Article Figures & Data
Figures
- Figure 1.
Simulation of current spread in the brain gray matter conducted with the NIC2 software. A, Current spread for conventional and wide HD montages. B, Electrode location according to 10/20 EEG system in the final HD montage. Central electrodes are anodal; peripheral electrodes are cathodal. C, Current spread in the final HD montage, which was used in the study.
- Figure 2.
Overview of the experimental protocol. A, Participants firstly received a stimulation and later perform a cognitive task. B, Overview of the OSPAN. Participants were required to verify mathematical equations while simultaneously memorizing a varying set of letters. Before the experimental part, participants were asked to fulfill questionnaires to check for no contraindications to tDCS and to collect sociodemographic data. After the experimental part, participants were asked to fulfill questionnaires about stimulation side effects and applied memory strategies (Extended Data Fig. 2-1).
- Figure 3.
Change of operation span metrics concerning the stimulation protocol. Black dots indicate averaged individual performance. Mixed-model ANOVA was applied to analyze the group differences. Error bars represent standard error; *p < 0.05; ***p < 0.01. A, Time of memorizing and calculation among stimulation types. B, Memory accuracy among stimulation types. C, Recall response time among stimulation types. D, Mathematical accuracy for N = 47 in each group among difficulty levels.
Tables
Data structure Type of test Power (95% C.I.) Memory accuracy (beta distribution) • Double vs single Mixed-model ANOVA, Bonferroni’s test CI: 1.712, 10.260 • Sham vs single CI: −2.924, 5.765 • Double vs sham CI: 0.221, 8.910 Mathematical accuracy (beta distribution) Double vs single
Mixed-model ANOVA, Bonferroni’s test CI: −2.316, 1.836 Sham vs single
CI: −3.674, 0.547 Double vs sham
CI: −0.787, 3.434 Time of memorizing and calculation (gamma distribution) Double vs single
Mixed-model ANOVA, Bonferroni’s test CI: −1.468, −0.544 Sham vs single
CI: −0.338, 0.586 Double vs sham
CI: −1.336, −0.428 Recall response time (gamma distribution) Double vs single
Mixed-model ANOVA, Bonferroni’s test CI: −0.960, 1.710 Sham vs single
CI: 0.877, 3.591 Double vs sham
CI: −0.502, 3.216 C.I. indicates confidence interval. Detailed information about assumption testing of mixed-model ANOVA are presented in Extended Data Table 1-1.
- Table 2.
Mean estimation of results for different types of stimulation (for trials averaged across load)
Group Double (N = 128) Single (N = 128) Sham (N = 120) Metric Mean value Standard error Mean value Standard error Mean value Standard error Memory accuracy 78.535% 1.257% 72.549% 1.257% 73.969% 1.298% Mathematical accuracy 95.045% 0.610% 95.285% 0.610% 93.722% 0.630% Time of calculation/memorizing 5.183 0.134 6.065 0.134 6.189 0.138 Time of recall 8.420 0.392 8.045 0.392 10.279 0.405 Detailed information about data distribution across groups is presented in Extended Data Table 2-1 (educational level), Table 2-2 (gender), Table 2-3 (guess about the group), and Table 2-4 (usage of mnemonics strategies).
Mean difference Standard error p value Memory accuracy Low Medium 14.240 1.449 0.0001** Low High 29.277 1.439 0.0001** Medium High 15.037 1.307 0.0001** Time of calculation/memorizing Low Medium −0.303 0.056 0.0001** Low High −0.175 0.059 0.01* Medium High 0.129 0.052 0.044* Recall response time Low Medium −4.415 0.333 0.0001** Low High −8.021 0.471 0.0001** Medium High −3.606 0.450 0.0001** Mathematical accuracy Low Medium 1.332 0.883 0.396 Low High 3.111 0.824 0.001** Medium High 1.779 0.727 0.045*
Figure 2-1
Translated versions of questionnaires about tDCS contraindications, stimulation side effects and applied memory strategies. Participants fulfilled the contraindication questionnaire along with the consent form signing before the HD-tDCS setup. The TES side effects and memory strategies questionnaires were delivered to participant immediately after they finished the Operation Span task. Download Figure 2-1, DOCX file.
Table 1-1.
Testing the data on ANOVA assumptions of sphericity and homogeneity. Download Table 1-1., DOCX file.
Table 2-1.
Contingency matrix for the distribution of education level categories across three stimulation groups. Download Table 2-1., DOCX file.
Table 2-2.
Contingency matrix for the distribution of gender across three stimulation groups. Download Table 2-2., DOCX file.
Table 2-3.
Contingency matrix for the distribution of participants who correctly guessed their group assignment. Download Table 2-3., DOCX file.
Table 2-4.
Contingency matrixes for the distribution of participants who applied memory strategies such as Mnemonics, Merging letters into word, Articulation of the letters, Imagination of a scene. Download Table 2-4., DOCX file.
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