Julie Fiez CNBC Faculty Webpage	Jason Chein
Functional Magnetic Resonance Imaging Yields New Insights into the Neural Basis of Working Memory

We used functional magnetic resonance imaging to test a highly influential model of working memory proposed by Alan Baddeley and colleagues. Subjects were asked to remember five items across a 20-second delay interval. On different trials, the items were phonologically distinct words, phonologically similar words, pronounceable nonwords, or three-syllable words. The different types of stimuli were selected on the basis of prior psychological research, which has indicated that they disrupt working memory performance by differentially impairing the storage versus the rehearsal of information. The results replicated other studies in implicating the dorsolateral prefrontal, inferior parietal, left inferior frontal, supplementary motor, premotor, and cerebellar areas in performance of working memory tasks. More importantly, our study revealed differences in the pattern of activity exhibited by regions in the network. For instance, we found that a dorsal and slightly posterior region within the left inferior frontal gyrus (Broca.s area) exhibited slowly declining activation that tracked with the difficulty of each stimulus condition. In contrast, a more ventral Broca.s region exhibited sustained activation that was significantly higher in the pseudoword condition relative to the other difficult conditions. We speculated that the more dorsal region contributes to the organization and automation of a sequence of verbal items, whereas the ventral region is sensitive to sublexical phonological processes. More generally, the results call into question the common assumptions that information is maintained in a store located in temporoparietal cortex, and that the rehearsal of information is supported by a temporally constant set of processes and brain regions.

Chein JM and Fiez JA (2001). Dissociating verbal working memory system components using a delayed serial recall task. Cerebral Cortex, 11:1003-1014.