title: Working memory for complex figures: an fMRI comparison of letter and fractal n-back tasks.
abstract: n-back letter and fractal tasks were administered to 11 participants during functional magnetic resonance imaging to test process specificity theories of prefrontal cortex (PFC) function and assess task validity. Tasks were matched on accuracy, but fractal n-back responses were slower and more conservative. Maintenance (1-back minus 0-back) activated inferior parietal and dorsolateral PFC, with additional activation in right ventrolateral PFC during letter n-back and left lingual gyrus during fractal n-back. Maintenance plus manipulation (2-back minus 0-back) activated inferior parietal, Broca's area, insula, and dorsolateral and ventral PFC, with greater right dorsolateral PFC activation for letter n-back. Manipulation only (2-back minus 1-back) produced additional and equivalent dorsolateral PFC and anterior cingulate activation in both tasks. Results support fractal n-back validity and indicate substantial overlap in working memory functions of dorsal and ventral PFC.
authors.affiliation: Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia 19104, USA. ragland@bbl.med.upenn.edu
authors.forename: J Daniel
authors.initials: JD
authors.lastname: Ragland
authors.forename: Bruce I
authors.initials: BI
authors.lastname: Turetsky
authors.forename: Ruben C
authors.initials: RC
authors.lastname: Gur
authors.forename: Faith
authors.initials: F
authors.lastname: Gunning-Dixon
authors.forename: Travis
authors.initials: T
authors.lastname: Turner
authors.forename: Lee
authors.initials: L
authors.lastname: Schroeder
authors.forename: Robin
authors.initials: R
authors.lastname: Chan
authors.forename: Raquel E
authors.initials: RE
authors.lastname: Gur
mesh_terms: D000328:Adult; D001921:Brain / Q000033:anatomy & histology* / Q000098:blood supply; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory / Q000502:physiology*; D008875:Middle Aged; D009483:Neuropsychological Tests; D010296:Parietal Lobe / Q000033:anatomy & histology / Q000098:blood supply; D017397:Prefrontal Cortex / Q000033:anatomy & histology / Q000098:blood supply; D011897:Random Allocation; D011930:Reaction Time