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February 17, 1997

Memory is the focus of psychologist Mary Sue Weldon's work

By Jennifer McNulty

Imagine if remembering how to walk was as hard as remembering your great uncle's birthday. If you're like most people, you'd be tripping all over yourself.

Indeed, walking is such a natural activity that it's not something people typically associate with memory. That's because it draws on what memory researchers call implicit memory, which takes no conscious effort and governs activities like walking, talking, and perceiving.

By contrast, explicit memory helps us recall things that we're deliberately trying to remember, like the birth dates of distant relatives and where we parked our car.

"We're always using memory," says associate professor of psychology Mary Sue Weldon, who has spent most of her career investigating the differences between implicit and explicit memory. The differences have implications for learning how the brain is "wired" and for understanding what happens in the brain physiologically when we remember.

The distinction between implicit and explicit memory became unmistakable about 20 years ago when researchers discovered that amnesiacs who'd suffered loss of memory were still able to perform some motor tasks like typing.

"You might ask an amnesiac if he could type, and he'd say no," explains Weldon. "But if you sat him down in front of a typewriter, he'd be able to type. That suggested that different brain processes were involved in different types of memory, and it sparked a new direction in research."

Researchers expanded their traditional work on explicit, or intentional, memory by developing empirical methods that could test unconscious memory processes as well. This growing ability to study memory has fueled debate over whether unique brain structures are dedicated to different memory functions and the degree to which different memory functions are interdependent.

One of the areas of hottest debate today is neuroimaging, specifically functional magnetic resonance imaging (fMRI), which builds on the static images used by doctors to diagnose spinal problems, knee injuries, and the like. With functional MRIs, however, brain researchers track cerebral blood flow as an indicator of brain activity.

"It's a sexy idea that is getting a lot of attention right now, but it's really a problematic approach," says Weldon, a leading figure in the field of memory research who was recently invited to author a chapter on neuroimaging in a forthcoming book to be published by Oxford University Press.

The hypothesis behind the excitement over functional MRIs is that an area of the brain "lights up" with increased blood flow when it is being used, and the expectation is that researchers will be able to document the varied blood flows that accompany different memory tasks. Ultimately, some researchers expect to isolate different areas of the brain that are used in implicit and explicit memory functions.

But Weldon is skeptical. Among the problems are the considerable lag time between how quickly neurons in the brain fire and how slowly blood flows. Moreover, it's not clear whether the brain "lighting up" indicates excitation or perhaps inhibited neural activity, says Weldon.

"It's too simple to say there are two separate memory systems," says Weldon, whose years in the laboratory have convinced her that much more complicated, interrelated processes are at work.

Rather than two independent systems that operate in isolation, Weldon suspects the answer lies in a complex interaction in which implicit memory functions support explicit memory. "I think some functions are probably spread out over multiple locations in the brain, and some locations probably control multiple functions," she says.

Weldon has recently become intrigued by the impact of aging on memory. Explicit memory skills deteriorate with age, but the implicit memory abilities of the elderly remain nearly as strong as those of young adults as long as they're not impaired by stroke or other illness, she says.

Weldon's other major area of research is collective memory, in which she investigates how groups of people develop and share memories. For example, with long-term intimate couples memory tasks tend to become specialized, with each member of the couple picking up responsibility for different areas, such as financial information, social contacts, and household management.

"That's one of the reasons it can be so difficult for the surviving partner when one dies," says Weldon. "It's like losing half your memory. It's unusual for couples to be equally involved in all areas."

Although definitive answers about many memory processes remain elusive, Weldon continues to marvel at the brain's capacity to manage information unconsciously.

"It's really remarkable that our brains are able to carry such big cognitive loads without a lot of effort on our part," says Weldon. "Can you imagine how debilitating it would be if we had to consciously think about everything our mind does?"

Go to Mary Sue Weldon's web page

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