Modulation of Working Memory and Resting-State fMRI by tDCS of the Right Frontoparietal Network

Abstract

Many cognitive functions, including working memory, are processed within large-scale brain networks. We targeted the right frontoparietal network (FPN) with one session of transcranial direct current stimulation (tDCS) in an attempt to modulate the cognitive speed of a visual working memory task (WMT) in 27 young healthy subjects using a double-blind crossover design. We further explored the neural underpinnings of induced changes by performing resting-state fMRI prior to and immediately after each stimulation session with the main focus on the interaction between a task-positive FPN and a task-negative default mode network (DMN). Twenty minutes of 2 mA anodal tDCS was superior to sham stimulation in terms of cognitive speed manipulation of a subtask with processing of objects and tools in unconventional views (i.e., the higher cognitive load subtask of the offline WMT). This result was linked to the magnitude of resting-state functional connectivity decreases between the stimulated FPN seed and DMN seeds. We provide the first evidence for the action reappraisal mechanism of object and tool processing. Modulation of cognitive speed of the task by tDCS was reflected by FPN-DMN cross-talk changes.

Figure 1

Experimental design and methods. (a) The crossover design involved two sessions with real 2 mA stimulation/sham tDCS with concurrent working memory task. Prior to and after the stimulation, participants performed a visual object matching task and underwent resting-state fMRI. (b) Offline VOMT—subjects respond whether the two consecutive objects are the same or different by pressing the YES/NO button in two difficulty levels (conventional view of objects—lower difficulty level; unconventional view of objects—higher difficulty level). (c) Online WMT—subjects view a block of faces and scenes (2 + 2, randomized order) preceded by a specific command on how to react to a probe which follows each block. Subjects respond whether the probe is consistent/inconsistent with the prior instruction by pressing the YES/NO button. (d) Montage for real and sham tDCS.

Figure 2

Seeds used for the rs-fMRI data analysis: default mode network. l/r a IPL = left/right anterior inferior parietal lobule; l/rHF = left/right hippocampal formation; vmPFC = ventromedial prefrontal cortex; PCC = posterior cingulate cortex; l/rIPL = left/right posterior inferior parietal lobule.

Figure 3

Behavioral results (a) offline VOMT (mean ± SE); (b) correlation of behavioral results online and offline tasks after tDCS (b) real and (c) sham ^∗p < 0.05.

Figure 4

Correlation of behavioral results with rMFG–DMN rs-connectivity for (a) real and (b) sham conditions.