Brain Development

The adult brain has a very large number of dendritic branches and synapses between cells that are organized in a very specific way. There simply is not enough space in the human genome to specifically encode all of this information. Instead of being only a passive "readout" of genetic information, normal development of the brain depends in part on the activity of the neurons themselves. Even while the baby is still in the womb, neuronal activity (the electrical firing of cells) is very important. For example, it has been discovered that the rhythmical waves of firing of groups of receptor cells in the eyes play an important role in helping to structure some parts of the brain involved in vision. This activity cannot be a response to visual input, since the eyes are closed at this age. Instead, it appears that one part of the nervous system can create a kind of "virtual environment" specifically to aid the formation of other, later developing, parts.