When Your Memory Plays Tricks on You

5 min read

March 15, 2001 -- Ever wonder why Dustin Hoffman's autistic character in Rain Man could memorize every name and number in the phone book, but thought that a candy bar and a car each cost 50 cents?

"Autistic individuals don't use context to enhance their memory and learning the way most people do," David Beversdorf, MD, an assistant professor of neurology at Ohio State University in Columbus, tells WebMD. "Normal individuals use context to help categorize and remember new information."

Most people couldn't care less about the telephone book but can remember the phone numbers of family, friends, and business associates because this information means more in the context of daily life. And if you find yourself with an extra 50 cents burning a hole in your pocket, you'll remember that the price of a candy bar is within your reach, but the price of a shiny new Ferrari is light years away.

Although autism severely limits social and work skills, which depend heavily on cues taken from context and setting, it may actually improve memory tasks not dependent on context, Beversdorf found in a study published last year in Proceedings of the National Academy of Science.

People without autism asked to remember a list of words like "thread," "pin," "eye," "sewing" -- and other terms related to the word "needle" -- were more likely than autistic people to assume that "needle" was on the list, even though this "memory" was false.

With aging, more "false memory" errors pop up, which Beversdorf suggests may represent a way our brain compensates for our failing memory.

"If we can't keep track of picky details as we get older, we use contextual cues to help us remember the gist of things, although the specifics may be inaccurate," he says.

Even when you're young, your eyes and your mind may play tricks on you. Eyewitnesses who think they remember a crime may identify the wrong person from a lineup.

"We feel that we see and retain everything around us, much as a video camera records all of the details, and that with the correct cues or aids we could somehow recall everything we saw," says Daniel J. Simons, an assistant professor of psychology at Harvard University. "In reality, our memory is far less accurate than this."

In one study, Simons found that many people failed to notice when an actor they were watching in a video was replaced by a different person during a brief interruption, even though most people are confident they would notice such a change. Only about one-third of his study subjects noticed the change, even though the two actors were dressed differently.

And those were just casual observers. When you're actually trying to remember something, your ability to pay attention may be even worse.

"Under conditions of intellectual activity imposing demands on ... memory, we easily get distracted by irrelevant stimuli," says Nilli Lavie, PhD, a lecturer in psychology at University College in London.

"If you have to do something that involves paying close attention to what you see, like driving, it's a bad idea to engage in complex conversation or even deep thought," Lavie says, based on research reported in the March 2 issue of Science.

One reason why deep thought may be a distraction from attending to everyday tasks -- like the absent-minded professor who stumbles into busy traffic -- is that it may activate brain regions in a way that competes with more immediate concerns.

"Our research has focused on trying to understand how the brain accomplishes memory in the ideal situation -- in the healthy, young adult," says Randy L. Buckner, PhD, an assistant professor of psychology at Washington University in St. Louis. "We can now use that information to help us understand what kinds of changes may lead to memory difficulties such as we see in healthy aging and in dementia."

Why are learning and remembering more difficult as people get older, anyway?

One answer involves the NMDA receptor, a protein channel in the brain that helps strengthen the connection between nerve cells that happen to be active at the same time, explains Joe Z. Tsien, PhD.

For a dog to learn that a bell ringing means it's dinnertime, one group of nerve cells must respond to the sound of the ringing bell and another to the smell of food, and the two pathways must connect, explains Tsien, who is a professor of molecular biology at Princeton University in New Jersey.

"Scientists theorize that strengthening [such connections by the NDMA receptor] is the basis for learning and memory," Tsien tells WebMD. NMDA receptors in young animals tend to stay open for longer periods than in adults, which may explain why children learn more quickly than grown-ups.

In genetic experiments reported in the Nov. 10, 2000, issue of Science, Tsien's group designed mice in which the NMDA receptors in adults stayed open nearly twice as long as normal. Learning and memory capacity in these "smart mice" was much better than in normal mice.

"These experiments give us clear evidence that the NMDA receptor is a key switch of memory formation in the brain," Tsien says.

Eventually, scientists might find chemicals that improve memory in aging and in Alzheimer's disease by allowing the NMDA receptor to remain open a little longer. "Designing such drugs in humans would need to be carefully evaluated and may face many challenges," Tsien says.

In the meantime, a simpler approach to memory disorders might be to keep the mind active in a stimulating environment. Adult rats allowed to explore enriched environments containing toys, blocks, exercise wheels, and small houses do better on learning and memory performance than do rats kept in standard cages.

Tsien and colleagues reported this finding in the Nov. 7, 2000, issue of Proceedings of the National Academy of Science.

"It is possible that environmental stimulation and/or exercise can help minimize memory problems, not just those resulting from injury but also those resulting from aging," Tess L. Briones, PhD, assistant professor of medical-surgical nursing at the University of Illinois Chicago College of Nursing, tells WebMD, based on her work with animals.

Using a related approach, Richard G.M. Morris, PhD, is studying mice that are genetically modified to have one of the abnormalities seen in Alzheimer's disease. As they age, the mice develop clumps of abnormal protein, called amyloid plaques, in their brain, as do patients with Alzheimer's.

These genetically engineered mice have increasing difficulty learning new things as they get older. Their performance gets worse as the amount of amyloid plaques increases in the hippocampus, a brain structure crucial to normal memory and heavily affected by Alzheimer's disease.

Other groups are using Morris' work to determine the effect of vaccinating these mice against amyloid. "Not only do treated mice show fewer plaques, they also seem to be better at learning," Morris, a professor of neuroscience at the University of Edinburgh in Scotland, tells WebMD.