Wiring The Brain
The effects of early experience are profound. The flood of sensory experiences drives the explosion of learning that takes place after birth. The brain undergoes a series of extraordinary changes in a display of biological exuberance. The electrical activity of brain cells change the physical structure of the brain. A child's earliest experiences can increase or decrease the number of cell connections in the brain by 25% or more.
- A baby is born with about 100 billion nerve cells, roughly as many as there are stars in the Milky Way.
- These cells are not well connected to each other. While the brain contains all the nerve cells it will ever have, the pattern of wiring between them has yet to develop and stabilize.
- These specialized nerve cells, neurons, are ready to form connections and networks.
|A busy baby|
- Every neuron can send impulses, axons, and receive impulses, dendrites, from other neurons.
- The axon of one neuron hooks up with the dendrite of another to form a synapse.
- Neurotransmitters, in the baby's brain, enable electrical impulses to travel across the synapse.
- "Learning" is this process of making the connections.
An explosion of connections occurs as the baby experiences the world around him. Axons and dendrites swell with buds and branches, like trees in spring. Young children's brains form twice as many synapses and consume twice as much energy as the brain of an adult. This profusion of connections lends the growing brain exceptional flexibility. If they are used, they become part of the brain's permanent circuitry.
A person who feels danger kicks out lots of a chemical called cortisol, which provides a burst of energy. That's bad news for a baby, because the part of the brain that's largely responsible for learning, the hippocampus, shrinks when hit with big doses of cortisol. The chemical also stunts brain cells ability to talk to one another by causing dendrites to atrophy. Babies who feel violence and neglect store these negative emotions as an "implicit memory" in the hippocampus, which means it's unconscious, and can be impossible to extinguish. Higher levels of cortisol levels have been associated with severely delayed development, and neglected infants develop many fewer synapses. Also, researchers have found that children who don't play much or are rarely touched develop brains 20% to 30% smaller than normal for their age.
|It's nature and nurture, baby!|
The Developing Embryo
- Potential for greatness may be encoded in the genes, but whether that potential is realized depends on patterns etched by experience in those critical first years of life. Modern neuroscience is providing hard, quantifiable evidence to this effect, that until now was largely anecdotal.
- The rhythmic firing of neurons is not a by-product of building the brain but essential to the process itself, and it begins well before birth.
- Neural activity triggers a bio-chemical cascade that reaches all the way to the nucleus of cells and the coils of DNA that encode specific genes.
- Nature is the dominant partner during the pre-natal phase of development, but nurture plays a vital supportive role. Changes in the environment of the womb can help or hinder the clockwork precision of the neural assembly line.