The Neuronal Correlates of Digits Backward Are Revealed by Voxel-Based Morphometry and Resting-State Functional Connectivity Analyses

Rui Li,Chunshui Yu,Yunting Zhang,Tianzi Jiang,Wen Qin,Dante R Chialvo

doi:10.1371/journal.pone.0031877

Abstract

Digits backward (DB) is a widely used neuropsychological measure that is believed to be a simple and effective index of the capacity of the verbal working memory. However, its neural correlates remain elusive. The aim of this study is to investigate the neural correlates of DB in 299 healthy young adults by combining voxel-based morphometry (VBM) and resting-state functional connectivity (rsFC) analyses. The VBM analysis showed positive correlations between the DB scores and the gray matter volumes in the right anterior superior temporal gyrus (STG), the right posterior STG, the left inferior frontal gyrus and the left Rolandic operculum, which are four critical areas in the auditory phonological loop of the verbal working memory. Voxel-based correlation analysis was then performed between the positive rsFCs of these four clusters and the DB scores. We found that the DB scores were positively correlated with the rsFCs within the salience network (SN), that is, between the right anterior STG, the dorsal anterior cingulate cortex and the right fronto-insular cortex. We also found that the DB scores were negatively correlated with the rsFC within an anti-correlation network of the SN, between the right posterior STG and the left posterior insula. Our findings suggest that DB performance is related to the structural and functional organizations of the brain areas that are involved in the auditory phonological loop and the SN.

Highlights

Working memory (WM) refers to a limited system that provides for the temporary storage and manipulation of the information necessary for complex cognitive tasks and that provides an interface between perception, long-term memory and action [1,2]
Many previous studies on brain disorders have revealed that brain areas with changes in the gray matter volume (GMV) are commonly accompanied by altered resting-state functional connectivity (rsFC) between these regions and other related brain areas [22,23,24]. The hippocampus had both a reduced GMV [25] and rsFCs in patients with Alzheimer disease [26]. These findings suggest that structural (i.e., GMV) change in a brain area may be associated with rsFC alteration in this area and that the combination of voxel-based morphometry (VBM) and rsFC analyses can improve our understanding of the pathology of brain diseases
We found that the verbal-digital WM capacity was positively correlated with the GMVs of the right anterior superior temporal gyrus (STG), suggesting that the accurate perception of auditory input is important for the capacity of the verbal WM

Summary

Introduction

Working memory (WM) refers to a limited system that provides for the temporary storage and manipulation of the information necessary for complex cognitive tasks and that provides an interface between perception, long-term memory and action [1,2]. A widely accepted model of WM has proposed that it consists of four subsystems, including the central executive system, the phonological loop, the visuospatial sketchpad, and the episodic buffer [1,2,4,5,6]. The central executive system is an attentional control system that is responsible for strategy selection and for the regulation and coordination of the various processes involved in the phonological loop and the visuospatial sketchpad [2,6]. The episodic buffer is assumed to be a limited-capacity system that depends heavily on executive processing but that differs from the central executive system in being principally concerned with the storage of information rather than with attentional control. The episodic buffer is capable of binding information from different modalities into a single multi-faceted code [7]

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