While raising my own five children, I’ve learned though both experience and research that ages 0-3 are the most crucial years for brain development. Understanding the science of brain development will make it clear just how important this time is because of the massive synaptic pruning that begins occurring at 2-3 years of age. It’s a “use it or lose it” notion that lays the foundation for how their brains will function. Yes, genetics plays a role, but more importantly it is a combination of the child’s environment and experiences that leads to how their brains can become optimized to function to their fullest potentials for the rest of their lives.

Synaptic Pruning in Brain Development

When children are born, genetics will determine the roughly 86 billion neurons that fill their brains (which by the way are the same 86 billion neurons they will have as adults), but more significantly than the neurons themselves is how they are connected to each other. Neurons don’t actually touch each other, but send messages across a gap called a synapse. These synaptic connections are formed based on how children interact with their environment. The more signals sent between neurons, the stronger the connection grows.

In the image below, you can see the dark clusters which are the neurons and where they are starting to branch out which are the synapses. You can see that at 36 weeks gestation and as a newborn there are very few synapses, only about 2,500. Fast forward to 2-3 years of age, and the number of synapses explodes to its lifetime peak of about 15,000.

Reproduced from Seeman et. al: Human Brain Dopamine Receptors in Children and Aging Adults, Synapse 1987: 1:399-404. Copyright ©1987, Wiley-Liss Inc., a division of John Wiley and Sons, Inc. Reprinted by permission of John Wiley and Sons, Inc.

At this point, rapid pruning occurs and as you can see in the image above, by the time a child is four and six, there is a drastic reduction in synapses. The brain overproduces synapses at a young age so that it can fine tune itself according to the sensory input received from the child’s environment and experiences. This synaptic pruning is most dramatic when a child is three years old but continues through adolescence and results in a 50% reduction in synapses by adulthood.

Neuron Growth & Connections Over Time Source: Corel, JL. The postnatal development of the human cerebral cortex. Cambridge, MA: Harvard University Press; 1975

By the time children are three years old, their brains are 80% of their adult size, and by the age of five, their brains are 90% of their adult size. This is why it is absolutely crucial to provide children with the best opportunities for brain growth at a young age as their brains are creating the framework for all future learning.

Neurons: The Cornerstones of Brain Development

To further understand synaptic pruning at a deeper level, let’s take a look at where it all begins….with a neuron. A neuron is made up of four main parts. The dendrites receive information, the cell body processes that information, the axon carries the information from one part of the neuron to the other, and the axon terminal transmits the information to the next cell in the chain. A bundle of axons traveling together is called a nerve, and nerves can transmit information over long distances (from your brain to your big toe for example).

Photo Credit: Wikimedia Commons, By User:Dhp1080 – “Anatomy and Physiology” by the US National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) Program ., CC BY-SA 3.0

Dendrites are the part of the neuron that receives incoming signals. Based on the strength of this incoming stimulation, the neuron must decide whether to pass the signal along or not. If the stimulation is strong enough, the signal is transmitted along the entire length of the axon in a phenomenon called an action potential. This is when we say a neuron fires.

Synapses: How Brain Development Grows

The word “synapse” is derived from the Greek words “syn” and “haptein” that mean “together” and “to clasp”. The synapse is like a crossroads or a junction between neurons. Each neuron can form thousands of links with other neurons to make up to 1,000 trillion synapses in a typical brain. The more signals sent between neurons, the stronger the connection grows. The connections that are not used as often weaken. Synapses are basically what allows you to learn and remember. There are two types of synapses: electrical (which is less common) and chemical (which is more common).

Photo Credit: Wikimedia Commons, user:Looie496 created file (2009), US National Institutes of Health, National Institute on Aging created original / Public domain

Electrical synapses remain in their pure electrical state and cross the synapse using a gap junction as a short cut. In this way, one cell and one synapse can trigger thousands of other cells that can all act in synchrony. Something similar happens in the muscle cell of your heart, where speed and team effort between cells is crucial. But if every synapse in your body activated all of the neurons around it with electrical synapses, your nervous system would be overstimulated, maxed out, and exhausted. *Interesting Fact: Electrical synapses are much more abundant in embryonic nervous tissue where they help guide neural development. As the nervous system matures, many electrical synapses are replaced by chemical ones.

Chemical synapses are used more often, slower, easier to control, and are more precise and selective in what messages they send and where. Chemical synapses have the ability to convert an electrical signal to a chemical signal and back to an electrical signal to become an action potential again in the receiving neuron. In order to diffuse across a synaptic cleft, chemical action potentials need neurotransmitters, or chemical signals, to help deliver their message.

How the Brain Transmits Signals – Photo Credit: Wikimedia Commons (2013) Gif created from Inside the Brain: Unraveling the Mystery of Alzheimer’s Disease

Neurotransmitters

Depending on which particular one of the hundreds of neurotransmitters bind to the receptor, the neuron might get excited or be inhibited. Any region of a single neuron may have hundreds of synapses, each with different inhibitory or excitatory neurotransmitters. So the likelihood of that post-synaptic neuron developing an action potential depends on the sum of all the excitations and inhibitions in that area. When we look at some of the most common neurotransmitters, it becomes clear that the most stimulating thing for the brain is to be learning. This is why children crave stimulating environments where they can learn through play. (Source for Synapses and Neurotransmitters)

Excitatory Neurotransmitters excite neurons increasing the chances they will fire off an action potential.

• Glutamate is involved in more than 90% of all excitatory neurotransmitters and is associated with learning and memory. It interacts with four different receptors and has more opportunities to have messages successfully and quickly sent between nerve cells. This fast signaling and information processing is an important aspect of learning and memory. Glutamate also allows nerve cells to build associated information, which is the foundation of learning.  *An overabundance of glutamate can stress out the brain, however, and cause seizures and migraines which is why some people are sensitive to msg (monosodium glutamate) in their food.
• Norepinephrine is a familiar excitatory neurotransmitter that helps control alertness and arousal.

Inhibitory Neurotransmitters chill neurons out decreasing the chances that they  will fire off an action potential.

• GABA (gamma-aminobutyric acid) is the primary inhibitory neuron. It is known for it’s calming effect and plays a major role in controlling nerve cell hyperactivity associated with anxiety, stress and fear. GABA and glutamate act like and “on” and “off” switches and work in opposite ways. To have a properly functioning brain, a delicate balance between the inhibitory effects of GABA and the excitatory effects of glutamate. In fact, GABA is made from glutamate. GABA also works together with serotonin.
• Serotonin in an inhibitory neuron that affects mood, hunger, and sleep. Low amounts of serotonin are linked to depression.

Inhibitory and Excitatory Neurotransmitters play both sides and can either excite or inhibit depending on what type of receptors they encounter.

• Acetylcholine enables muscle action, learning, and memory.
• Dopamine influences movement, learning, attention, and pleasurable emotion.

When children get older, they might lack the motivation to complete school work or get good grades, but children ages 0-3 are wired to want to explore their environment. What looks like play to us is really the most effective way for children to learn. By providing children with a stimulating environment that allows for exploration of their world and a chance to play, it will help their brains to grow to the best of their abilities.

Myelnation: What Makes Brain Development Automatic

Myelnation is what creates automaticity in learning. For example, when you first learned how to read the word cat, you sounded out each letter, “c-a-t…cat”, but after sounding it out several times, you simply memorized that word as “cat”.

Every time an action potential travels through the axon of a neuron, the axon is coated with a myelin sheath. Mylenation both insulates the axon and increases the speed of the action potential. Myelin is made out of glial cells and wraps around the axon in a spiral fashion. Glial cells (also called neuroglia) are non-neuronal cells in the central nervous system and peripheral nervous system that support and protect neurons, maintain homeostasis, clean up debris, and form myelin.

Glial cells in the central nervous system (which is comprised of the brain and spinal cord) are called oligodendrocytes, and glial cells in the peripheral nervous system (which is comprised of autonomic functions and body movement) are called Schwann cells. Myelin is what makes up the white matter in the brain.

When an action potential travels through an unmyelinated axon to the corresponding synapse of another neuron, it moves like a wave, but in a myelinated axon, it hops through it like a portal.

When children experience something over and over and over, the myelinated axons will make these experiences automatic. Think of the brain like riding a bike and how people say, “you only need to learn how to ride a bike once.” So, the first time you get on a bike it’s completely foreign. You don’t know how to work the pedals or balance at all. The first few times of trying to manage the pedals and handlebars at the same time leave you shaking and wobbly at best, but slowly and over time you become more and more confident until one day you’re whistling a tune and looking of in the distance as your body expertly carries out the work.

Love Versus Neglect in the Developing Brain

Neurotransmitters aren’t the only chemical messengers in the body. The endocrine system is a set of glands that slowly releases hormones into the bloodstream.  Oxytocin, known as the love hormone, is important during early life for proper development of neural pathways. Maslow’s Hierarchy of Needs details the basic psychological and self fulfillment needs all humans need to thrive.

Maslow’s Hierarchy of Needs: By Saul McLeod, PhD | published 2007, updated April 04, 2022

The disturbing image below shows two brain scans. The first brain scan is of a normal healthy 3 year old child. The second brain scan shows a much smaller brain of a child who suffered extreme abuse and neglect.

Photo Credit: Dr. Bruce Perry, 2005, Maltreatment and the Developing Brain

In his article, Maltreatment and the Developing Child: How Early Childhood Experience Shapes Child and Culture,” Dr. Perry who is an internationally recognized authority on child trauma and the effects of child maltreatment explains that,

“In the most extreme and tragic cases
of profound neglect, such as when
children are raised by animals, the
damage to the developing brain – and
child – is severe, chronic, and resistant
to interventions later in life.

Children who are provided with a loving and nurturing environment with stimulating experiences will incorporate these elements into the framework of the brain, and this will lay the foundation for all future learning. Children who are raised in an environment of chaos, unpredictability, threat and distress, however, will have an adapted brain structure designed to survive in that environment that will not be best suited for future learning.

Brain Development in Romanian Orphans

In his NPR article, “Orphans’ Lonely Beginnings Reveal How Parents Shape A Child’s Brain“, Jon Hamilton explains how when the corrupt Romanian government was overthrown in 1989, the world was shocked to learn about the more than 100,000 children in government care that were left alone in their cribs, wallowing in their own filth, and with nothing but the white ceiling to stare at and the cries of the other babies to keep them company…for days and days and days. There was no one there to soothe their cries, no one there to hold them and give them affection, and no one there to talk to them and help them to interact with their environment.  The result was stunted growth and a range of social and emotional problems.

The odd behaviors, language delays, and range of other symptoms suggested problems with brain development, and so researchers began studying the children using a technology known as electroencephalography (EEG), which measures electrical activity in the brain. What they found were disturbingly low levels of brain activity. As the children grew, there were able to conduct MRIs on them, and it showed that their brains were actually smaller and that they had a reduction in grey and white matter. (The grey matter is the outer part of the brain and is  all of the neurons bunched together. The white matter is the inner part of the brain which is the myelinated axons that connect the neurons together.)

White Matter and Grey Matter – Photo Credit: Wikimedia Commons (2007) Suseno

In another experiment conducted after the orphaned children had been adopted, it showed that their brains could not discriminate the face of a stranger from the face of their adoptive mother. Because their brains were not able to identify with a loving caregiver at a young age, that part of their brain wasn’t developed, and then when someone was ready to give them love, they didn’t know how to accept it.  This is called reactive detachment disorder, and with lots of patience and love, it is possible to rewire the brain, unfortunately it’s just not very probable. Today, the system in Romania is still corrupt, and there are currently 70,000 children waiting for adoption. 🙁

Concluding Comments on Brain Development

Milestones such as a baby’s first tooth, transitioning to solid food, their first step, and sleeping through the night are important parts of the early years of development, but just as (if not more so) are the neural pathways that we are helping our children create that will lay the foundation for all future learning. So grab a book, get some flashcards, set up learning stations, and get down on the floor and play with your child because you only get one chance to lay the foundation…so make it count!

Resources for Further Research on Brain Development

Throughout this article, I’ve linked to my resources where appropriate, but I also read the following articles and watched the following videos that helped me to get a broad understanding of this topic. If you’d like to learn more about this topic, I highly recommend checking out some of these videos and articles.

• How the Brain Works – A 9 minute video by MsThinkology that does a wonderful job of explaining how the brain works.
• Neurons and How They Work  – A great 5 minute video by the Discovery Channel with great images that show how neurons work in the brain.
• Neurons, Synapses, Action Potentials, and Neurotransmission – This article by Robert Stufflebeam from the Consortium on Cognitive Science Instruction thoroughly explains how the brain works using language that is complex, but easy to follow with excellent graphics.
• Nurturing the Developing Brain in Early Childhood – This PowerPoint by Lisa Freund, Ph.D. from The National Institutes of Health in Maryland really sums up everything I’ve talked about in this article.
• Baby’s Brain Begins Now: Conception to Age 3 – This article by the Urban Child Institute goes into more scientific depth about why children are primed and ready to learn before the age of 3.
• Children and Brain Development: What We Know About How Children Learn – This article by prepared by Judith Graham, Extension human development specialist, and revised by Leslie A. Forstadt, Ph.D. Child and Family Development Specialist through the University of Maine offers a succinct explanation of how the brain works and provides lots of specific things that parents can do to help their children’s brain development.
• Brain Plasticity and Behaviour in the Developing Brain – This scientific article by Bryan Kolb, PhD and Robbin Gibb, PhD published in the US National Library of Medicine National Institutes of Health goes into thorough detail about the plasticity of the developing brain and discusses all factors that affect it.
• Why Practice Actually Makes Perfect: How to Rewire Your Brain for Better Performance – I really like this blog by Jason Shen because he does a wonderful job of explaining the importance of myelination.
• Discovering the Brain: The Development and Shaping of the Brain – Very thorough and in depth explanation of how a baby’s brain develops in the womb and how nerve cells know where to go and what to become.
• From Neurons to Neighborhoods: The Science of Early Childhood Development. – Great chapter about how experiences help to shape the brain and how important neonatal health is.