YOUR UNIQUE BRAIN AND ITS DEVELOPMENT

Every working day, I write a post or an article for Linked In, all with some learning about the brain and how it can be applied in your life. I thought it could be useful for some readers to have an article discussing some brain fundamentals on how the brain develops from conception to make you the unique person you are. 

The basic building blocks of the brain

Neurons, dendrites and axons

A neuron is a specialised type of cell found predominantly in the brain and the central nervous system. A neuron has two special features - firstly it is electrically excitable and secondly, it connects using synapses. A typical neuron is divided into three parts: the cell body (or soma), dendrites, and axon. Dendrites look like branches of a tree and contain the receptors that receive the chemical messages, known as neurotransmitters, from other cells. The number of dendrites per neuron can vary from just one or two up to over a thousand. Neuroscientists suggest that the number of dendrites provides an indication as to the functional complexity of the neuron. Axons are fine strands that extend from the soma along which electrical messages are passed. They can be more than a meter in length where they pass down the spinal cord, which itself consists of millions of axons. Axons are protected by a myelin sheath, which helps the transmission of the electrical current and insulates them in a similar way to plastic surrounding electrical cabling. At the end of the axon are axon terminals which convert the electrical messages from the soma into chemical neurotransmitters that are then released into the synaptic gap to communicate with other neurons.

Synapses

Synapses are the gaps between the neurons. To communicate, the electrical signal from one neuron must jump across these gaps. Your brain achieves this by turning the electrical signal into a chemical message at the axon terminal. These chemical messages can only be received by a neuron with a matching receptor in much the same way as a jigsaw works – the “tab” pieces will only fit into the “slot” spaces of a matching jigsaw piece. Unlike the toy, the synaptic network is amazingly complex. Each neuron can establish connections to thousands of other cells in the body with the number of connections reaching a peak by the time you are around three years old.

The development of the brain

No two brains are the same. Just as your fingerprints and retinas are unique, so is your brain. It all begins in the womb when around seven weeks after conception your first neurons and synapses begin to develop in your spinal cord. During the next few months your brain will develop to eventually reach around 86 billion neurons (1). About 60 days before you are born, each neuron begins to establish connections with other cells in the body. In some cases, these connections are electrical and in other cases chemical. The number of connections each neuron will establish will vary from a few thousand up to 100,000. By the time you are three, you will have an average of around 10,000 synaptic connections for each neuron.

Your three year old brain is like a rain forest

To put this incredible amount of connections into perspective, suppose that the Amazon Rain Forest, which consists of roughly 2.4 million square miles of forest, contains around 86 billion trees. Each tree will have around 10,000 leaves. Your brain is therefore akin to all the leaves in the Amazon Rain Forest making it by far the most complex organ in your body.

Pruning

However the number of synaptic connections in the brain peaks in early childhood, around the age of 3 and as you move from being a baby to becoming a toddler, the process of synaptic pruning begins. The synaptic connections you use on a regular basis become stronger, and those that you do not use get weaker, or even disappear altogether.

By the time you are 16 you will have lost around half of your synaptic connections and the basic foundation of who you are, your character and your values will have been established. Psychologists call this the imprint period. Although your personality may be relatively well established, this does not mean that it does not change thereafter. Your brain’s ability to continue to reorganise the neural pathways in the light of experience is referred to as neuroplasticity.

 The process of synaptic pruning continues into early adulthood, not surprisingly as the prefrontal cortex does not reach full maturity until around mid 20s. As you learn and change the way you approach things, you also develop new synaptic connections. So although the overall number of synaptic connections tends to decline throughout your life, the nature of the connections within your brain is constantly changing. New connections are formed on an ongoing basis and some connections are lost as part of the brain’s normal process of forgetting. The synaptic network of connections is constantly rewiring itself based on your thoughts and experiences.

Is the brain like a muscle?

Some neuroscientists have begun to describe the development of the brain as analogous to the development of muscles, as it strengthens with use or, more specifically, the areas that are used most strengthen relative to those that are used less.

As evidence of this, a University College London study of the brains of London taxi drivers in 2000 found that they had larger posterior hippocampi than most people, which the researchers attributed to the extensive amount of navigational memory required for their work (2). This has led researchers to conclude that the brain develops through the combined effects of both nature (those aspects you inherit from your parents) and nurture (those that result from your environment and experiences). This is due in large part to neuroplasticity which I will explain in a future article.

The brain as a road network

I often use the analogy of a road network rather than a muscle as it helps to explain that the connections within the brain get stronger rather than the brain itself. Imagine that all roads in a newly developed area start off the same size (same number of lanes, same width etc.) and that they are made wider or narrower depending on usage. If they are not used at all then they are dug up and houses built in their place. Some roads therefore turn into 15 lane super-highways while others become minor back-streets.

We use our superhighways more frequently than the minor back streets and they give rise to more automatic behaviour, habits, strengths and flow.

What do you find most intriguing about your amazing brain?

 Photo by Hans-Peter Gauster on Unsplash

 1: Herculano-Houzel, S. (2016). The Human Advantage: A New Understanding of How Our Brains Became Remarkable. Cambridge. Massachusetts. MIT Press.

2: Maguire, E. A., Gadian, D. G., Johnsrude, I. S., Good, C. D., Ashburner, J., Frackowiak, R. S. J., & Frith, C. D. (2000). Navigation-related structural change in the hippocampi of taxi drivers. Proceedings of the National Academy of Sciences of the United States of America, 97(8), 4398–4403.