Article Figures & Data
Figures
- Figure 1.
Experiment design. A, tDCS electrode montage. The target electrode was placed 1cm posterior to F3 (left hemisphere) or F4 (right hemisphere), located with reference to the 10–20 EEG system (Jasper, 1958). The reference electrode was placed over the contralateral orbitofrontal cortex. B, tDCS electrode montage for the control experiment. The target electrode was placed 1 cm posterior to F3 (left hemisphere) and the reference electrode was placed 1 cm posterior to F4 (right hemisphere). The reference electrode was larger than the target electrode (35 cm2). C, Standard trial outline. Participants were shown a fixation dot centrally on a monitor, followed by a stimulus (a colored circle, a symbol, or a sound depending on the experimental session), and were instructed to respond as quickly and accurately as they could to the stimulus. D, Response configurations for low and high response selection (RS) loads. Participants pressed one of eight keys to make a response, with two keys used for the low RS load blocks, and six keys used for the high RS load blocks. There were two different finger response–keyboard mapping versions, with half of the participants allocated version one and the other half version two.
- Figure 2.
Influence of training and tDCS on the high response selection load condition. A and B show the reaction times (RTs) per stimulation condition for each of the three phases of the experiment for the left and right hemisphere participants, respectively. Error bars represent the SEM of the change in RT with training. C and D show the difference in RTs between the before tDCS and the immediate post tDCS and 20 min post tDCS phases. The error bars represent SEM of the change in RT compared with the before tDCS phase [see the study by Franz and Loftus (2012) for a recent discussion on within-subjects error bars]. RTs in the sham condition for the left hemisphere reduced with practice, as did RTs for all conditions in the right hemisphere. By contrast, RTs barely reduced with training in conditions involving anodal and cathodal stimulation of the left hemisphere.
- Figure 3.
Influence of training and tDCS on the low response selection load condition. A and B show the reaction times (RTs) per stimulation condition for each of the three phases of the experiment for the left and right hemisphere participants, respectively. Error bars represent SEM of the change in RT with training. C and D show the difference in RTs between the before tDCS and the immediate post tDCS and 20 min post tDCS phases. The error bars represent the SEM of the change in RT compared with the before tDCS phase. Overall, RTs in all conditions changed little with training, and there were no differences across stimulation protocols.
- Figure 4.
Effect of left hemisphere stimulation on training in the high load condition across the three task types (A, cirlces; B, symbols; C, sounds). Graphs show the difference in reaction times (RTs) between the immediate post tDCS and 20 min post tDCS phases relative to the before tDCS phase for the left pLPFC. Error bars represent SEM of the change in RT compared with the before tDCS phase. In all three tasks RTs were reduced from before tDCS to 20 min post tDCS for the sham condition, whereas there was little change in RTs for the active stimulation conditions.
- Figure 5.
Influence of training and tDCS on response selection in the control experiment. A, Reaction times (RTs) per stimulation condition for each of the three phases of the experiment for the high response selection load condition. Error bars represent SEM of the change in RT with training. B, RTs per stimulation condition for each of the three phases of the experiment for the low response selection load condition. Error bars represent SEM of the change in RT with training. C, The difference in RTs between the before tDCS and the immediate post tDCS and 20 min post tDCS phases for the high response selection load condition. The error bars represent the SEM of the change in RT compared with the before tDCS phase. RTs in the sham condition reduced with practice. By contrast, RTs barely reduced with training in conditions involving anodal and cathodal stimulation of the left hemisphere. D, The difference in RTs between the before tDCS and the immediate post tDCS and 20 min post tDCS phases for the low response selection load condition. The error bars represent SEM of the change in RT compared with the before tDCS phase.
Tables
Left pLPFC Right pLPFC Before tDCS Immediate post tDCS 20 min post tDCS Before tDCS Immediate post tDCS 20 min post tDCS Anode High load 8.52 5.99 5.99 7.22 6.05 6.05 Low load 2.41 3.09 2.59 2.65 3.02 2.16 Cathode High load 7.59 6.67 5.93 6.67 6.23 5.93 Low load 3.46 4.26 3.27 2.84 2.35 3.52 Sham High load 10.86 7.10 5.80 5.31 5.19 5.00 Low load 2.72 1.98 1.91 3.02 3.21 2.65 The table shows the mean error rates (%) separately for each stimulation type, experimental phase, and response selection load, and for each hemisphere stimulated.
