Multitarget high-definition transcranial direct current stimulation improves response inhibition more than single-target high-definition transcranial direct current stimulation in healthy participants

Abstract

Prior studies have focused on single-target anodal transcranial direct current stimulation (tDCS) over the right inferior frontal gyrus (rIFG) or pre-supplementary motor area (pre-SMA) to improve response inhibition in healthy individuals. However, the results are contradictory and the effect of multitarget anodal stimulation over both brain regions has never been investigated. The present study aimed to investigate the behavioral and neurophysiological effects of different forms of anodal high-definition tDCS (HD-tDCS) on improving response inhibition, including HD-tDCS over the rIFG or pre-SMA and multitarget HD-tDCS over both areas. Ninety-two healthy participants were randomly assigned to receive single-session (20 min) anodal HD-tDCS over rIFG + pre-SMA, rIFG, pre-SMA, or sham stimulation. Before and immediately after tDCS intervention, participants completed a stop-signal task (SST) and a go/nogo task (GNG). Their cortical activity was recorded using functional near-infrared spectroscopy (fNIRS) during the go/nogo task. The results showed multitarget stimulation produced a significant reduction in stop-signal reaction time (SSRT) relative to baseline. The pre-to-post SSRT change was not significant for rIFG, pre-SMA, or sham stimulation. Further analyses revealed multitarget HD-tDCS significantly decreased SSRT in both the high-performance and low-performance subgroups compared with the rIFG condition which decreased SSRT only in the low-performance subgroup. Only the multitarget condition significantly improved neural efficiency as indexed by lower △oxy-Hb after stimulation. In conclusion, the present study provides important preliminary evidence that multitarget HD-tDCS is a promising avenue to improve stimulation efficacy, establishing a more effective montage to enhance response inhibition relative to the commonly used single-target stimulation.

Keywords: fNIRS; high-definition transcranial direct current stimulation (HD-tDCS); pre-supplementary motor area (pre-SMA); response inhibition; right inferior frontal gyrus (rIFG).

FIGURE 1

Schematic illustration of the study design. The experiment followed a single-blinded, randomized, between-subject, sham-controlled, and pretest-posttest design.

FIGURE 2

Simulated stimulation conditions and time progression of tDCS. (A) Simulated electric field and current flow of rIFG + pre-SMA (top), rIFG (middle), and pre-SMA (bottom). The color bar represents the field intensity and the arrow points in the direction of current flow. Column 1 is a 3D view, while column 2 to column 4 range from coronal to axial slices. (B) Schematic illustration of the duration of tDCS, ramp-up, and ramp-down periods for verum (top) and sham stimulation (bottom). The current intensity was delivered at 1.25 mA for single-target HD-tDCS, 2.5 mA for multitarget HD-tDCS, and 1.25 mA or 2.5 mA in a pseudo-random order for the sham stimulation condition.

FIGURE 3

Detailed information about procedures of behavioral tasks. (A) SST. (B) Schematic illustration of block design for GNG, a = instruction, b = cue, c = rest, d = go block, e = nogo block. (C) GNG.

FIGURE 4

fNIRS channel layout. (A) Optode arrangement, red circle = source, blue circle = detector, white square = channel. Channel 1 was located at Cz and the uppermost edge (i.e., channel 1 – 3) of the probe set overlapped with Cz-Oz. (B) Spatial registration of channels on a rendered brain. (C) Different views of optode locations.

FIGURE 5

Box and whisker plots, showing the effects of HD-tDCS on the outcome measures. (A) Behavioral performance in SST. (B) Significant interaction effects between subgroup and time for the rIFG condition (top) and sham condition (bottom) in the further analysis for SST. HP, high-performance subgroup; LP, low-performance subgroup. (C) Changes in △oxy-Hb from pretest to posttest in the pre-SMA ROI. Boxes extend from the 25 to 75th percentiles with a horizontal line representing the median. Whiskers show the min to max values. *p < 0.05, ^**p < 0.01, and ^***p < 0.001.