How our brains grow
We’re each born with as many brain cells as the Milky Way has stars—approximately 100 billion of them. These brain cells cells, known as neurons, form connections that are called synapses. They divide and multiply like wildfire, creating new cells and and forming even more connections. In a positive, healthy environment, the brain explodes with growth until around age 3.5.This frenzy of growth slows and levels off after that, but it doesn’t stop. By mid- to late childhood, a typical brain contains twice as many synapses as it did at birth.