Using MRI and other imaging technologies, researchers have learned that your brain starts to get smaller as you get older. "The volume of the frontal cortex, which is responsible for reasoning, problem-solving and strategic tasks, gets smaller, and white matter gets more porous; it's not as tightly woven as it was," explains Denise Park, PhD, director of the Center for Vital Longevity in Dallas.
These changes may explain why most people experience subtle declines in the rate at which they process new information, the amount of information they can process at a time and the ability to remember new information long-term.
Memory of the past can also be affected. "As you age, it gets harder to put tags on individual memories, which allows them to be distinctive and easier to retrieve later on," says Tom Hess, PhD, professor in the department of Lifespan Developmental Psychology at North Carolina State University in Raleigh. This change in memory functioning appears to be due to age-related loss of neurons in the hippocampus, the area of the brain partially responsible for establishing new specific memories.
With age, protein deposits may start to form in the brain. The brain naturally produces a type of plaque called amyloid, which normally degrades and is eliminated by the body. Researchers have noticed a buildup of this protein during autopsies on people who had Alzheimer's disease. Up until very recently, it wasn't possible to look at plaque in healthy people, but Park and her team have been able to inject a radio tracer substance into the brain, then use imaging techniques to see whether healthy volunteers have a buildup of amyloid. They've found that between 25 and 35 percent of healthy adults start to have amyloid buildup in their 40s and 50s. Park notes that the plaque is associated with some cognitive decline but that it's uncertain whether it's an early sign or stage of Alzheimer's disease. "Lots of people functioning at a high level have this plaque that's associated with Alzheimer's," she says.
Growing older isn't all bad news for the brain. Every time you learn something new, new wiring gets laid down. The result: more processing power. You can also fight the aging of the brain.
Aging without question has its foundations in genetically determined mechanisms. "But," points out João Pedro de Magalhães, "genetics can be modulated by environmental factors." I'll give you a good example. One of the markers of aging that you'll be hearing a lot more about in this book are telomeres. Telomeres are the tail ends of chromosomes, the structures that carry genes. Every time a cell divides, the telomeres stabilize the cell's chromosomes, but in the process they become shorter. When telomeres become too short, the cell can no longer divide and it dies. This is believed to lead to various aspects of aging, including diminished muscle strength, wrinkles and lowered immunity. How much telomere length really affects longevity—if at all—is still unknown, but many prominent researchers believe it's an important cog in the wheel of life. In 2008, researchers at King's College in London looked at the length of the telomeres in the white blood cells of twins. Some of the participants were very active, while their twin siblings were quite a bit less active. The results of the study showed that, across the board, telomere length was related to activity: the more active the person, the longer the telomeres. When very active exercisers were compared directly to their less active twins, they had telomere lengths that looked to be about four years younger. Here was a case where genetics were the same, but the cells were influenced by differing external factors, in this instance, exercise.