Where in the brain is working memory?

Working memory holds and relates a variety of stored information during tasks such as talking, reading, and recognizing objects. The dominant theory of working memory divides the labor into executive control, which coordinates brain activities, and active maintenance, which acts as a holding bin for data. These two functions have been thought to occupy separate regions of the brain.

Two studies in the April 10 Nature used functional magnetic resonance imaging to take second-by-second pictures of the brain during simple memory tasks. These brain scans reveal that executive control and active maintenance aren't entirely distinct.

In one study, volunteers viewed a face on a computer monitor for 3 seconds, tried to keep it in mind during an 8-second pause, then viewed another face. If the faces matched, the volunteers pressed a button.

The scans showed that areas at the back of the brain lit up briefly when the faces first appeared and that frontal areas became and stayed active during the pause. That distinction wasn't complete, however. Some rear areas lit up slightly during the pause, while some frontal areas responded slightly when the faces appeared.

The results demonstrate that perception and memory require the coordinated efforts of different parts of the brain, says Susan M. Courtney, who conducted the study with colleagues from the Laboratory of Brain and Cognition at the National Institutes of Health in Bethesda, Md.

In the second study, scientists scanned volunteers' brains as they tried to recall increasingly long sequences of consonants flashed on a screen. The volunteers were also asked to say whether the letters had appeared in previous sequences. As the string of letters lengthened, activity in frontal areas of the brain increased; other areas of the brain also lit up.

Like the results of the first study, these challenge the theory that one part of the brain coordinates information processing while another part keeps the information available, says Jonathan D. Cohen of Carnegie Mellon University and the University of Pittsburgh, who led the investigation. Cohen theorizes that several parts of the brain work together to hold and coordinate information.

Courtney and Cohen agree that imaging brain activity from millisecond to millisecond in the future could improve scientists' understanding of working memory.

Patricia Goldman-Rakic, a neurobiologist at Yale University School of Medicine, notes in a commentary accompanying the reports that although activity in the front of the brain increased in each study as memory tasks grew longer and more complex, different frontal areas of the brain were activated. Therefore, the type of information being processed dictates where memory will be located at any given time. "It's not just one spot in the brain."