Memory Impairment & Aging
The brain contains about 100 billion neurons. A common misconception is that tens of thousands of neurons die each day. In reality, few neurons die over a person's lifetime, but they do shrink. This shrinkage may partially explain why mental functioning slows in middle and older age. (Serious memory problems do occur when major disorders such as a stroke or Alzheimer's destroy whole clusters of neurons.)
In addition to the shrinkage of neurons, starting in middle age the brain begins producing smaller quantities of many neurotransmitterschemical messengers that relay information between nerve cells. Brain blood flow is also reduced 15 to 20% between ages 30 and 70, although the shrinkage of neurons may account for the reduced flow because less tissue requires less blood.
Cultural attitudes and preconceptions about aging and memory loss can also influence the occurrence of memory lapses as people age. In one study, researchers compared the memory skills of two groups known to harbor few stereotypes concerning old agethe people of China and deaf Americanswith those of a third group known to have numerous preconceptions about aginghearing Americans. Among these preconceptions is the notion that aging causes an inevitable decline in memory skills.
The study results suggest a strong link between culture and memory: The first two groups were less forgetful than the third group, and older Chinese participants performed as well as the younger people in each of these groups. The implication is that if people expect their memory to get worse, they may be less diligent in trying to remember.
Other research indicates that the mental processes required to remember newly acquired information are the same as those needed to retrieve memories from long agosomething most older people do quite well. This implies that older people retain the capacity to recall recent events, but the new information is not being recognized as important or is being discarded instead of stored.
Some researchers interpret this to mean that occasional memory lapses may result from a failure to pay close attention to the information rather than an inability to remember. Thus, it appears that forging new memories depends in large part on staying interested, active, and alert.