The brain's memory helpers.

Individuals routinely call to mind memories of events they have experienced, but scientists are just beginning to understand how the brain makes this possible. A new study suggests that separate brain systems store and recall incidents in one's life; moreover, each of these systems relies on its own helper areas that specialize in what happened, where it occurred, or when it took place.

The findings, published in the Oct. 1 Proceedings of the National Academy of Sciences, support earlier evidence that the left side of the prefrontal cortex always participates in the acquisition of novel information, whereas the right prefrontal cortex consistently aids in remembering that material later on (SN: 7/6/96, p. 5). Each prefrontal area belongs to a general memory network that receives dispatches from hard-bitten neural correspondents interested only in the contents, location, or time of various events, assert psychologist Lars Nyberg of Umea University in Sweden and his colleagues.

Twelve volunteers age 19 to 40 completed trials in which they read two series of words presented individually on a computer screen. Words appeared randomly on the left and right sides of the screen. Positron emission tomography (PET) scans were taken during three pairs of tasks: Participants studied the words and later tried to pick them out of a longer list; they memorized the left or right placement of words and later attempted to remember those positionings; and they studied which words appeared in the first and second series and later tried to divvy words into the correct lists.

Increased blood flow, signifying greater brain activity, appeared in the left prefrontal cortex during the three learning trials and in the right prefrontal cortex during the three memory trials. Each task also boosted activity in specific cerebral spots. For instance, the learning of word locations was accompanied by blood-flow surges in right brain tissue toward the back of the head, an area that has been implicated in the coordination of spatial knowledge.

"It's exciting that scientists are starting to locate brain areas involved in specific aspects of event memories," remarks neuroscientist Randy L. Buckner of the Massachusetts General Hospital-Nuclear Magnetic Resonance Center in Charlestown. "We'll be seeing much more of this type of research."