Stages of Brain Development - from before birth to 18
The brain does not develop at an even pace. It tends to develop in waves with different parts of the brain developing at different times. This development takes place, however, in a predictable sequence. Neuroscientists have shown that the brain is affected by environmental conditions throughout the entire process of development, even prior to birth. This includes the type of nourishment, care, surroundings and stimulation the feotus or infant receives. This article gives a fascinating summary of the development which takes place in your child’s brain a) before birth, b) during their infancy and c) beyond their third year.
At conception the sperm and egg meet to form a single cell determining the genetic potential. About 60% of the genes are dedicated to brain development.
It is these genes that drive the early stages of brain development.
Three to four weeks after conception a thin layer of cells forms on the embryo. The cells fold and fuse to form a liquid filled tube. This is the basis of the brain and spinal cord. The embryo then starts to produce nerve cells or neurons. In the first month following conception the cells in the neural tube start to multiply at an astonishing rate, reaching a maximum of 250,000 neurons a minute. Most of the brain’s lifetime’s supply of cells are produced by six months.
At 14 weeks very few of the brain cells are sparked to perform a function. The majority begin to migrate to form different areas of the brain. Most cells arrive at the correct site at the right time. Those which are damaged or go astray tend to die. “In very rare situations some do reach the wrong location and form the wrong connections with the result later seen in eventual disorders such as severe infantile epilepsy, autism, some forms of intellectual delay and a vulnerability to develop schizophrenia.”
The brain produces many more cells than it will need. By the time the fetus is twenty weeks old, about half of these cells are deliberately shed.
The remaining cells are organised into forty different physical areas that will broadly govern senses and skills such as vision, language and muscle movement.
Brain Development in the Infant
By birth the brain has developed the total 100 billion brain cells, or ‘neurons’, it possesses. However the brain is a work in progress. Most of the neurons are still immature. The cells need to be activated and the connections between neurons are weak or have not yet been formed.      Â
  Brain at Birth                  Brain at 3 years          Â
                
        The pictures above illustrate how the neurons at birth are mostly unconnected to each other, but by age 3 years have formed dense connections.
At birth the infant can see, hear, smell and respond to touch . Almost immediately after birth the newborn’s brain begins to form trillions of connections and pathways between the neurons. These connections and pathways are vital as they enable the infant to see, hear, smell, learn and reason in a more developed way.
Although genes begin the process of brain development, it is the experiences of the child that now start to take over this process. These experiences trigger the electrical activity necessary to enable the brain to develop connections and grow.
These connections are called synapses. The connections are formed by each neuron putting out a long tentacle like fibre called an axon. The neuron uses the axon to send messages to other neurons. The messages are sent as electrical signals and picked up by thousands of short, hair like fibres could dendrites ( also produced by the neurons).
Each neuron is able to connect up with thousands of other neurons.
Repeated experiences cause the connections to become well worn pathways, permanently etched into the brain. Infrequent experiences result in the loss of developing pathways.
As the brain structure develops, the child will begin to reach the milestones associated with child development, such as grabbing an object, learning to speak, crawling and walking.
It is the combination of these neurons, synapses and pathways that will combine to form the unique structure and chemical composition of every individual’s brain.
Below are brain scans at different stages of development.. The dark patches are areas of densely connected brain cells.   Â
By eight months of age the average infant, living in a stimulating, secure and loving environment, will have sparked 500 trillion of these connections.By the age of two an infant has developed around 1000 trillion of these connections - twice as many as the parents. Although the connections continue to form throughout life they have reached their highest density (15,000 synapses per neuron). The root brain structure, which provides the foundation for future functioning, are largely established by the age of three. By then the foundations for thinking, language, aptitudes and attitudes, have been laid down and the structure and design of the brain is almost complete.
Beyond the Age of Three - Practice makes Permanent
In the early years the brain establishes many connections and pathways. The repetition of an action or experience helps to etch these pathways into the brain. Once they have become strengthened sufficiently, they become permanent.
From the age of 10 until late adolescence, the brain begins to prune some of these connections. Those connections which are not sufficiently strong, have been neglected or are used infrequently are lost. Strong connections are exempt from this process.
By the age of 18 the number of connections has been reduced to around 500 trillion - the same number the young adult had as an 8-month old.
The resulting brain is less able to adapt but is stronger and more powerful.
These connections remain largely stable in adulthood giving each person a unique pattern of mind, thought and emotions. It is this pattern that determines who we are, and will influence how we think and learn as adults.
“A baby born with a potential for greatness encoded in his genes may turn out to have a gift for logic or a brilliant criminal mind, the direction defined by his early experiences.” - Nash, J.M. (1997). How a child’s brain develops. Time Magazine, 3 February.
