ANN ARBOR—A new analysis of the human brain at work, to be published in the March 12 issue of Science, elucidates how the frontal lobes are organized, providing strong evidence that verbal and spatial memories are processed in different hemispheres.

The analysis, by University of Michigan psychologists Edward E. Smith and John Jonides, focuses on working memory, a mental system that includes both the temporary storage of verbal, spatial and object information, and various “executive processes” for using that information. Among the processes are everyday mental activities such as paying attention to one source of information but not another as a way of dealing with conflicting information.

“How the frontal cortex is organized is a question of tremendous interest,” says Smith, the Arthur W. Melton Collegiate Professor of

Psychology and a research scientist at both the U-M Mental Health Research Institute and the U-M Institute for Social Research. “Our analysis suggests that it is partly organized by the type of information being processed, and partly by the type of operation being performed—either storage or active manipulation of the stored information.”

Verbal storage tasks activate left-hemisphere speech areas, Smith and Jonides found, while spatial storage tasks activate specific areas of the right cortex, and storage of information about objects, such as smiling vs. frowning faces, activates still different, more ventral, or lower, regions at the front of the cortex.

Smith and Jonides also found that two of the fundamental executive processes—paying attention to one source of information rather than another, and switching from one task to another—activate specific regions at the front of the brain: the anterior cingulate and the dorsolateral prefrontal cortex.

Their analysis is based on brain imaging experiments, done at the U-M and elsewhere,

using PET (positron emission tomography) and functional MRI (magnetic

resonance imaging) scans. The images were made while subjects were actively

engaged in a variety of mental tasks including an experimental task

designed to isolate a specific memory process and a control task that

differed from the experimental task only in that it did not involve

the memory process.

Long thought to be the seat of higher mental functions such as planning and problem solving, the frontal cortex comprises one-third of the human brain, a proportion much larger than in other primates, Smith notes.

“Damage to the prefrontal cortex is common in accident victims,” he says. “They have trouble concentrating on some things while ignoring others, or switching from one task to another. These are the kinds of activities involved in the executive functions that we’re studying.”

In accident or stroke victims with damage to specific regions of the frontal lobes, a more precise understanding of how various regions of the frontal cortex are involved in specific mental activities should allow health care professionals to devise more effective compensatory therapies, according to Smith. “If you know that an area involved in processing short-term memory for spatial information has been damaged,” he says, “you can work on developing more elaborate verbal presentations of the information, to help people process the same information using a different modality.”

Major funding for the study was provided by the U.S. Office of Naval Research, the National Institute on Aging, and the McDonnell-Pew Program in Cognitive Neuroscience.

U.S. Office of Naval Research