Aging of the Brain

During aging the brain undergoes a number of changes.  Cell numbers decrease continuously and the amount of dendritic branching of cortical neurons decreases.  The number of amyloid plaques increases.  Despite these changes, there is remarkably little effect on cognitive function.  Alzheimer's disease is not a direct consequence of the normal effects of aging.  Rather, the disease should be seen as an abnormal consequence of these changes.  For example, amyloid plaques are commonly found in the brains of aged individuals.  However, it may be the reaction to the presence of amyloid (ie., the generation of neuritic plaques, in which dystrophic neurites and gliosis are seen to occur around the amyloid deposit) which starts the pathogenic cascade.