Components of verbal working memory: Evidence from neuroimaging

Components of verbal working memory: Evidence from neuroimaging

^*Department of Psychology, and ^‡Division of Nuclear Medicine, University of Michigan, Ann Arbor, MI 48109-1109

Abstract

We review research on the neural bases of verbal working memory, focusing on human neuroimaging studies. We first consider experiments that indicate that verbal working memory is composed of multiple components. One component involves the subvocal rehearsal of phonological information and is neurally implemented by left-hemisphere speech areas, including Broca’s area, the premotor area, and the supplementary motor area. Other components of verbal working memory may be devoted to pure storage and to executive processing of the contents of memory. These studies rest on a subtraction logic, in which two tasks are imaged, differing only in that one task presumably has an extra process, and the difference image is taken to reflect that process. We then review studies that show that the previous results can be obtained with experimental methods other than subtraction. We focus on the method of parametric variation, in which a parameter that presumably reflects a single process is varied. In the last section, we consider the distinction between working memory tasks that require only storage of information vs. those that require that the stored items be processed in some way. These experiments provide some support for the hypothesis that, when a task requires processing the contents of working memory, the dorsolateral prefrontal cortex is disproportionately activated.

Footnotes

↵ † To whom reprint requests should be addressed at: Department of Psychology, University of Michigan, 525 East University, Ann Arbor, MI 48109-1109. e-mail: eesmith{at}umich.edu.
This paper was presented at a colloquium entitled “Neuroimaging of Human Brain Function,” organized by Michael Posner and Marcus E. Raichle, held May 29–31, 1997, sponsored by the National Academy of Sciences at the Arnold and Mabel Beckman Center in Irvine, CA.
↵ § Note further that this task also may involve some inhibition because of the inclusion of “foils,” e.g., cases in which X occurred not preceded by A.
ABBREVIATIONS:

WM,

working memory;

PET,

positron emission tomography;

fMRI,

functional magnetic resonance imaging;

DLPFC,

dorsolateral prefrontal cortex;

BA,

Broadmann area