Old Cells in the Brain operate a little different from newer cells.

http://www.sciencedaily.com/releases/2009/03/090302091235.htm

In a lot of neural degenerative diseases, protein buildup in the nerve cells cause disruption of signals. The body has a mechanism of breaking down the proteins. When there is more oxidative stress on the body the body needs to eliminate even more proteins which could lead to neural disorders such as Parkinson and Alzheimer's disease. Researchers have learned that BAG-1 and BAG-3 proteins play an important role in regulating protein degradation during the aging process. BAG-1 regulates the protein degradation process when we are young but as we get very old a switch occurs and BAG-3 regulates the protein degradation process. It is postulated a dysfunction in the molecular switch could be the reason why we there are so many neural degenerative disorders as we age. Something must be going wrong in the BAG-3 that is leading to the accumulation of proteins which are causing these devastating diseases.