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

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

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

Contributed by Edward E. Smith

Abstract

We studied the performance of young and senior subjects on a well known working memory task, the Operation Span. This is a dual-task in which subjects perform a memory task while simultaneously verifying simple equations. Positron-emission tomography scans were taken during performance. Both young and senior subjects demonstrated a cost in accuracy and latency in the Operation Span compared with performing each component task alone (math verification or memory only). Senior subjects were disproportionately impaired relative to young subjects on the dual-task. When brain activation was examined for senior subjects, we found regions in prefrontal cortex that were active in the dual-task, but not in the component tasks. Similar results were obtained for young subjects who performed relatively poorly on the dual-task; however, for young subjects who performed relatively well in the dual-task, we found no prefrontal regions that were active only in the dual-task. Results are discussed as they relate to the executive component of task switching.

Footnotes

↵ † To whom reprint requests should be addressed at: Department of Psychology, 525 East University Avenue, Ann Arbor, MI 48109-1109. E-mail: eesmith{at}umich.edu.
↵ § Most WM tasks that have been used in neuroimaging studies do not require this processing–storage cycle. Many of these studies have used item-recognition tasks in which participants merely have to decide whether a probe item is part of a previously memorized set; there is no sequential updating of WM, no maintenance of a WM load while processing other material, and no switching between tasks. Another widely used task is the n-back paradigm. Participants are presented a sequence of items and for each one must decide whether it matches the one presented n back (e.g., 2 or 3 back) in the sequence. 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].
↵ ¶ On Memory accuracy, the good-young showed a 4% decline between the single- vs. dual-task. In contrast, the poor-young showed a 17% decline. This task × group interaction was significant (P < 0.005).
Abbreviations:

WM,

working memory;

PET,

positron-emission tomography;

PFC,

prefrontal cortex;

ROIs,

regions-of-interest