'Wait, I know the right word, it's ... '

Some people are born with better-than-average memories, but almost everyone experiences changes in their power to recall once they reach their 40s. Many of us may not be as quick to remember a name, or we may struggle to come up with just the right word in conversation.

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This on the tip-of-the-tongue frustration is often more apparent after 50, when the brain becomes less adept at retrieving information.

But thankfully, forgetting names or losing car keys from time to time are such common memory glitches that they aren't considered signs of worse things to come, explains Dr. Ron Petersen, director of the Alzheimer's Disease Research Center at the Mayo Clinic.

New research by scientists at Harvard University shows that key genes affecting learning and mental function begin to deteriorate at age 40, which could explain why it gets tougher to remember things spontaneously when people hit midlife.

"In the healthy 50-year-old brain, information is getting in, but they’re having a problem with retrieval," says neuropsychologist Dr. Paul Nussbaum of the University of Pittsburgh School of Medicine. "It's like going into a library to retrieve a book and they can’t find it."

Information overload
Another reason for mental lapses could be that middle-age brains are overloaded with information, some experts say.

"We weren't built to remember more than 50 people at a time, let alone hundreds or thousands," says Dr. Barry Gordon, a professor of neurology and cognitive science and director of the Johns Hopkins Memory Clinic.

Then there's the stress of juggling families and hectic careers that can trip up people as they get older.

"Americans are doing far too much at once and our attention reserve has a hard time focusing," says Nussbaum. "We’re not sleeping enough. It’s a multitude of factors that result in a 50-year-old brain having memory problems."

Researchers at the Yale Medical School recently found that when people are in stressful situations, an enzyme in the brain is activated, impairing short-term memory and other functions in the prefrontal cortex. Memory loss has also been linked to depression and anxiety.

"Memory is vulnerable and sensitive," says Nussbaum. "Pain, not enough sleep, anything can set it off kilter."

Aside from trying to reduce stress and get enough sleep, Petersen, a member of the Alzheimer's Association medical and scientific advisory council, says there are other ways to compensate for memory inefficiencies that strike in midlife.

"We have to pay more attention and concentrate more when we're learning new information and events," he says. "If we spend more time and are more mindful when we learn someone's name to try to get it more firmly in our memory, we can do it."

Part 3: How much forgetfulness is too much?