The family of four sat in the doctor’s office. “There is something wrong with Eric,” the father said sadly. “His mother, younger brother and myself enjoy competitive sports. Eric would rather stay home and read or work on his computer or sit in the bleachers with his iPad. And he’s often sick.”

The doctor smiled at 17-year-old Eric and asked kindly, “What’s your perspective?”

“I know they think something is wrong with me,” the boy replied. “Hey,
I love my family but they are so exhausting. Take yesterday. We all went for a five-k run before breakfast.

After that it was the gym for a fast game of basketball. Mid-afternoon it was a three- hour community softball game and then a quick swim before dinner.

The evening was spent playing pool and board games with friends.

I can do some of those activities with them, but not all. My tongue was hanging out before we even got to the soft-ball game!”

“We’ll start with a physical exam and go from there,” said the doctor. His
initial impression was that, although Eric was underweight for his height, most other measures were within normal limits.

“My differential diagnosis is that Eric’s brain has a bent toward introversion, while you three have bents toward extroversion.”

Looking at four puzzled faces, the doctor explained that extroversion, ambiversion and introversion (EAI) are terms for three different types of naturally occurring brains.

EAI describes the way in which each brain chooses to focus its energy and attention and indicates the amount of stimulation in the environment that is optimum for that brain.



Extroverts have an external focus and thrive in a stimulating
environment. They actually derive energy from interacting with the external environment..


Introverts have an internal focus and prefer a less stimulating environment. Too much stimulation can actually drain their energy over time and contribute to illness.


Introverts have an internal focus and prefer a less stimulating environment. Too much stimulation can actually drain their energy over time and contribute to illness.

“Typically, you are most comfortable and energy- efficient when your brain is in an environment that matches your innate bent,” said the doctor. “If you are willing and interested, there is a simple screening assessment that may validate my impression.”

Eight days later, during their next appointment, the doctor reviewed the family’s assessments. Sure enough, mother, father and younger brother had scored at the high end of extroversion. Eric had scored high on introversion.

“So there isn’t anything wrong with my brain,” Eric said. “I just have a bent toward introversion. What a relief!” The adolescent was actually smiling.

His father said, “Please forgive us, Eric. We had no idea your brain was so different from ours.”

EAI describes the way in which each brain chooses to focus its energy and attention and indicates the amount of stimulation in the environment that is optimum for that brain.


This brain gets energy from a stimulating environment and recharges quickly by interacting with the outer world; therefore, it tends to spend energy freely. On the other hand, its energy is drained by an under-stimulating environment. It prefers more variety and intensity and less depth, requiring frequent breaks when trying to focus and often moving from one activity to another quite quickly. It tends to be competitive and may perceive no reason to play a game unless the players keep score, because that adds to the stimulation.

Metaphorically, the extroverted brain possesses a special protective callus, as it were, much like those on the fingers of string players that allow them to play without pain. Consequently, this type of brain can function in situations and environments of high intensity and danger that would be too overwhelming for other brains.

Short, direct, fast pathways pass through the extrovert’s brain reward system and areas of sensory processing. Its primary fuel is dopamine, the feel-better chemical that is linked with many addictive behaviors. If life is not going particular well, this puts the extroverted brain at higher risk for anything that increases the level of dopamine, including addictive substances and behaviors.

An introverted parent can be overwhelmed with an extroverted child and his or her need for continual variety and stimulation. The parent can put too much pressure on the child to “calm down”, and fail to make provision for him or her to get the needed stimulation. This increases the risk of the child becoming restless, bored and irritated, along with an increased risk of getting into trouble in a search for stimulation. Arranging for the child to spend time with safe extroverted children and adults can be of enormous help.

“I have this personality, where I’m a natural introvert in my personal life, but when you give me a camera and microphone, I have a so much to say.”
Eli Drake


The introverted brain can become exhausted when forced to spend large amounts of time in stimulating environments. It recharges by interacting with its inner world but it takes longer to recharge so it tends to spend energy cautiously. Introverted brains tend to be very alert when fully awake, thus they seek the least amount of stimulation in order to avoid being overwhelmed. If overstimulated its energy is drained and it can become tired, depressed and even sick, which may be a way of subconsciously avoiding additional environmental stimulation.

Metaphorically, this brain is like a camera with a wide open aperture that allows it to absorb the most data per second. Fortunately, it also has a special shut-off feature that allows it to block out additional incoming sensory data to allow time to process what has already been absorbed. In many cases it prefers to be an “observer” more than a “participator”; and when playing a game with others, would prefer not to keep score and just “play for fun”.

Typically this brain ends to do well at tasks that require an ability to pay attention and sustain it over time. No surprise it tends to do better at lower-stimulation and high-attention activities, such as accounting or working as a traffic- control officer in an airport tower.

An extroverted parent with an introverted child can put too much pressure on the child to “be involved”, and fail to protect the child from too much stimulation, which increases the likelihood of him/her getting sick.

When you’re partnering with someone who’s wired the opposite as you, it’s important to remember that your natural instincts are going to seem like foolishness to them.”



The ambiverted brain is moderately alert when fully awake. It tends to function best with average levels of stimulation: not too much and not too little.

It possesses neither a callus nor the ability to block out additional input.

Although less dramatic, it can also become sick from prolonged overstimulation.

Not much is yet known about the pathways or the fuel preferred by ambiverted brains.

No surprise, it tends to do well at tasks of moderate stimulation that require average amounts of attention.

“There is no such thing as a pure introvert or extrovert. Such a person would be in the lunatic asylum.

Carl Jung

alteration of


Eric pointed to the printed information the doctor had distributed and asked, “What does ‘alteration of incoming sensory data’ mean—in common ordinary language, that is?” Everyone chuckled.

“To explain this,” said the doctor, “you need to understand a tiny brain organ known as the thalamus. If you have ever gone to an emergency department because you’ve been injured or become ill, especially after regular working hours or on the weekend, there was likely someone called a ‘triage nurse’ who asked you what the problem was and directed you to the appropriate department.

“The thalamus is located between the ‘reptilian’ 1st brain layer and the ‘mammalian’ 2nd brain layer. Its job is to direct sensory data that you have taken in through your eyes, ears, nose, mouth, skin, etc., to the appropriate decoding centre so you’ll be able to make sense of them. In the process of directing this sensory traffic, the thalamus alters the incoming data—for two types of brains.”

The doctor paused and then asked, “Eric, do you prefer crowded, noisy environments or large crowds of people or…?”

Eric interrupted. “Heck no! I’m most comfortable with just a few people who I know well.”

The doctor looked at Jon, Eric’s older brother, who promptly said, “Me? I like to do some dirt biking or playing exciting computer games by myself, but something is always happening when a big group of people get together.

The more the merrier! I tend to get bored if nothing much is going on.”

“Blessed are those who do not fear solitude, who are not afraid of their own company, who are not always desperately looking for something to do, something to amuse themselves with, something to judge.”

~ Paulo Coelho

“In an extroverted brain,” the doctor explained, “the thalamus miniaturises incoming sensory data.

That means that in terms of brain stimulation, people seem ‘smaller’, objects seem less large, sounds seem ‘softer’, and lights appear less bright.

This results in reduced stimulation so the extroverted brain not only can take in more stimulation but also craves more stimulation in order to stay awake and alert.”

“That’s Jon’s brain, all right,” said their father with a chuckle.

“In an introverted brain,” said the doctor, “the thalamus magnifies the data so that, in effect, the brain is working with larger-than- life everything.

In terms of brain stimulation, people seem ‘bigger’, objects seem larger, sounds seem ‘louder’, and lights appear ’brighter’. The brain can easily become overwhelmed with the enlarged data.

Consequently, it withdraws from too much stimulation. Introverted brains may like people very much, but prefer to take them in smaller quantities.”

“And that would be me,” said Eric, almost proudly. “It’s a relief and kind of cool to know that I have a unique brain.”

That in itself is a turnaround, the doctor thought to himself. Amazing what a little knowledge can do!