Understanding Brain Development in Young Children (continued)

What the brain has done is to lay out circuits that are its best guess about what is required for vision, language, etc. Now the sensory experiences must take this rough blueprint and progressively refine it. Circuits are made into patterns that enable newborn infants to perceive their mother's touch, their father's voice and other aspects of their environment.

Normal sensory experiences direct brain cells to their location and reinforce the connections between brain cells. We are born with more than 100 billion brain cells or neurons; we will not grow more. That's about 10 times the number of stars in the entire Milky Way, and about 20 times the number of people on the planet.

Neurons are the functioning core of the brain. Each cell body is about one-hundredth the size of the period at the end of this sentence. A neuron has branches or dendrites emerging from the cell body. These dendrites pick up chemical signals across a synapse and the impulse travels the length of the axon. Each axon branch has a sac containing neurotransmitters at its tip. The electrical impulse causes the release of the neurotransmitters, which, in turn, stimulates or inhibits neighboring dendrites, like an on-off switch.

These connections are miracles of the human body. But to understand their power, you have to multiply this miracle by trillions. A single cell can connect with as many as 15,000 other cells.

This incredibly complex network of connections that results often is referred to as the brain's "circuitry" or "wiring." Experience shapes the way circuits are made in the brain.

A remarkable increase in synapses occurs during the first year of life. The brain develops a functional architecture through the development of these synapses or connections.

For example, if a parent repeatedly calls a child a certain name, then connections will form that allow the child to recognize that name over time as referring to him and he will learn to respond. From birth, the brain rapidly is creating these connections that form our habits, thoughts, consciousness, memories and mind.

By the time a child is 3 years old, a baby's brain has formed about 1,000 trillion connections — about twice as many as adults have. A baby's brain is superdense and will stay that way throughout the first decade of life. Beginning at about age 11, a child's brain gets rid of extra connections in a process calling "pruning," gradually making order out of a thick tangle of "wires."

The remaining "wiring" is more powerful and efficient. The increase in synaptic density in a child's brain can be seen in Figure 2. The interactions that parents assist with in a child's environment are what spur the growth and pattern of these connections in the brain.

As the synapses in a child's brain are strengthened through repeated experiences, connections and pathways are formed that structure the way a child learns. If a pathway is not used, it's eliminated based on the "use it or lose it" principle. Things you do a single time, either good or bad, are somewhat less likely to have an effect on brain development.

When a connection is used repeatedly in the early years, it becomes permanent. For example, when adults repeat words and phrases as they talk to babies, babies learn to understand speech and strengthen the language connections in the brain.

Figure 1. Neurons and connections

Figure 2. Synaptic density in the human brain

Construction of the Brain

We have explored how the brain develops at the cellular level with neurons and connections. Understanding the different parts of the brain as a whole and how it functions and develops also is useful.

The brain grows in sequential fashion, from bottom to top, or from the least complex part (brain stem) to the more complex area (cortex). If you draw a line from the forehead to the chin and open the brain for a side view, you would see the brain as it is shown in Figure 3.

Figure 3.Brain: side view

The basic elements of the human brain include the following:

1. The brainstem is at the base of the skull and it controls most basic life activities, including blood pressure and body temperature.

2. The midbrain is at the top of the brainstem and it controls motor activity, appetite and sleep.

3. The cerebellum is behind the brainstem and it coordinates movement and balance.

4. The limbic system is in the central part of the brain and it controls emotions, attachment and memory.

5. The cortex is the top layer of the brain and is about the depth of two dimes placed on top of each other. The cortex is the "executive branch" of the brain that regulates decision-making and controls thinking, reasoning and language.

The cerebral cortex contains 80 percent of the neurons in the brain. Because it is the least developed part of the brain at birth and keeps developing until adolescence and even beyond, the cortex is more sensitive to experiences than other parts of the brain.