Title

Evidence for Multiple Manipulation Processes in Prefrontal Cortex

Document Type

Article

Language

eng

Format of Original

12 p.

Publication Date

12-6-2006

Publisher

Elsevier

Source Publication

Brain Research

Source ISSN

0006-8993

Original Item ID

doi: 10.1016/j.brainres.2006.07.129; Shelves: QP376 .B72 Memorial Periodicals

Abstract

The prefrontal cortex (PFC) is known to subserve working memory (WM) processes. Brain imaging studies of WM using delayed response tasks (DRTs) have shown memory-load-dependent activation increases in dorsal prefrontal cortex (PFC) regions. These activation increases are believed to reflect manipulation of to-be-remembered information in the service of memory-consolidation. This speculation has been based on observations of similar activation increases in tasks that overtly require manipulation by instructing participants to reorder to-be-remembered list items. In this study, we tested the assumption of functional equivalence between these two types of WM tasks. Participants performed a DRT under two conditions with memory loads ranging from 3 to 6 letters. In an “item-order” condition, participants were required to remember letters in the order in which they were presented. In a “reordering” condition, participants were required to remember the letters in alphabetical order. Load-related activation increases were observed during the encoding and maintenance periods of the order maintenance condition, whereas load-related activation decreases were observed in the same periods of the reordering condition. These results suggest that (1) the neural substrates associated with long-list retention and those associated with reordering are not equivalent, (2) cognitive processes associated with long-list retention may be more closely approximated by item-order maintenance than by reordering, and (3) multiple forms of WM manipulation are dissociable on the basis of fMRI data.

Comments

Brain Research, Vol. 1123, No.1 (December 6 2006): 145-156. DOI.

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