Normally, as a cell begins its journey from a fertilized egg to a young nerve cell -- that takes about eight weeks-- it is exposed to a number of molecular signaling pathways that essentially nudge the cell toward becoming a brain cell and not, for instance, a liver cell.
"A cell has to make a set of decisions to ultimately end up at a very specific fate. I compare it with playing a music piece. You can play jazz and get the liver [cell], or you can play classical and get something else. By now we can do that for about 40 cell types, and nearly all the time we can go from the stem cell to the young neural cell, then to a specialized subtype of nerve cell."Of course, he doesn't actually expose developing cells to music, but the musical metaphor helps illustrate the complex process of cell development and how we can influence it. The metaphor can achieve reality during whole brain development in childhood when the brain cells are deciding how to fit in and what to do in their new universe inside your skull.