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Eye-Opening Brain Study on Memory |
| By
Kimyette Finley |
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Jan 29, 2002 |
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| Dr. Stephen Christman |
If you can’t remember something, try moving your eyes left to right rapidly for 30 seconds — especially if you’re right-handed.
“We’ve been working on a way to temporarily turn a right-hander’s brain into a left-hander’s,” said Dr. Stephen Christman, professor of psychology.
Last year, he and former UT graduate student Ruth Propper (now at Merrimack College) received international recognition when their research was published in the journal Neuropsychology. Their findings indicated that people who are left-handed or have immediate left-handed family members have stronger episodic memory — recall and recognition of events — in contrast to general world knowledge — semantic memory.
“Everybody can remember that Mount Everest is the tallest mountain on Earth. Left-handers may be a little more likely to remember where and when they learned it,” Christman said.
The UT professor estimated between 60 to 70 percent of the population is born strongly right-handed, with no left-handers in their family. The other 30 to 40 percent is essentially born with random handedness, with about half of those becoming left-handed.
According to Christman, the corpus callosum, which starts to mature in most people around age 4 or 5, is larger in left-handers. The two hemispheres in the corpus callosum begin to interact, and myelin sheathing (insulation) also occurs. Myelin sheathing allows for more efficient communication between neurons.
About five years ago, Endel Tulving, a University of Toronto researcher, found that when people are dealing with episodic memories, both sides of the brain light up and become more active. When people were recalling world knowledge or general facts, only the left side of the brain would light up.
“This suggested to us that there may be handedness differences in memory, since the two hemispheres are more prone to interact in left-handers than right-handers. We’ve shown that with a number of low-level perceptual and motor-type tasks,” Christman said. His research team studied right-handers who had familial left-handedness.
Christman’s wife, a clinical therapist, brought home a therapy magazine featuring Eye Movement Desensitization and Reprocessing (EMDR). This is an eye task used to treat posttraumatic stress patients who have difficulty remembering the specifics of their traumas. A researcher found if she had her patients move their eyes left to right for about 30 seconds while they were trying to remember the traumatic event, the memory would vividly come flooding back.
Armed with that information and research from the left-hand and right-hand studies, Christman and Kilian Garvey, a fourth-year doctoral candidate in cognitive neuropsychology, conducted a study assessing EMDR techniques in remembering basic information. “When you move your eyes to the left, you activate the right side of your brain. If you move your eyes to the right, your left hemisphere lights up. Our hemispheres are asymmetrically activated; one’s always a little more activated than the other,” Christman explained.
“We were interested in the eye movements because it increases communication between hemispheres,” said Garvey, who used the study as his master’s thesis work. In turn, the interaction between the hemispheres helps episodic memory.
A study was conducted last year at UT and included 280 participants. “It was the biggest study we’ve ever done,” Christman said. Participants were asked to study a series of words. The control group studied the words and waited half an hour and then took the memory test with no other manipulations. Different tests were used to tap into episodic versus semantic memory. Episodic memory was tested by asking people to recognize words they had seen at the beginning of the experiment. Semantic memory was tested by asking people to complete word fragments.
“Our experimental groups, right before they took the memory tests, they engaged in various types of eye movements. We looked at two different dimensions of eye movement. We had people either move their eyes left-right or up-down. Left-right will activate the two hemispheres; up-down won’t. We were predicting that only left-right movement should help the memory,” Christman explained.
Two types of eye movements were compared. Saccadic eye movements are fast and jerky; pursuit eye movement features a slower eye movement when tracking a moving object. According to Christman, saccadic eye movements are generated in the cortex and are strongly driven by consciousness.
“Our prediction was that it should require horizontal saccadic eye movements to activate the two hemispheres more. It’s a complicated design but the results are wonderful,” Christman said. “Left-right saccadic eye movements, but not up-down or smooth pursuit, produced a significant improvements in episodic memory. Eye movements in general had no effects on semantic memory.”
Previous studies indicated that left-handedness is associated with better episodic memory, and the current data shows that eye movements helped the right-handers in the study catch up with and perform at the same level as left-handers.
“Our results clearly indicate that these eye movements are helping because the memory is episodic and autobiographical. Whether you’re trying to remember a horrific experience or trying to remember a word you saw in your autobiographical memory, the eye movements help both,” Christman said.
Christman said the research doesn’t indicate how long the increased interhemispheric interaction and improved memory caused by the eye movements lasts, and there’s still a question if the eye movements will help with memory encoding. However, the results do indicate the eye exercises can help with memory retrieval.
The UT professor plans to submit the findings to the flagship journal of the American Psychological Society, Psychological Science, this month.
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