Failing memory was once thought to result simply from a progressive loss of brain cells as people get older, but that's no longer believed to be the case. Research now suggests that unless people have a disease that wipes out their brain cells, they die with the same number as they had when they were born. And although human brains do shrink in overall size — by about 10 percent during adulthood — that loss of volume isn't the culprit behind memory problems.
A combination of factors actually conspires to create the infamous "senior moments." These include a decreased effectiveness of communication between nerve cells that whizz information around the brain, increase of inflammation in brain tissue in response to infection and disease reduction in blood supply, and damage caused by exposure to free radical molecules such as oxygen throughout life.All these factors make up the recipe for the wear-and-tear type changes seen in the aging brain. Reflexes become slower, and it may take longer to finish a crossword puzzle. It's normal, although by no means universal, for people to experience these changes. Some people don't have even this level of deterioration and are as sharp as tacks well into their 90s (and even beyond).