Brain Development

At the same time that the brain is growing and increasing in size and complexity, regressive events are also occurring. One example is the elimination of synapses. During the process of synapse formation, the number of synapses increases above the level observed in the adult and remains at this level for some time. Then, synapses are eliminated until the adult number is reached. For example, in certain parts of the visual cortex the density of synapses per neuron reaches a peak of about 150 percent of the adult level at about age four months then starts to decrease at the end of the first year of life to reach the adult level by about age four. The timing of this process is different for different areas of cortex. In the frontal cortex, the peak level is reached at about one year of age, and it then slowly declines to reach adult levels sometime in adolescence. This loss of synapses does not reduce the range of behaviors but may be related to the stabilization of important networks of neurons in the brain.