title: Evidence for multiple manipulation processes in prefrontal cortex.
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.
authors.affiliation: Department of Psychology, Rutgers University, Smith Hall, 101 Warren Street, Newark, NJ 07102, USA.
authors.forename: Dana A
authors.initials: DA
authors.lastname: Eldreth
authors.forename: Michael D
authors.initials: MD
authors.lastname: Patterson
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Porcelli
authors.forename: Bharat B
authors.initials: BB
authors.lastname: Biswal
authors.forename: Donovan
authors.initials: D
authors.lastname: Rebbechi
authors.forename: Bart
authors.initials: B
authors.lastname: Rypma
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping; D005260:Female; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D011939:Mental Recall / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D012016:Reference Values