap could boost cognitive abilities for up to 6 hours. This evidence supports the idea that our brains have a physiological need for naps.

Statistically, there are more accidents during certain times of the day when people are naturally drowsy.

Many genius inventors, both women and men, have stories of making breakthroughs in their research while asleep. The author shares an example of Dmitri Mendeleev, the creator of the periodic table of chemical elements, who found inspiration for his work during his sleep.

The type of learning that benefits the most from sleep is procedural learning. An experiment involving two groups of students highlights this fact.

Sleep plays a crucial role in the learning process, while a lack of sleep can harm cognitive functions significantly. The author shares the latest research findings that emphasize how sleep deprivation affects functions beyond sleep itself.

One striking example involves a 30-year-old man who, despite being physically fit, experienced sleep deprivation for 6 days, sleeping about 4 hours less each night. This disrupted his body’s chemical balance to the point where it resembled that of a 60-year-old person. To restore his body’s chemistry to its original state, he would need a full week of good-quality sleep.

To wrap up this chapter in Brain Rules, John Medina suggests aligning individuals’ biological rhythms (chronotypes) with their study or work schedules. This could involve incorporating napping into business and education to better suit people’s natural sleep-wake cycles, which may not align with the typical 8 a.m. start time.

brain power

Rule No. 8: Stressed brains don’t learn the same way

John Medina demonstrates that the relationship between stress and learning can be straightforward and not necessarily harmful. An experiment based on Stanislavsky’s approach (immersing oneself in fear) with theater students from the University of California at Los Angeles reveals that stress can affect the immune system.

Another story involving stress is that of Judith, a teenager from an underprivileged neighborhood who had a difficult early childhood. Surprisingly, she became a well-liked high school student, excelled academically, and appeared to have no lasting psychological scars.

Individuals vary in their response to stress due to their uniqueness. Scientific evidence suggests that the most significant predictor of academic and professional success is the emotional stability within the family.

As Brain Rules, John Medina highlights three crucial factors for assessing work-related stress: the type of stress, the balance between motivation and boredom, and the equilibrium between personal and professional life.

In reality, stress itself is not harmful; it’s a natural defense mechanism of your body designed for short-term responses to significant but temporary dangers.

The potential problem arises when stress becomes chronic due to a problematic and consistently tense environment, whether in your family, at work, or in social situations.

The takeaway from this eighth rule is that it’s important to regain control over daily stress to enhance productivity. Additionally, strategies to minimize boredom should be considered because boredom itself can be a source of stress that dulls the brain.

Creating boundaries between your personal and professional life, like mandatory firewalls, can be beneficial. We know that stress in one area can affect the other, and it can turn into a harmful cycle that may lead to depression.

Rule No. 9: Sensory integration 

Have you ever noticed the fascinating effect that occurs in movies? The visual images on the screen, combined with sounds coming from different directions, make you believe that the sounds are actually coming from the actors’ mouths.

This phenomenon, still a subject of scientific study, is referred to as synesthesia. It’s a peculiar aspect of how our brains process information, almost like a circuit breaker for our neural systems.

In simpler terms, synesthesia happens when our senses receive an overwhelming amount of information. John M. illustrates this with examples like a nightclub environment, where various sensory inputs like noise, lights, physical contact, emotions, smoke, and alcohol all come together.

The author presents two scientific theories:

The author presents two scientific theories about how our senses work:

  1. In the first theory, our senses operate independently and send their information to a central command center.
  2. In the second theory, our senses collaborate right from the start, consulting and influencing each other.

The focus here is on the moment of perception, which becomes particularly interesting when it doesn’t function correctly (as studied by Oliver Sacks).

Once sensory information is received and fragmented, the question arises of how it gets organized to form our mental representations. Rule number 9 explores this process, highlighting that while we can pinpoint where it happens, explaining exactly how it works is more challenging.

Imagine a team of experts analyzing incoming data, such as visual information for reading. They meticulously identify the shape of each letter (like recognizing the curve of a ‘U’ or the lines of a ‘T’). This process demands considerable effort and time, which is why reading can be a relatively slow way to integrate information into the brain.

This complexity in information processing explains why two people in the same situation can perceive entirely different things. The brain’s attempt to simplify information can sometimes lead to confusion.


In one type of synesthesia (there are more than 50 types), a peculiar phenomenon occurs: even if the brain’s wiring is damaged, the senses continue to cooperate. This means that visual information can influence perceived sounds, even when there are no actual sounds present!

Now, the question arises: does having multiple senses involved enhance the learning process? The author mentions the work of Richard Mayer, an expert in multimedia learning, which outlines key principles regarding how visual and auditory senses collaborate during learning.

However, there’s a trap to be aware of. It’s a common mistake to think that bombarding the brain with additional information during learning will optimize the process. John M. uses a metaphor involving a hiker to illustrate this point: believing that wearing two heavy backpacks would help the hiker reach their destination faster than just one!

The particularity of the olfactory sense (the Proust effect)

Imagine taking a journey into the brain of a young soldier who, after seemingly surviving the psychological impact of war in Vietnam, decides to study medicine. However, on his very first day in the operating room, he suddenly runs out, screaming. What could have caused this unexpected reaction?

The answer lies in the unique way our brain processes smells. Scientists have long known that a single odor can trigger a flood of memories, even ones from the distant past. John M. explains this phenomenon in detail.

In a nutshell, our sense of smell is different from our other senses because olfactory receptors lack the protective layers that other sensory receptors have. They go directly to their destinations in the brain, bypassing the usual sorting center known as the “Thalamus.” This is unlike our visual and auditory receptors, which have protective barriers like the cornea and eardrum.

So, the suggestion here is to expand your learning experiences beyond the usual visual and auditory information. Embrace a wider range of sensory stimuli to enhance your learning and memory.

Rule No. 10 : Vision trumps other senses 

I come from Bordeaux, France, a place known for its wine culture, and this relates to John Medina’s Rule No. 10. The American author shares a story about wine experts who were tricked by European neuroscientists at Bordeaux University of Enology.

In the world of wine, there’s a specific vocabulary for white and red wines, and experts never mix them up. In this experiment, researchers added a harmless red dye to white wine and fooled 54 professional tasters. Surprisingly, they all used the vocabulary of red wine to describe it. This experiment illustrates the significant influence of visual cues over other senses when they share the same space and time.

The researchers concluded that “the nose smells what the eyes see,” and John Medina explains the biological reasons behind this phenomenon.

The retina in your eyes is like a bustling movie studio with many crews filming their own movies.

These “films” are sent to the occipital cortex, the brain’s visual processing headquarters. What you perceive isn’t a direct and entirely accurate projection of reality but rather an assembly of multiple “films” that your brain pieces together.

This process explains why we sometimes experience visual hallucinations, where our brains invent stories that don’t align with what our eyes see. Your past experiences play a significant role in shaping these mental representations, and vision accounts for half of your brain’s activity.

When it comes to learning and memory, images are much more effective than words. This phenomenon is called the “picture superiority effect.” Studies have shown that images presented for a few seconds can be recalled with a 90% success rate even after several days, making visual information easier to remember than text. You can even try this experiment at home!

When researchers conducted similar tests using text and spoken words, the recall rate dropped significantly to just 10%. The reason behind this phenomenon is quite logical: the brain processes words as if they were composed of numerous tiny images.

To understand this better (as per rule no. 10), imagine walking into a museum where each letter is treated as a separate work of art. This insight sheds light on the way we read. In the brain’s view, words don’t really exist; they are simply collections of miniature images.

In addition, the chapter includes a simple experiment involving a baby to illustrate how our brains process visual and auditory information. John Medina also shares how his career choice was influenced by a Walt Disney character, Donald Duck, in the film “Donald in Mathmagic Land.”

Rule No. 11: Gender, male and female brains are different

Prejudices can hinder a society’s progress and harmony. Both men and women contribute to a balanced perspective, combining attention to detail with a broader view, which enhances overall productivity.

Finally, in Brain Rules, John Medina delves into a historical perspective, going back at least 2,400 years to the time of Aristotle, the renowned philosopher who was the mentor of Alexander the Great. Aristotle once made the statement, “The female is an impotent male.”

John shares a story about a fictional assistant director at an airport. The narrative is based on a study that observed how corporate staff members perceive male and female assistant directors. The findings were clear: when a man holds the position, he is typically seen as competent and friendly. However, if a woman occupies the same role, she is often viewed as competent but labeled negatively with words like “bitch.”

Spotlight on biology

The X chromosome is a critical carrier of genes involved in brain development. Men possess only one X chromosome, while women have two, with one serving as a backup.

John Medina uses a vivid analogy by comparing the fierce competition of one sperm out of 400 million to find and fertilize an egg during sexual reproduction to a scene from “Star Wars.” Notably, the X chromosome is carried by only half of all sperm cells, but it is present in all eggs.

Medina highlights three key gender differences: genetic, neuroanatomical, and behavioral. To clarify, he uses the example of King Henry VIII’s quest for a male heir through multiple marriages.

In human reproduction, 46 chromosomes (twisted filaments known as DNA) are needed, equally contributed by the mother and father. Two of these chromosomes determine sex: X and Y. At least one X chromosome must be present from both parents for conception. Two X chromosomes result in a female, while one X and one Y chromosome lead to a male.

The determination of a child’s sex is primarily influenced by the father, thanks to a gene called SRY (Sex-determination Region of Y chromosome) located on the Y chromosome. However, it’s important to note that by default, human embryos tend to develop as females, challenging the notion of male dominance in human evolution.

The wholesale slaughter of myths continues

The notion that creative people are right-brained while logical and analytical individuals are left-brained is dismissed by John Medina as nonsense. He likens the brain’s two hemispheres to the sides of a ship, each with its own functions but both crucial for overall functioning.

Dr. Deborah Tannen’s research demonstrates that girls and later women often use eye contact and extensive conversation to build relationships. In contrast, boys tend to bond through shared physical activities and actions.

Medina emphasizes that our brains can trick us into misinterpreting scientific findings, leading to the misconception that boys compete while girls cooperate. In reality, both boys and girls engage in cooperation, although boys may do so through competitive activities.

So, how do you apply this knowledge in the reality of everyday life?

Applying this knowledge to everyday life involves understanding and managing the emotions of both women and men. For teachers and business professionals, this is a daily practice. The author offers some ideas to become more effective and efficient in this regard:

  • Recognize the utility of emotions.
  • Understand that men and women process emotions differently.
  • Acknowledge that these differences arise from a combination of nature and nurture.

Rule no. 12: We are natural explorers

“Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime.”
[Chinese proverb used by the author to summarize the general idea of this rule] 

Do our learning abilities decline as we age?

Recent discoveries challenge the idea that our brain’s capacity gradually diminishes with age. Scientists have found evidence that the brain continues to generate new neurons, even though many are lost every day. These new neurons are created in regions of the brain associated with learning.

Staying curious and continuously stimulating our minds helps create new networks of neurons, altering the brain’s structure and function based on our experiences. Curiosity serves as the fuel for ongoing brain development throughout our lives, regardless of age.

The conventional view of babies as blank slates has also shifted. Babies are now seen as models that help us understand how humans learn at any age. This change in perspective was influenced by research on the innate abilities of newborns, such as their responsiveness to simple actions like sticking out their tongues.

The final chapter introduces a learning method involving covering and uncovering objects, which can captivate a child’s attention for an extended period. This method aligns with our ancestors’ survival instincts, as they had to be alert to potential dangers in their environment, even when not directly visible.

Between 14 and 18 months of age, babies discover that their desires and preferences may differ from those of others. The author outlines seven rules characterizing this perspective, with the first being “If I want it, it’s mine,” and the last one being “If it’s mine, it’s mine.”

See and imitate, a game of mirror neurons

Let’s dive into the story of a monkey, some raisins, and how these elements led Italian researchers at the University of Parma to discover mirror neurons in the brain. These mirror neurons, like a reflection, mimic the actions of others and are now believed to exist in humans as well, scattered throughout the brain.

In human brains, mirror neurons are thought to be located in various areas. Each year, new insights into the brain’s workings, especially during early childhood, help us better understand these processes.

Addressing the question of whether learning abilities decline with age, Nobel laureates Edmond Fischer and Edwin Krebs, who were 72 and 74 years old at the time, affirm that curiosity remains a driving force for their brains.

To wrap up this final chapter, John Medina emphasizes that it’s quite easy to disrupt this positive cycle of development, something that has been happening in education and business management systems for centuries. He highlights the example of how children often associate school with grades rather than fostering a desire for curiosity. Similarly, employees may associate work solely with their salaries. John suggests ideas to promote and nurture curiosity at any age and in any environment, be it at school, university, or work.


Brain Rules reinforces, scientifically, more than five decades of curiosity towards understanding human cognition. This curiosity has been a driving force for personal growth and is shared here.

The book has been instrumental in dispelling misconceptions and myths that have caused much confusion. Examples include the fallacies of “like father like son,” the idea that multitasking can maintain focus, or the belief that activities like sports and music cannot be as valuable as work.

Upon revisiting the book, it became evident that emotional stimuli during childhood, something John’s mother effectively used in his upbringing, might not have been as prevalent in one’s own upbringing, perhaps due to parents’ demanding work schedules. The frustration lies not with one’s parents but with how our systems, be it education or business, have stagnated over the years despite advancements in neuroscience.

This divergence led to a decision to leave formal education at 15 and the corporate world at 33, embarking on a path of self-education. As the author states, there remains a significant gap between research, education, and the business world.

In essence, Brain Rules reaffirmed that the journey of developing one’s instinct as an explorer was on the right track. Referring to role models and mentors is akin to learning through mimicry, but learning from students and the surroundings is equally enriching.

What Brain Rules offers are 12 principles in the form of rules to enhance personal development and dispel misconceptions. It provides valuable insights to incorporate into daily life.

These resources should be a reference point for educators, parents, and entrepreneurs to apply effectively. Understanding human cognitive functions is crucial before adopting, transmitting, or forming any beliefs.

In summary, Brain Rules effectively popularizes current knowledge about the brain. The author’s goal is to make this knowledge accessible to a broader audience, facilitating personal growth and evolution.


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