Your baby is born with most of the brain cells she will ever have, but during her first 12 months in the world, her brain will become increasingly complex. By the time she reaches the age of two, her brain will already be 75 percent of its adult weight. By the age of three, it will have reached 90 percent of its adult weight.
Almost 50 percent of the brain cells your baby is born with will wither and die during the first few years of life. This process, known as neural pruning, organizes the brain and makes it more efficient. The brain learns through experience. Events in your baby’s life trigger electrical impulses to the brain, establishing neural pathways. The more a pathway is used, the more established it becomes, making it less susceptible to pruning. Just like a muscle, the brain works on the principle of “use it or lose it.”
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?
- When your baby is born his brain weighs Synapse xt about 350 g (12 oz); by his first birthday it weighs 1 kg (2.2 lb).
- At birth, the brain already has some 200 billion neurons (nerve cells) – about the same number as it will have in adulthood.
- Each neuron responds to stimulation by growing a network of dendrites (branches) and synapses (connections) between itself and its neighbors.
- Each neuron ends up with dendrites leading to an average of 15,000 synapses.
- Dendrite formation becomes more complex over time, with third- and fourth-tier branches appearing by 6 months of age.
- The more stimulation the brain receives, the more sophisticated its dendritic networks become.
- 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.
- Between 2 and 4 months of age, the number of synapses in your baby’s visual cortex increases tenfold to 20,000 per neuron.
- By 12 months of age, neurons that distinguish native language have found their permanent position in the brain.
- At 18 months the language center of the brain experiences a massive synaptic spurt, producing an explosion in grammar.
What does this mean for your baby?
During the first eight years of life, and in particular the first three, there are a number of critical windows for acquiring specific types of intelligence. Once these windows have closed, learning is much more difficult, if not impossible. Babies are particularly open to learning during their first year, as outside of the brainstem (which controls critical life-sustaining processes), very few neural pathways have been formed.
Your baby’s emotions
The part of the brain responsible for processing emotions is one of the first to develop after birth. For the first few weeks, your baby’s emotional state will be fairly black-and-white – she’ll either be happy or unhappy. By 3 months, experience will have made her emotions more nuanced. As the frontal lobe of her brain grows from 6 months, your baby will begin to show a variety of emotional and social responses.
- Expression: Your baby will begin to make sense of his feelings in relation to his surroundings. Instead of simply crying, he may find another way to get your attention and so communicate his feelings.
- Inhibition: Your baby will start to be able to think twice about her behavior. For example, she may come to the realization that there is no point in crying every time you put her down to sleep.
- Stranger anxiety: Towards the end of the first year your baby may begin to show a fear of strangers. As the frontal lobe of the brain continues to develop, your baby’s experiences through the anxiety stage influence his social abilities in later life, helping to determine whether he is a shy or outgoing person. Frequent and positive social interactions cause synapses to fire in ways that help to hardwire the brain’s emotional and social intelligence.