N-back working memory paradigm: a meta-analysis of normative functional neuroimaging studies

Abstract

One of the most popular experimental paradigms for functional neuroimaging studies of working memory has been the n-back task, in which subjects are asked to monitor the identity or location of a series of verbal or nonverbal stimuli and to indicate when the currently presented stimulus is the same as the one presented n trials previously. We conducted a quantitative meta-analysis of 668 sets of activation coordinates in Talairach space reported in 24 primary studies of n-back task variants manipulating process (location vs. identity monitoring) and content (verbal or nonverbal) of working memory. We found the following cortical regions were activated robustly (voxelwise false discovery rate = 1%): lateral premotor cortex; dorsal cingulate and medial premotor cortex; dorsolateral and ventrolateral prefrontal cortex; frontal poles; and medial and lateral posterior parietal cortex. Subsidiary meta-analyses based on appropriate subsets of the primary data demonstrated broadly similar activation patterns for identity monitoring of verbal stimuli and both location and identity monitoring of nonverbal stimuli. There was also some evidence for distinct frontoparietal activation patterns in response to different task variants. The functional specializations of each of the major cortical components in the generic large-scale frontoparietal system are discussed. We conclude that quantitative meta-analysis can be a powerful tool for combining results of multiple primary studies reported in Talairach space. Here, it provides evidence both for broadly consistent activation of frontal and parietal cortical regions by various versions of the n-back working memory paradigm, and for process- and content-specific frontoparietal activation by working memory.

Figure 1

Meta‐analytic activation maps for all n‐back studies (top panel) and for three n‐back variants: verbal identity monitoring, nonverbal identity monitoring, and nonverbal location monitoring. Regions consistently activated across studies are color‐coded according to the probability of false discovery (voxelwise P < 0.01; FDR corrected). The right side of each section represents the right side of the brain; the z‐coordinate in Talairach space is indicated below each section. Regions of activation highlighted by these selected slices include lateral and medial premotor cortex (z = 52, 40), lateral and medial posterior parietal cortex (z = 52, 40), dorsolateral (z = 28) and ventrolateral (z = 4) prefrontal cortex and frontal poles (z = 4). For more anatomical details see Table II.

Figure 2

Meta‐analytic differential activation maps comparing verbal vs. nonverbal identity‐monitoring studies (top panel) and nonverbal location monitoring vs. nonverbal identity monitoring (bottom panel). Regions differentially activated between groups of studies are color‐coded according to the probability of false discovery (voxelwise P < 0.01; FDR corrected). The right side of each section represents the right side of the brain; the z‐coordinate in Talairach space is indicated below each section.