May 28, 1998 St. Louis, May 22, 1998 -- If you see a gunman fleeing from a bank, how do you remember the bank's name and the gunman's face?
A new study shows that when you're told to remember a word, you activate a region on the left side of your brain. When you're told to remember an unfamiliar face -- something to which you can't attach a name -- you activate a region on the right. Interestingly, both regions become active when you're asked to remember an object, such as a gun, that has a name.
"So the left side seems to be active when you're using verbal codes, which you use for either words or namable objects. The right side seems to be active when you're using nonverbal codes, such as visual features of unfamiliar faces or namable objects," says Steven E. Petersen, Ph.D., professor of neurology, neurobiology and radiology at Washington University School of Medicine in St. Louis. Petersen heads the research team that performed the study. Graduate student William M. Kelley is first author of a paper in the May 22 issue of Neuron that reports the results.
There are three stages of memory. First, you take information into the system and make it available for memory as if you were editing a document on your computer screen. Memory researchers call this process encoding. The second stage is storage, where you make a long-lasting change in the brain, saving the document to your hard drive. The third stage is retrieval, where you get the document back on the screen.
The researchers were addressing a long-standing debate about encoding. Psychologists studying patients with brain damage have concluded that people use the left side of the brain for language tasks and the right side for handling spatial and pictorial information. But scientists who make images of the brain at work have concluded that the left side is used for memorization and the right for retrieval.
Petersen noticed, however, that most of these images were made while subjects were memorizing words or sentences. He therefore designed a study to test the effects of nonverbal information.
Using functional magnetic resonance imaging (fMRI), Kelley and colleagues performed two experiments. In the first, they imaged five subjects who were asked to memorize written words, line drawings of objects such as frogs and ladders, and pictures of faces they would be unable to name. Subsequent testing showed they remembered these words, namable objects and unfamiliar faces very well, though they did best with namable objects.
In a second experiment, five different subjects were asked to memorize the test images. At a later time, they were asked to just look at them.
All of the subjects activated a region in the upper part of the left frontal lobe when they were memorizing words. If you put your finger on top of your head, and move it to the front between your left ear and your hair's midline, you will be near that region. The region activated by the unfamiliar faces was in a corresponding position on the right side of the brain. "This is the most clear-cut finding I've ever seen in an imaging study," Petersen says.
"The main conclusion from this study is that regions in the frontal lobe can be affected by the type of material you are trying to memorize," Kelley says. "But an interesting tidbit is that performance was best with namable objects, which activated both sides of the brain. So in a sense, two sides are better than one. If you use both sides, you're more likely to remember an object later."
The second experiment showed that the frontal lobes are affected by instructions that people receive. These brain regions become much more active when people are told to memorize information than when they are told to just look.
While this study focused on the normal brain, Petersen speculates that the results might be useful to patients with stroke or head injury. "If you get a lesion in the left frontal lobe, you might be better off developing a nonverbal strategy for remembering things," he says. "If the lesion is on the right, you might want to try a verbal strategy."
Kelley WM, Miezin FM, McDermott KB, Buckner RL, Raichle ME, Cohen NJ, Ollinger JM, Akbudak E, Conturo TE, Snyder AZ, Petersen SE. Hemispheric specialization in human dorsal frontal cortex and medial temporal lobe for verbal and nonverbal memory encoding. Neuron 20, 927-936, May 22, 1998.
Grants from the National Institutes of Health, the Charles A. Dana Foundation and the McDonnell Center for Higher Brain Function supported this research.
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