LET THE LEARNING BEGIN
Part of the scientific answer is that 100 billion neurons are "hard-wiring" the baby's brain -- each neuron is producing fibers that transmit signals to thousands of other neurons. For instance, when a 2-month-old baby tracks a toy with his eyes, it's a sign that areas of the brain relating to vision are "wiring up."
But each bit of information from the baby's environment, and each experience, reinforces particular neural connections. In the first two months alone, the number of these connections increases from an estimated 50 trillion to 1,000 trillion.
Compared with most other species, humans have a huge number of brain cells. "It's as if nature decided, We want to have these guys with enormous brains, but we can't make their bodies six times larger, so we're going to cut pregnancy short and get these things out before the head becomes too big," says Alan Leslie, Ph.D., a cognitive-development researcher at Rutgers University. As a result, human babies are born with immature brains, creating what Leslie calls "the great learning species."
The learning starts with the sounds and sensations a baby experiences right before he is born. At birth, the sense of hearing is more developed than vision. "Full-term infants have the benefit of having heard their mother's voice for the weeks preceding delivery," says Charles Nelson, Ph.D., professor of child psychology, neuroscience, and pediatrics at the University of Minnesota's Institute of Child Development, who has monitored newborns less than 24 hours old and found that when they hear their mothers' voice, they show a different pattern of brain activity than when they hear a stranger's.
Outward evidence of brain work is subtle at first: the newborn modifying his sucking to adapt to the breast, bottle, or pacifier; the 3-week-old baby who takes a break from feeding to look into her mother's eyes. Because a newborn's vision is believed to be no better than 20/400, he is more attracted to stark contrasts, such as black and white. But when the connections between the neurons in the visual cortex increase dramatically, between 2 and 4 months, an infant begins to see more clearly. That, plus his developing depth perception, may explain why he now notices more-detailed pictures and toys. By the time babies are 2 to 3 months old, they'll begin watching people as they walk across the room. By 6 months, vision improves to 20/40 or better.
Nelson believes that the ability to recognize caretakers, which occurs at about this point, is a primitive understanding of cause and effect: "When I'm hungry, one of them feeds me," posits the baby brain. An infant may look across the room toward the refrigerator, because she's learned that bottles come from there. Breast-feeding mothers are likewise objectified.
By 4 to 5 months of age, a baby will visually follow an object -- such as a spoon or a rattle -- when it falls out of her hand, which solidifies her growing understanding that things exist even in motion. Simple hiding games and rounds of peekaboo reinforce the idea that objects, and Mommy, still exist even when they're out of view.