Science of Early Learning

How your baby’s brain develops

Humans are the only animals whose brains triple in size during the first two years of life. If it were any larger at birth, a baby’s head would not fit through its mother’s pelvis. Any smaller, and the baby’s survival would be in jeopardy. So how does the brain grow to 75 percent of its adult size by the age of two, and 90 percent by the age of three?

1. When your baby is born his brain weighs about 350 g (12 oz); by his first birthday it weighs 1 kg (2.2 lb).
2. At birth, the brain already has some 200 billion neurons (nerve cells) – about the same number as it will have in adulthood.
3. Each neuron responds to stimulation by growing a network of dendrites (branches) and synapses (connections) between itself and its neighbors.
4. Each neuron ends up with dendrites leading to an average of 15,000 synapses.
5. Dendrite formation becomes more complex over time, with third- and fourth-tier branches appearing by 6 months of age.
6. The more stimulation the brain receives, the more sophisticated its dendritic networks become.
7. The frontal lobe (the part of the brain that deals with emotions) becomes highly metabolically active from 6 months of age. By 18 months the neural foundations of your baby’s emotional intelligence are laid.
8. Between 2 and 4 months of age, the number of synapses in your baby’s visual cortex increases tenfold to 20,000 per neuron.
9. By 12 months of age, neurons that distinguish native language have found their permanent position in the brain.
10. At 18 months the language center of the brain experiences a massive synaptic spurt, producing an explosion in grammar.

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