Evidence for Multiple Manipulation Processes in Prefrontal Cortex

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

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Included support to SUSE installation for the RPM scriptlets on template spec file, listed SUSE as a BCI−enabled distro. Revision 2007−02−08 08 Feb 2007 Revised by: avi Fixed some typos, updated Luc's page URL, added DejaVu sections, added link to FC6 Freetype RPMs, added link to Debian MS Core fonts, and added reference to the gnome−font−properties command. Revision 2006−07−02 02 Jul 2006 Revised by: avi Included link to Debian FreeType BCI package, improved the glossary with Latin1 descriptions, more clear links on the webcore fonts section, instructions on how to rebuild source RPM packages in the BCI appendix, updated the freetype recompilation appendix to cover new versions of the lib, authorship section reorganized