YOUR CHILD'S BRAIN

Brain research shows that healthy brain development is largely a product of positive interactions with parents, family, and caregivers. These interactions are beneficial influences on the kind of child and adult your baby will become.

Your baby's brain begins to grow soon after conception, so the nine months of your pregnancy are clearly an important period for the healthy brain development necessary for your baby's well-being. What may not be as obvious is that the first three years of your child's life are also a window of opportunity during which her brain is more responsive to positive influences than it ever will be again. To understand why this is true, a few facts about early brain development are necessary. Below is a brief summary of how your baby's brain develops during your pregnancy and in the following years, followed by a discussion of why this time is so critical for healthy cognitive, emotional, and social development.

First Trimester
Brain development is set in motion about three weeks after conception, when the neural plate, a group of specialized cells in the outer layer of the embryo, folds over onto itself to form the neural tube. Soon the neural tube begins to transform into the brain and spinal cord.

About 8 weeks after conception, the first neurons appear. These specialized nerve cells continue to be formed at a remarkable rate-as high as 250,000 per minute in some areas of the brain-until about halfway through your pregnancy. After each neuron is created it must migrate to its final position in the developing brain, a journey which can take up to 30 hours.

In these first few months, neurons begin to make the connections-called synapses-which allow them to send and receive information, although for the time being synapse formation remains slow compared to the rates it will later reach. By the eighth or ninth week after conception, the nervous system has matured enough to allow the fetus to make its first movements, but these are mostly reflexive and involuntary. They can be detected by ultrasound, although in most cases they cannot be felt by the mother.

Second Trimester
The simple group of cells which made up the neural plate has become a brain. It now includes the major regions which make up the adult brain; although still immature, they are visible using magnetic resonance imaging (MRI). By the end of the second trimester, your baby's brain has already created more neurons than it will ever need-so many more, in fact, that as many as half will eventually die and be absorbed by other cells. This genetically controlled process, called programmed cell death, is both natural and desirable, since it helps the brain become more efficient. From this point on, the most important aspect of brain development will be the creation of synapses.

Third Trimester
In the last months of your pregnancy, feelings, memory, and thought are already at work in your baby's brain. These processes, sometimes referred to collectively as executive function, are largely controlled by the cerebral cortex-the outer layer of the brain. Synapse formation is reaching its peak in this region in the third trimester, and the consequences for your baby's development are dramatic. Her movements become more intentional and goal-directed. She is affected by sounds such as voices and music, and can already demonstrate an early form of learning. For instance, she can distinguish her mother's voice from other voices and the sounds of her native language from those of foreign languages. These apparently simple feats are actually important milestones in her cognitive development.

The First Three Years
Your baby may not walk or talk for most of her first year, but don't be fooled: her development is proceeding at an astonishing rate. She is making important advances in thinking and reasoning, and is learning cognitive skills which adults take for granted. For example, the vision- and memory-related areas of her brain are growing in power, partly as a result of increasing numbers of synapses. This improves her ability to recognize objects and remember actions, both of which are necessary for sophisticated learning.

In the second year, connections between the thought-related and language-related structures of the brain are improving, and the number of synapses in these areas is continuing to multiply. As a result, your baby is becoming more aware of himself as an individual, and is increasingly able to use reason. By the end of second year most children undergo a dramatic increase in the number of words they can understand and use. The precise timing of this vocabulary explosion varies among children, and is strongly influenced by the amount of language they hear at home.

This vocabulary explosion is an excellent example of how a child's surroundings shape her development, especially in the first three years. When your baby is born, her brain already has all of the neurons it will ever have, and most of them have finished migrating to their appropriate locations. But its development is far from complete. At this point the brain is like a new house whose electrical system has not been completed: There is a complex network of wires in place, but only a few of the wires have been connected to each other and to the various outlets and fixtures which require power. Although most of the structural work is complete, the system needs fine tuning before it can perform all of its tasks.

This fine tuning is affected by your child's environment. Her brain prepares itself by creating an excess of synapses, the connections which allow it to send and receive information. Then, in the first years of life, it begins to eliminate synapses which are not used. Scientists describe this process as a period of blooming followed by a period of pruning. Although the precise timing varies among different areas of the brain, the first three years appear to be the most critical period for synapse elimination. How does the brain decide which synapses to keep and which to prune? Although genetic factors play a role, environmental influences are extremely important. These range from positive experiences (such as good parenting, maternal warmth, and language exposure) to negative ones (like stress, domestic violence, and neglect).

The people in your child's environment are especially important. Research shows that healthy brain development is encouraged by positive interactions with parents, family, and caregivers; these relationships help decide the kind of child and adult your baby will become. Looking into your baby's eyes, talking and singing, repeating her sounds and facial expressions, and other loving interactions are ideal ways to help her brain grow. For older children, conversation and shared reading time are essential. For more information about how you can promote optimal brain development for your child, see the Parenting and Language and Literacy sections of our site.