One of the ironies of growing older is that just as one begins to acquire wisdom, senility may also be setting in. Most experts seem to agree that many of us will experience noticeable mental decline by age 65. After age 50 some important areas of the brain lose considerable numbers of neurons (Selkoe, 1992). But it is not clear how such alterations in size and density relate to mental function, or whether these or other organic shifts influence the rate of cognitive decline. However, by the age of 65-74, 3% of the population have some cognitive impairment and by 85, nearly half may be demented (Hachinski, 1992).
Some of the more specific , non-disease, changes in the brain have been studied and summarized by Selkoe (1992). He states that structural and chemical modifications that typify the aging brain become apparent in late middle life, in the 50s and 60s. By the 70s some of these changes have become even more pronounced. He believes that as individuals grow older, the overall number of brain neurons decreases, but the pattern is supposedly not uniform. The neurons seem to disappear at different rates depending upon the area of the brain. Selkoe (1992) also maintains that not all neuronal changes are necessarily destructive. Some may represent attempts by surviving neurons to compensate for loss or shrinkage of other neurons and their projections.
Selko (1992) has listed some of the brain structures involved in learning, memory and reasoning, that normally undergo a number of anatomic changes later in life that can potentially impair cognition.
Cerebral Cortex: Large neurons shrink and amyloid deposits develop in extracellular spaces.
Thalmas: Selected Neurons shrink or die
Basal Forebrain: Acetylcholine-secreting neurons shrink or die
Amygdala: Amyloid deposits develop in extracellular spaces and neurofibrillary tangles develop within neurons
Hippocampus: Large neurons shrink or die...