Prefrontal high definition cathodal tDCS modulates executive functions only when coupled with moderate aerobic exercise in healthy persons

Abstract

Transcranial direct current stimulation (tDCS) is a promising tool to enhance cognitive performance. However, its effectiveness has not yet been unequivocally shown. Thus, here we tested whether coupling tDCS with a bout of aerobic exercise (AE) is more effective in modulating cognitive functions than tDCS or AE alone. One hundred twenty-two healthy participants were assigned to five randomized controlled crossover experiments. Two multimodal target experiments (EXP-4: anodal vs. sham tDCS during AE; EXP-5: cathodal vs. sham tDCS during AE) investigated whether anodal (a-tDCS) or cathodal tDCS (c-tDCS) applied during AE over the left dorsolateral prefrontal cortex (left DLPFC) affects executive functioning (inhibition ability). In three unimodal control experiments, the participants were either stimulated (EXP-1: anodal vs. sham tDCS, EXP-2: cathodal vs. sham tDCS) or did AE (EXP-3: AE vs. active control). Participants performed an Eriksen flanker task during ergometer cycling at moderate intensity (in EXP. 3-5). Only c-tDCS during AE had a significant adverse effect on the inhibition task, with decreased accuracy. This outcome provides preliminary evidence that c-tDCS during AE over the left DLPFC might effectively modulate inhibition performance compared to c-tDCS alone. However, more systematic research is needed in the future.

Figure 1

Results for the flanker task across experiments. Time × Condition interaction plots are displayed for the three variables reflecting Flanker test performance. The mean baseline and online values are plotted as the arithmetic mean and standard deviations. Statistical data are reported in the Result section. *asterisk displays a sig. (p < 0.05) interaction effect. AE = active control, AE = aerobic exercise. Figure drawn with GraphPad Prism version 8.2.1.

Figure 2

Exercise-related parameters RPE, HR, and Watt for EXP. 4 and EXP. 5 during the time course of the experiment. Presented are the mean values (error bar = SD) of the measuring points for BORG-RPE, heart rate, and Watt (pedal resistance) for EXP 4 (a, c, e) and 5 (b, d, f). Figure drawn with GraphPad Prism version 8.2.1.

Figure 3

Experimental design and timeline, tDCS montage, and cycle ergometer with cognitive test set-up. The upper part shows the computational model of the electric field (||E||) acting on the left DLPFC of the participants during anodal and cathodal tDCS (Neuroelectrics Instrument Controller version 2.0.10, Neuroelectrics, Barcelona, Spain). The middle part shows the experimental timeline comprising the intervention (EXP. 1: a-tDCS alone, EXP. 2: c-tDCS alone, EXP. 3: AE alone, EXP. 4: a-tDCS during (d) AE and EXP. 5: c-tDCS during AE) and control conditions (EXP 1.: s-tDCS alone, EXP. 2: s-tDCS alone, EXP. 3: Active control (AC), EXP. 4: s-tDCS during AE and EXP. 5: s-tDCS during AE). Active control (AC) was applied in all control conditions, which means that even during s-tDCS, all participants sat on the cycle ergometer and cycled with a very low intensity of 15 Watts. The lower part shows the cycle ergometer with 1) the control monitor displaying to the investigator the heart rate, pedal cadence, and Watt; 2) the task screen where the cognitive tests were presented during cycling; and 3) the response buttons (The Black Box Toolkit) fixed at the steering of the ergometer, enabling participants to easily make responses by button presses without changing posture. Cycle ergometer drawing was done using the software SketchUp.