Working memory for complex figures: An fMRI comparison of letter and fractal n-back tasks.
John Daniel Ragland, Bruce I. Turetsky, Ruben C. Gur, Faith M. Gunning‐Dixon, Travis L. Turner, Lee S. Schroeder, Robin Chan, Raquel E. Gur · Neuropsychology · 2002
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.Working memory refers to a limited capacity system responsible for temporary maintenance and online manipulation of information required for guidance of subsequent behavior.Working memory is conceptualized as having several components including a central executive system (CES) and two modality-specific slave systems: the visuospatial sketch pad and the phonological loop (Baddeley, 1986(Baddeley, , 1992;;Baddeley & Hitch, 1974).The CES allocates attentional resources and is responsible for coordination of top-down processes permitting monitoring and manipulation of information within the short-term store (e.g., temporal sequencing).The visuospatial sketch pad maintains visuospatial information in a temporary visuospatial store, and the phonological loop maintains verbal material in a phonological store through an articulatory rehearsal process.Much of the research on working memory has focused on anatomically dissociating these multiple processes.The goal of the current functional magnetic resonance imaging (fMRI) study is to use a parametric n-back paradigm (