The Amazing Human Brain and Human Development

Lesson 1: Beginning with the Human Brain

Brain Basics

A cross-section of the human brain. Image courtesy of Bruce D. Perry, M.D., Ph.D.
A cross-section of the human brain. Image courtesy of Bruce D. Perry, M.D., Ph.D.


Welcome to The Amazing Human Brain. The lessons in this course will teach you how the incredible mass of tissue in our skulls functions to make us the thinking, talking, feeling creatures we are.

Please take a minute to log on to the Message Board and tell the class what brings you to the course. Are you a professional caring for children, or a parent with a traumatized child? The Message Board will serve as our discussion forum throughout the course, and it can be a great tool in this "e-classroom" environment.

Let's start with some basics.

Think About It

Your brain weighs about three pounds. These three pounds, composed primarily of water and fat, allow you to walk and talk, to laugh, cry, and touch, to love and hate, to create and destroy. Everything you do, think and feel, every wish, dream, regret, and hope you experience is mediated by your brain. By sensing the world around you -- storing some fragment of each unique moment, cataloguing, sorting, organizing, and acting on your experiences -- your brain defines you.

It is your brain that allows you to be connected to other human beings in the present. It is your brain that links you to the past through language, religion, economies, and technologies -- all of which essentially reflect the distilled experiences of thousands of generations of our ancestors. And it is also your brain that connects you to the future if you have children and pass elements of your own life experience to them through your example and teaching. Finally, it is your brain -- and the brains of other people throughout history -- that has allowed humankind to create what we know as humanity.

No Science Background Required

Throughout this course, I will provide you with information about the brain's structure and function. This knowledge will create a framework for understanding the impact that maltreatment or trauma may have on the developing child. Don't worry if you're not a "science person." The majority of professionals working with maltreated children do not have a background in biology or the neurosciences, either.

An understanding of the rudiments of human brain function and brain development can provide very useful and practical insight to the all-too-often puzzling emotional, behavioral, cognitive, social, and physical problems that caregivers, parents, teachers, and others face when working with maltreated children.


A Brainy Factoid

You probably wouldn't be surprised to learn that the largest brain on earth belongs to the gigantic sperm whale, weighing in at a massive 20 pounds. But consider that the human brain, at a measly three pounds, is still approximately two percent of a person's body weight. The poor sperm whale (who cannot take brainy courses on the Internet) has a brain that represents only 0.02 percent of its weight!

The Brain's Prime Directives

Think about the following phenomena in the animal kingdom. What single explanation can account for these amazing animal abilities?

  • Sharks sense blood in water miles away.
  • Dogs hear very high-pitched sounds.
  • Geese navigate thousand-mile migrations, somehow sensing magnetic fields of the earth.
  • Hawks see the movement of prey from hundreds of feet in the air.
  • Bears detect scents from miles away.
  • Snakes sense body heat.

You guessed it! Each one of these unique capabilities is mediated by the animal's brain. Their brains' capacities to sense, process, and act are designed to help them survive -- to find food, to avoid threat, to procreate, and to ensure the future of the species.

The human brain is programmed similarly. Without the unique properties of the brain, humankind would have become extinct long ago. Our brain helps us survive and thrive while we develop. Once mature, our brain allows us to create, protect, nurture, and teach the next generation. Like the animal brains we just considered, the human brain is designed to help us survive, procreate, and become caregivers.

Evolution Takes Time

Species evolve slowly. Human evolution is no exception. The structural and functional capabilities of the human brain were selected to promote survival tens of thousands of years ago. When the human brain was evolving, there were no computers, electricity, cars, books, or even language, as we know it.

When the human brain was evolving into its current form, humans lived in "primitive" hunter-gatherer bands of about 40 people. For 99 percent of the time that we have been Homo sapiens, our ancestors lived in these very small groups. Nomadic migration, cooperative hunting, and foraging for non-cultivated fruits and grains characterized human lives. It is in these historical roots that the brain's key capabilities evolved and became modified and refined in order to ensure the survival of the species.

Think of how human life has changed in the last 10-thousand years or so. The social structures, economies, communications, technologies, and manifestations of abstract creativity that now characterize human life were obviously not present when the human brain was evolving. In many ways, the complexities of the modern world pose tremendous and unfamiliar challenges to a human brain designed for a different world.


The Brain's Prime Directives

Our brain's design makes it possible for us to survive, procreate, and become caregivers. These three prime directives have ensured the continuation of our species.

The Brain's Key Actions

Despite its complexity, the brain maintains some key actions. The brain senses, processes incoming signals, stores elements of this information and input, and acts on the incoming information.

How information enters, and is processed by, your brain. Image courtesy of Bruce D. Perry, M.D., Ph.D.
How information enters, and is processed by, your brain. Image courtesy of Bruce D. Perry, M.D., Ph.D.


In order to keep us alive, the brain uses a set of sensory organs (eyes, ears, nose, tongue, skin) to tell us some of what is going on in the outside world. Remember, we can't hear like a dog, smell like a bear, or see like a hawk. In fact, when compared to the rest of the animal kingdom, human senses seem quite limited.

  • Our ears hear sound only within a certain range
  • Our eyes see light in the visual range but not infrared or ultraviolet light
  • Our perception of touch requires a certain level of pressure
  • Our sense of smell only helps us if a scent is powerful or nearby

Despite these limitations, our powerful human brains can still integrate the information from all of our different senses and use it to create an internal representation of the external world.

Everything we experience is filtered by our senses. All sensory signals (sound, sight, taste, touch) initiate a cascade of processes in the brain that alter brain structure and function. This process of creating some internal representation of the external world (i.e., information) depends upon the pattern, intensity, and frequency of neuronal activity produced by sensing, processing, and storing signals.

Experience creates a processing template through which all new input is filtered. The more frequently a certain pattern of neural activation occurs, the more indelible the memory becomes. All living organisms have mechanisms to sense and respond to changes in their environments. These mechanisms respond continually and are designed to keep our body's systems in a state of equilibrium or homeostasis.

We have sensory mechanisms to tell the brain what is going on in the internal world of the body. For example, we have special sensory apparatuses that tell the brain the concentration of oxygen in the blood. Other systems sense the concentration of salts (e.g., too much salt causes a sensation of thirst) or gases such as carbon dioxide. These internal sensory mechanisms, like the five senses for the external world, help the brain continuously monitor and act to maintain life.


Once our sensory apparatuses has translated physical or chemical information from the outside (or inside) world into neuronal activity, this set of signals travels up into the brain to be processed. Sensory information from the external environment and the internal environment enters the central nervous system at the level of the brainstem and midbrain.

As this primary sensory input arrives, it is matched against previously stored patterns of activation. If the pattern is unknown, or is associated with previous threat, the brain will activate a set of responses that are designed to help promote survival. (This alarm response is at the heart of the post-traumatic symptoms seen in so many maltreated children.)

The human brain, divided into its four interconnected areas. Image courtesy of Bruce D. Perry, M.D., Ph.D.
The human brain, divided into its four interconnected areas. Image courtesy of Bruce D. Perry, M.D., Ph.D.

Your Brain is Conservative

Throughout life, the brain is making memories that correspond to various sights, sounds, smells, tastes, and movements. It creates templates of experience against which all future experience is matched. In this regard, the brain is a conservative organ. It does not like to be surprised. All unknown or unfamiliar environmental cues are judged to be threatening until proven otherwise.

Therefore, what you recognize as safe and comfortable has only become so through your experience. Something in your safe and comfortable present moment matches the associated, stored memories of previous safe, pleasing, or rewarding experiences. The same theory applies to feelings of terror or threat.

Sensory integration (putting the sight, sound, smell, and feel of an event together) is a crucial step in healthy development. There can be disruption of this capacity by even minor "timing" errors. If the signals coming from the neural systems responsible for hearing do not get into the thalamus and cortex in a synchronous way, there can be confusion, disorganization, and abnormal functioning. (See sidebar.)

Incoming Signal

At each level of brain organization, the incoming signal (called afferent) is categorized. When the brain compares incoming information to previously stored patterns, mistakes sometimes occur. For the Vietnam vet, a loud firecracker can induce a startled response and anxiety even though he knows it is only a firecracker. The incoming loud sound is categorized in the brainstem as being previously associated with threat and danger even before the signal can get to the cortex.

At each level of processing, a categorization process takes place. This immediate, localized processing can be crucial for survival. Your brainstem and spinal cord will tell you to withdraw your hand from a fire even before your cortex knows that you have been burned.

Another key step in processing experience is organizing information. Because the brain cannot possibly create a unique neural imprint or pattern of change to store every element of every experience, the brain stores "template" patterns based upon the first set of organizing experiences. All future incoming input is matched against these stored templates and, if sufficiently different from the original pattern, the brain will create a memory reflecting that difference.


Inherent to the processing of information coming into the brain is the capacity to store elements of these incoming signals. At the heart of our survival neurobiology is the capacity to make and store internal representations of the external world. Internal representations are your memory. The ability of the brain to create memories is due to the capacity of neurons and neural systems to change from one homeostatic state to another. Neuron and neural system changes are "use-dependent," only occurring if a new or extreme situation forces them.

This has important implications for understanding how we "create" memories of traumatic experiences. For adults, most experiences have only a small component that is new or unique. Typically, the majority of places, faces, words, sounds, smells, tastes, etc. in any given moment are familiar. In the classroom, for example, a lecture may result in cortical activation but will cause little new emotional, motor, or arousal activity.


You will recall that the neuronal pathways sending signals into a brain area are called afferent. The pathways sending neuronal signals out are called efferent. These efferent pathways regulate actions resulting from the process of sensing, processing, and storing incoming signals. Your brain mediates and controls the actions of your body. By regulating and directing the activities of the neuromuscular, autonomic, endocrine, and immune systems, your brain controls your every move.

Coming Up

Stay tuned for Lesson 2, where we'll learn about brain organization and parts like the cortex, and who MacLean was in the world of the brain.

Again, don't hesitate to use the Message Board for any questions you come up with as we move through the course. It's not every day you'll read about, say, the medulla , and not at all surprising that you might have questions about it.

See you in Lesson 2.


Sensory Integration Dysynchrony

Imagine watching a poorly dubbed foreign film. It's disorienting, isn't it? That's because the sound and movements don't match. It is likely that several developmental disorders include elements of sensory integration problem. Indeed, many infants and young children with these problems have a terrible time with lots of noise, chaos, action -- they become overloaded and may hold their hands over their ears, crawl into the fetal position, yell, or initiate self-soothing behaviors (e.g., rocking).

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