One great thing is that not only don't we use that many of them but they are not genetically engineered to do any one specific function. Thus the brain damaged person can train other areas to learn diferent tasks. There are some researchers who believe that there is a hydration factor w re to healthy vs unused or dead brain cells also. But remember all our cells everywhere in the body are being replaced as they age and die, by plan. I think it is said we are actually different/refreshed, cellularly every 7 years or so.