Remember the future II: meta-analyses and functional overlap of working memory and delay discounting

Abstract

Previously we showed that working memory training decreased the discounting of future rewards in stimulant addicts without affecting a go/no-go task. While a relationship between delay discounting and working memory is consistent with other studies, the unique brain regions of plausible causality between these two abilities have yet to be determined. Activation likelihood estimation meta-analyses were performed on foci from studies of delay discounting (DD = 449), working memory (WM = 452), finger tapping (finger tapping = 450), and response inhibition (RI = 450). Activity maps from relatively less (finger tapping) and more (RI) demanding executive tasks were contrasted with maps of DD and WM. Overlap analysis identified unique functional coincidence between DD and WM. The anterior cingulate cortex was engaged by all tasks. Finger tapping largely engaged motor-related brain areas. In addition to motor-related areas, RI engaged frontal brain regions. The right lateral prefrontal cortex was engaged by RI, DD, and WM and was contrasted out of overlap maps. A functional cluster in the posterior portion of the left lateral prefrontal cortex emerged as the largest location of unique overlap between DD and WM. A portion of the left lateral prefrontal cortex is a unique location where delay discounting and working memory processes overlap in the brain. This area, therefore, represents a therapeutic target for improving behaviors that rely on the integration of the recent past with the foreseeable future.

Keywords: Activation likelihood estimation (ALE); delay discounting; dorsal lateral prefrontal cortex (DLPFC); fMRI; temporal discounting; working memory.

Copyright © 2014 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Significant FDR corrected (p<.05) ALE values for tasks of (A) delay discounting (B) working memory (C) finger tapping and (D) response inhibition. ALE values for left (L) and right (R) hemispheres are presented on the MNI standard space template.

Figure 2

Significant FDR corrected (p<.05) results showing activity for delay discounting and working memory contrasted with that of finger tapping (A,B) and response inhibition (C,D). Z-score values for left (L) and right (R) hemispheres are presented on the MNI standard space template.

Figure 3

Combined and individual overlaps in activity maps of delay discounting (DD) and working memory (WM), contrasted with finger tapping (FT) and response inhibition (RI). Maps show activity in the left (L) and right (R) hemispheres for (A) delay discounting (yellow), working memory (blue) as well as functional overlap between the two tasks (green). (B) Exclusive functional overlaps of DD and WM.

Figure 4

Location of exclusive functional overlaps. Figure shows overlaps of delay discounting (DD) and working memory (WM) activity from Fig. 3b projected on three-dimensional infinite-depth MNI anatomical templates (i.e., glass brains). (A) Functional overlaps on brain marking the left (L) hemisphere locations of the superior frontal gyrus (SFG), middle frontal gyrus (MFG) and inferior frontal gyrus (IFG). Sulci are the superior frontal sulcus (sfs), superior precentral sulcus (spcs), central sulcus (cs), inferior frontal sulcus (ifs), inferior precentral sulcus (ipcs) and lateral sulcus (ls). (B) Functional overlaps on brain showing relevant Brodmann Area locations. (C) Functional overlaps projected on MNI whole head template.