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Forgetfulness and Stress

  • Chris Woolston, M.S.
  • Posted March 11, 2013

It's hardly surprising that tough times can stimulate the brain. Back in our hunter-gatherer past, quick thinking was a survival skill. Whether tracking a gazelle or meeting a deadline, we need to stay mentally sharp in times of stress.

As Stanford University stress expert Robert Sapolsky explains, stress can literally energize the brain. The body responds to stress by releasing sugar into the bloodstream and sending extra blood to the brain, essentially giving brain cells a feast of energy. Meanwhile, the stress hormone cortisol helps alert the hippocampus, a part of the brain that's crucial for storing and retrieving memories. A little stress also sharpens all of the senses, making it possible to remember smells, tastes, and sounds that otherwise might have gone unnoticed.

For better or worse, it doesn't take much stress to get our brains humming. Our systems are so sensitive that a plot twist in a book can open up the adrenaline floodgates. Adrenaline, by the way, is what makes those sad, poignant, or frightening scenes in the book so memorable. As Sapolsky reports, people who take adrenaline-blocking drugs such as the beta-blocker propranolol often can't remember emotion-packed details much better than mundane details.

A double-edged sword

When its important to cram large amounts of information into our brains in a short time -- a favorite practice of college students -- stress can definitely work to our advantage. As reported at a meeting of the Society for Neuroscience, one study found that medical students preparing for a stressful exam did especially well on a task that required memorizing random numbers.

But stress didn't make them universally smarter; the students performed poorly at word games and logic puzzles. Later, after the exams were over and the students were more relaxed, the results were reversed: They could easily handle logic puzzles but had trouble remembering meaningless numbers.

So while short-term stress can sharpen some sorts of learning and memory, it can't turn the brain into a foolproof recording device. Under stress, a person may become focused on certain details while ignoring others. When introduced to a stranger, many people are too worried about making a good impression to spend energy on little details -- like remembering the person's name.

Memory and trauma

In an unfortunate twist, our worst moments also tend to be our most memorable. Someone who has been robbed at gunpoint may never be able to forget the glint of the handgun. If a child has to huddle in the basement during a hurricane, he may still be able to recall the roar of the wind in his adult life. And if a war veteran has seen combat, he may be haunted by memories of the moment his buddy was hit by a nearby mortar shell.

A moment of terror or stress tends to rev up both the mind and body. A body under extreme stress releases adrenaline and cortisol, instant-energy hormones that speed up the heart, tense up muscles, and shift key parts of the brain into a higher gear, a process that helps sear stressful moments into memory. But these moments may survive only as isolated fragments of a memory, surfacing in terrifying flashbacks, dreams, or intrusive thoughts, with whole sections hazy or missing.

A war veteran may always remember the sound of an explosion, for example, but he may not remember where he was or what he was doing before the blast. An inability to remember important details of a trauma, in fact, is one of the hallmarks of post-traumatic stress disorder (PTSD).

Perhaps surprisingly, some memories of traumatic events may not even be true. As Harvard psychologist Richard McNally reports in the Canadian Journal of Psychiatry, the mind is highly suggestible and memories are extremely flexible. While experts agree that highly stressful events are rarely forgotten completely, specific details can become blurred, confused, and even unintentionally fabricated over time.

Too much of a bad thing

Our brains can help us get through stressful moments, but we're not well-equipped to face stress over the long haul. After just 30 minutes of continuous stress, the body stops sending extra blood to the brain. As a result, the brain no longer has a jolt of sugar to keep it especially alert and focused.

When those half-hours of stress add up to days, stress hormones can start to gum up the memory banks in the hippocampus. As Sapolsky reports, just a few day's worth of injections of these hormones can temporarily impair memory in healthy human volunteers. In rat studies, as stressful days turn to stressful weeks, the connections between nerve cells in the hippocampus can start to shrivel. When connections break down, cells have a hard time communicating with each other, making it difficult to collect the scattered bits of information that form memories. Stressed-out humans and rats can still store new memories, but it's apparently harder to do so. The connections between nerve cells can grow back and make it easier to remember things, but this may occur only if there's a chance to relax.

Scientists are still trying to understand exactly how stress affects the mysterious realm of memories, but the message seems clear: We can all protect our brains by managing stress effectively. In the words of UCLA's Center on Aging, ''a systematic approach to relaxation exercises and avoiding unnecessary stressors will lead to diminished anxiety, better recall, and possible slower brain aging.''

To deal with stress, some people change their lifestyles; others have to change their attitudes. Some people dont have that luxury or ability, but it is possible to make small changes in the way you manage your day that can make a difference. For example, you could try taking 5 minutes to close your eyes and meditate, walking around the block for 15 minutes at lunchtime, or scheduling time to decompress for half an hour every day. Whatever approach you take, you'll be doing your brain a favor.

References

Mayo Clinic. Stress: Constant stress puts your health at risk. September 11, 2010.

Sapolsky RM. Why Zebras Don't Get Ulcers. Third Edition. Henry Holt and Company, New York. 2004.

Ohio State University. Anxiety good for memory recall, bad for solving complex problems. 2004.

McNally RJ. Debunking myths about trauma and memory. Canadian Journal of Psychiatry.

UCLA Center on Aging. Minimize stress to maximize memory. 2001.

McEwen B and Lasley EN. The End of Stress As We Know It. Joseph Henry Press, Washington, D.C. 2002.

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