Working memory for complex figures: An fMRI comparison of letter and fractal n-back tasks.

Abstract

Abstractn -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, , 1992Baddeley & 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 (Awh et al., 1996;Braver et al., 1997;Cohen et al., 1994Cohen et al., , 1997Gervins & Cutillo, 1993; to contrast the effect of working memory load on regional brain function during a standard letter n-back task versus an nback task using complex geometric objects that have not been previously studied. NIH Public Access Author ManuscriptNeuropsychology. Author manuscript; available in PMC 2015 February 18. Published in final edited form as:Neuropsychology. 2002 July ; 16(3): 370-379. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptDemonstrating similar effects of working memory load on the two tasks provides initial evidence for the construct validity of the new task.The process specificity model attempts to parse prefrontal regions mediating different components of working memory. According to the model, ventrolateral prefrontal cortex (PFC; Brodmann's area [BA] 44, 45, and 47) is responsible for maintenance of information in the visuospatial and phonolog...

Continuous ASL perfusion fMRI investigation of higher cognition: Quantification of tonic CBF changes during sustained attention and working memory tasks

“…Then, we made a list of activated regions from those studies to compare them with the activated areas of the present study. It was found that every activated area found in our study (Table 2) was also reported as a significant activation focus in one or more previous studies of the verbal 2-back task (Awh et al, 1996;Braver et al, 1997;Cohen et al, 1994Cohen et al, , 1997Honey et al, 2000;Jonides et al, 1997;Kim et al, 2002;Nystrom et al, 2000;Ragland et al, 2002;Smith et al, 1996;Veltman et al, 2003).…”

A rapid fMRI task battery for mapping of visual, motor, cognitive, and emotional function

“…It is known to activate eloquent areas (Broca's and Wernicke's) of speech planning and execution in the dominant, and sometimes non-dominant, hemisphere. The n-back task is a widely-used paradigm (Ragland, et al 2002;Marshall, et al 2004) in studies of working memory brain circuitry, and has been shown to activate a number of areas in the frontal and parietal cortices, in particular the dorsolateralprefrontal cortex (DLPFC). In our implementation of this task a series of letters was displayed one in a time, and subjects were asked to determine if the current letter was the same as that presented two letters previously (2-back).…”

Functionally-Detected Cognitive Impairment in High School Football Players without Clinically-Diagnosed Concussion

“…In each run subjects performed one block (15 presentations, 3-sec interval, 5 targets per block) each of 0-, 1-, and 2-back tasks for single letters. 30,31 Visual presentation was via fiber-optic goggles (NordicNeuroLab, Bergen, Norway). Subjects responded by dominant index finger via fiberoptic button box (Current Designs, Philadelphia, PA).…”