A resource model of the neural basis of executive working memory

Abstract

Working memory (WM) refers to the temporary storage and processing of goal-relevant information. WM is thought to include domain-specific short-term memory stores and executive processes, such as coordination, that operate on the contents of WM. To examine the neural substrates of coordination, we acquired functional magnetic resonance imaging data while subjects performed a WM span test designed specifically to measure executive WM. Subjects performed two tasks (sentence reading and shortterm memory for five words) either separately or concurrently. Dual-task performance activated frontal-lobe areas to a greater extent than performance of either task in isolation, but no new area was activated beyond those activated by either component task. These findings support a resource theory of WM executive processes in the frontal lobes.T he process whereby information is temporarily maintained in memory for use in ongoing mental operations is referred to as working memory (WM). The WM system is thought to consist of verbal and spatial short-term stores and executive processes that operate on the contents of these stores (1-3). Executive WM processes such as multiple task coordination, set shifting, interference resolution, and memory updating are thought to be essential for high-level thought processes and to be subserved by prefrontal cortex (PFC) (2-6). Executive WM is likely to be comprised of a number of distinct processes, and functional neuroimaging may be useful in dissociating those processes to the extent that these processes rely on distinct neural substrates (7-18). The present experiments focus on the neural substrates of dual-task coordination during the concurrent performance of two tasks.Psychologists have developed test paradigms with the goal of measuring executive WM capacity. These WM span tests, which include reading span (19)(20), listening span (21), operation span (22), and counting span (23), share the common property that they require concurrent processing (such as reading sentences for comprehension) and short-term maintenance (such as remembering the last word in each sentence). Unlike single-task short-term memory measures such as digit span or word span, WM span tests are powerful predictors of performance on a wide variety of verbal (e.g., verbal Scholastic Aptitude Test, text comprehension) and nonverbal measures (e.g., mathematical and reasoning problems) (19)(20)(24)(25)(26)(27)(28). WM span tests are also sensitive to changes in cognitive ability throughout development (23, 29) and in old age (26), as well as in neurological diseases that compromise frontal-lobe functioning (30, 31). WM span tests yield a psychometrically robust measure of executive WM capacity, but the neural substrates of performance of such a task have not been yet been thoroughly explored (32).In the present experiments, we used functional magnetic resonance imaging to measure brain activity associated with performance of a WM span test. Performing two tasks concurrently instead of one requires additional mental re...

The neural basis of task-switching in working memory: Effects of performance and aging

“…There are posterior activations in this critical contrast; but presumably they reflect the fact that the Math activations are not fully subtracted out, because it is an average of Math Plus Memory that is subtracted from Operation Span. The null findings about the PFC are consistent with the negative results of Bunge et al (7). The critical results are different for the poor-young subjects.…”

“…Analyses of variance for math accuracy and memory accuracy show main effects of performance on the single-vs. the dual-task, but no effect of age and no interaction between task and age. is that our version of the Operation Span is indeed more demanding than the constituent tasks [recall this was less the case in the Bunge et al (7) study], and that our parametric changes were successful in equating accuracy levels for senior and young subjects.…”

“…This task does require sequential updating of WM, but it does not require maintaining a WM load while doing a different kind of processing, and it does not necessitate switching between tasks. A similar story holds for many other WM neuroimaging paradigms [an exception is that used by Bunge et al (7), which we will soon discuss].…”

“…In one of the only prior studies that used a WM task that required a process-storage cycle, Bunge et al (7) imaged subjects while they performed tasks similar in structure to the Operation Span. (The dual-task of Bunge et al's experiment required evaluating sentences and remembering the sentence-final word, whereas their other tasks required just sentence evaluation, or just memory for words.)…”

Integration of emotion and cognition in the lateral prefrontal cortex

“…Lateral PFC activity in the current paradigm appears to reflect psychological load: how much top-down support is needed to maintain behavioral performance at a given set point (32,47).…”