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Head Injury Doesn't Swipe Implicit Memory

The brain can retain its ability to learn

WEDNESDAY, Jan. 23, 2002 (HealthDayNews) -- Your brain can retain at least part of its ability to learn even if a serious head trauma were to leave you temporarily comatose, a new study says.

Tests of patients with severe closed-head injuries suffered in car accidents or high falls show they preserve or only temporarily lose their ability to absorb information implicitly. That is, they can pick up on patterns yet fail to recognize that they're doing so, much the way people come to carry stereotypes without an awareness of how they've accumulated those beliefs.

If the brain is so resilient, experts say, it may be possible to leverage implicit learning in patients with head trauma to help them recover from their injury. A report on the findings appears in the January issue of Neuropsychology, a publication of the American Psychological Association.

Maureen Schmitter-Edgecombe, a psychologist at Washington State University in Pullman, led the study.

Schmitter-Edgecombe and her colleagues studied three women and 16 men who had been comatose for at least 24 hours as a result of a closed-head injury and compared them to 19 people with healthy brains. All of the people were matched for age, gender and education level.

They were asked to track the number "6" as it migrated, apparently at random, around four matrices on a computer screen. In fact, the pattern wasn't random at all, but rather set by a pre-determined rule that those being tested didn't know but could conceivably divine.

The head injury group had markedly slower response times than the healthy group. Even so, "we found that both groups' performance improved similarly across the task, and that when we changed the relationship between the pattern and the location of the '6,' both groups showed a disruption in their performance," Schmitter-Edgecombe says.

That suggests, though doesn't prove, that all the participants had the ability to learn implicitly, at least in terms of visual perception.

"We don't know exactly what they're learning, but we think it's got to be something perceptual about the stimulus," she says.

Schmitter-Edgecombe admits the number-tracking test may not measure implicit learning, and she acknowledges researchers have questioned what it shows. Still, she says, "I think our data support the idea that the participants did learn something implicitly, and I don't think this would be highly disputed. The big question that remains is what exactly did the participants learn implicitly."

What's clear, however, is that none of the participants, injured or healthy, picked up on the test's real meaning. Indeed, only one person in either group was warm.

"The fact that only two people were able to come anywhere close to what was being learned is part of the support for the fact that participants were not able to consciously express what they had learned --and hence had learned something implicitly," Schmitter-Edgecombe says.

If people with severe head injuries can retain or regain the ability to absorb new information in unconscious ways, it may be possible to use rehabilitation techniques to boost this capacity.

"If there are ways we can help them acquire new information, I think that would be wonderful," she says.

Dr. Edwin Richter, associate clinical director of the Rusk Institute of Rehabilitation Medicine in New York City and an advisor to the Brain Injury Society, says the learning ability of severe head wound patients "is still an open area for debate." But, he adds, "we do see in some cases slow or gradual learning."

Richter agrees there is "some controversy" over whether matrix tests truly measure implicit learning. If they do, he adds, "you hope that this can be generalized so that people can make use of what they're learning in other situations."

What To Do

Head injuries have been shown to increase the risk of future depression, Alzheimer's disease and other brain ailments. To find out more about head injuries and the research that's being done to help treat them, try the Brain Injury Society or the National Institutes of Health.

The Centers for Disease Control and Prevention's National Center for Injury Prevention and Control tells you why wearing a bike helmet is so important for protecting the head.

SOURCES: Interviews with Maureen Schmitter-Edgecombe, Ph.D., associate professor, psychology, Washington State University, Pullman, Wash.; Edwin Richter, M.D., associate clinical director, Rusk Institute of Rehabilitation Medicine, and associate clinical professor, rehabilitation medicine, New York University, New York City; January 2002 Neuropsychology
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