National Geographic : 2015 Jan
first year 63 a suckling baby is one of life’s great miracles, so is the transformation of that wobbly infant into a walking, talking toddler capable of negotiat- ing bedtime. While researching this story, I have watched that miracle unfold before my eyes as my daughter has gone from a fidgety bundle with only a piercing cry signaling hunger to a feisty three-year-old who insists on putting on her sunglasses before stepping out of the house. The blossoming of her mental and emotional abilities has been a string of marvels, deepen- ing my amazement at how deftly a baby’s brain comes to grasp the world. The milestones she has passed would be recognizable to any parent. At two she knew enough to realize that she didn’t have to hold my hand when walking on the sidewalk; she would reach for my hand only when we were about to cross the street. Around the same age, she also learned to block the drain in the bathtub with the ball of her foot—turning what was to be a quick shower into a playful bath. Before she turned three, she was holding lengthy con- versations and coming up with rhymes: “If the candy tastes bad, Willy Wonka will be sad.” Despite millennia of child rearing, we have only a limited understanding of how babies take such gigantic strides in cognitive, linguistic, rea- soning, and planning ability. The lightning pace of development in these early years coincides with the formation of a vast skein of neural cir- cuits. At birth the brain has nearly a hundred billion neurons, as many as in adulthood. As the baby grows, receiving a flood of sensory input, neurons get wired to other neurons, resulting in some hundred trillion connections by age three. Different stimuli and tasks, such as hearing a lullaby or reaching for a toy, help establish dif- ferent neural networks. Circuits get strength- ened through repeated activation. The sheath encasing nerve fibers—made of an insulating material called myelin—thickens along oft- used pathways, helping electrical impulses Natasha Alvarez floats in a swimming hole in Lancaster, Pennsylvania, hoping that a stress-free pregnancy will help her child’s brain development in utero. Yudhijit Bhattacharjee is writing a nonfiction book, The Spy Who Couldn’t Spell. Lynn Johnson’s feature, “Vanishing Voices,” in the July 2012 issue, was on the world’s disappearing languages.