Behavioral entrainment to rhythmic auditory stimulation can be modulated by tACS depending on the electrical stimulation field properties
- Max Planck Institute for Empirical Aesthetics, Germany
- Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Denmark
- Section for Magnetic Resonance, DTU Health Tech, Technical University of Denmark, Denmark
- Toronto Metropolitan University, Canada
Figures
Figure 1
Auditory stimulus and tACS optimization pipeline.
(a) Stimulus representation. A complex noise stimulus is frequency modulated at 2 Hz without any rhythmic modulation of its amplitude. Silent gaps are presented at different phase locations of the FM-stimulus modulation cycle. (b) Group data showing the regions exhibiting higher BOLD signal during the FM-stimulus presentation compared to the implicit baseline, p(FWE)<0.05. Graphs in the center show the beta estimates extracted for the whole cluster for each participant per hemisphere. Box plots show median (horizontal dashed lines), mean (black cross), 25th and 75th percentiles (box edges) and extreme datapoints not considered outliers (+/–2.7σ and 99.3 percentiles, whiskers). Each circle represents a single participant, N = 39. (c) Overlap of single-participant binary masks after thresholding the individual t-maps for the same contrast as shown in (b). (d) Pipeline for optimizing the tACS electrode montage for each individual participant to target the individual functional targets. (e) Target regions of interest used for the optimization step in SimNIBS. Individual dots represent the individual 3-mm-radius spheres around the center coordinates from the functional masks shown in (c). (f) Electrodes included in the optimized montages across participants. (g) Electric field (e) and electric field strength (normE) resulting from the optimized montage for one example participant. Only the left hemisphere is shown. Blue and red circles denote the resulting electrodes. Small red arrows on the inset show the target E-field orientation.
Figure 2
Electric field simulation results.
(a) Group average maps showing the strength of the simulated electric field (E-field strength, right) and its normal component (normal E-field, middle), separated by montage: ring-electrode montage, top; standard montage, middle, and individualized montage, bottom. Each montage is represented in the left subpanel. (b) Plots showing the individual values for the seven E-field parameters estimated per montage and participant. Each dot represents a single participant. Box plots show median (dashed vertical lines), mean (cross in the middle of the box), 25th and 75th percentiles (box edges) and extreme datapoints not considered outliers (+/–2.7σ and 99.3 percentiles, whiskers). Red crosses represent outliers (more than 1.5 times the interquartile range away from the bottom or top of the box). Note that outliers were not excluded from analyses. *p < 0.05, **p < 0.001, post-hoc paired-samples t-tests, Bonferroni corrected.
Figure 3 with 2 supplements
tACS effects and individual variability.
(a) While performing the auditory task, participants received either sham (blue) or 2 Hz tACS stimulation. The phase lag between the FM stimulus (black) and the tACS signal varied from trial to trial and was grouped into six different phase-lag bins. Each color in the figure represents a different bin. Empty black circles in the circular plot on the left mark the phase in the center of each bin. (b) Hit rates as a function of FM-stimulus phase separated by tACS condition for both sessions (S1 and S2) from three example participants. Colors follow the same coding as in (a). (c) Amplitude of the FM-stimulus driven behavioral modulation (FM-amplitude) and optimal FM-stimulus phase (FM-phase) in the sham condition. Left top plot shows the FM-amplitude values from the sham condition. Vertical lines represent the mean 95 percentile from individual surrogate distribution, session 1 dashed line, session 2 solid line. Each dot represents a single participant. Box plots show median (dashed vertical lines), mean (cross in the middle of the box), 25th and 75th percentiles (box edges) and extreme datapoints not considered outliers (+/–2.7σ and 99.3 percentiles, whiskers). Crosses represent outliers (more than 1.5 times the interquartile range away from the bottom or top of the box). Scatter plot on the right top shows the FM-amplitude in session 2 (S2) as a function of FM-amplitude in session 1 (S1). Dashed line is the diagonal and the solid line the best-fit regression line. Circular plots in the bottom panel show the optimal FM-phase for each session and the circular distance between sessions. The black line is the resultant vector. (d) Optimal FM-phase separated by tACS lag condition. Each plot shows a different phase lag according to the coordinates presented in top left legend. Color code also matches that from panel (a). For each plot, session 1 is presented in the corresponding color and session 2 in gray. The resultant vector is shown following the same convention. (e) FM-amplitude as a function of tACS phase lag for 4 single-participant examples. Solid lines show true data and dashed lines the cosine fit. Only session one is shown.
Figure 3—figure supplement 1
Gap detection performance.
Figure 3—figure supplement 2
FM-amplitude as a function of tACS phase lag.
Individual data for Figure 3e. Each plot shows data from a single participant. Solid lines show true data and dashed lines the cosine fit.
Figure 4 with 1 supplement
Group level tACS results.
(a) Amplitude of the FM-stimulus driven behavioral modulation (FM-amplitude) as a function of the realigned tACS lag conditions. Zero lag corresponds to each individual optimal tACS lag (based on a cosine fit). N = 37. (b) FM-amplitude for optimal lag and the opposite lag (x letter on top of empty circle here, pink and green semitransparent bars in a) were removed from further analyses and estimates of FM-amplitude for the positive (tACS(+)) and negative (tACS(-)) tACS half cycles were obtained by averaging the individual FM-amplitude values from the two bins adjacent to the optimal lag and its corresponding trough, respectively. (c) FM-amplitude values estimated for sham, tACS(+), and tACS(-), as described in (a, b), averaged over sessions. *p = 0.05, **p < 0.001, post-hoc paired-samples t-tests, Bonferroni corrected. N = 37. (d) FM-amplitude difference between the 3 tACS conditions in c normalized (z-scores) to the permuted distributions. In all plots in the figure, each dot represents a single participant. Box plots show median (dashed vertical lines), mean (cross in the middle of the box), 25th and 75th percentiles (box edges) and extreme datapoints not considered outliers (+/–2.7σ and 99.3 percentiles, whiskers). Crosses represent outliers (more than 1.5 times the interquartile range away from the bottom or top of the box). N = 42. S1: session 1, S2: session 2. *p = 0.05, **p < 0.001, one-sample t-test, Holm-Bonferroni corrected.
Figure 4—figure supplement 1
tACS effects separated by tACS montage.
For each session. FM-amplitude values estimated for sham. tACS(+) and tACS(-) are presented separated by tACS montage. Each dot represents a single participant. Box plots show median (vertical lines). mean (cross in the middle of the box). 25th and 75th percentiles (box edges) and extreme datapoints not considered outliers (+/–2.7σ and 99.3 percentiles. whiskers). S1: session 1. S2: session 2. N = 37.
Figure 5 with 1 supplement
Effects of tACS on behavioral signatures of entrainment were not reliable over sessions.
(a) Amplitude of the tACS effect (tACS-amplitude) for session 2 as a function of session 1. tACS-amplitude was computed as the difference between the FM-amplitude values at tACS (+) and tACS (-) in Figure 4b. Dashed line is the diagonal and gray solid line represents the regression line. Each dot represents a participant (b) Optimal tACS phase lag (tACS-phase) estimated from the cosine fits in (Figure 3e). The first two circular plots show optimal tACS-phase for each session while the third one shows the circular distance between sessions. The black line is the resultant vector. (c) The scatter plot shows the amplitude parameter obtained from fitting the cosine function to each session independently (as in b) and then averaged across sessions as a function of the fit amplitude obtained when fitting the cosine function to the data pooled across sessions. S1: session 1, S2: session 2.
Figure 5—figure supplement 1
Predicting inter-session difference in tACS-amplitude.
Scatter plots show the change in tACS-amplitude between sessions (ΔtACS-amplitude).(S1–S2) as a function of the number of days passed between sessions (ΔDays) and the time of the day absolute difference (ΔMinutes). Each dot represents a single participant. Black solid lines represent the adjusted fit.
Figure 6
Predicting tACS effects from electric field simulation.
(a) Interaction between the normal E-field and the field focality. Scatter plot on the left shows tACS effects (tACS-amplitude) as a function of the normal E-field. Each dot represents a different subject. Dot color and size represent the normalized field focality in arbitrary units. Higher values correspond to more focal electric fields. Solid lines represent the predicted adjusted response for the tACS-amplitude as a function of the normal E-field for three fixed values of focality. The plot in the right shows the main effects (blue) of focality and normal E-field and the conditional effect of each predictor given a specific value of the other (red). Horizontal lines through the effect values indicate their 95% confidence intervals. (b) Interaction between the normal E-field and the distance between the peak of the E-field and the target ROIs (Dist2Peak). Similar to (a), scatter plot on the left shows tACS-amplitude as a function of the normal E-field but dots color and size now represent the normalized Dist2Peak. Higher values correspond to shorter distance. Solid lines represent the predicted adjusted response for the tACS-amplitude as a function of the normal E-field for three fixed values of Dist2Peak. The plot in the right shows the main effects (blue) of Dist2Peak and normal E-field and the conditional effect of each predictor given a specific value of the other (red). Horizontal lines through the effect values indicate their 95% confidence intervals. Colors in the bottom for the Focality and Dist2Peak levels correspond to the same color code in the upper plots.
Author response image 1
E-field distributions for one example participant.
Brain maps show the results from the same optimization procedure described in the main manuscript but with no constraint for the current direction (top) or constraining the current direction (bottom). Note that the desired intensity of .1 V/m can be achieved when the current direction is not constrained.
Additional files
-
Supplementary file 1
Tables.
(a). MNI center coordinates for target functional regions of interest for each subject. (b) Statistics for the mixed effects logistic regression models predicting single trial gap detection performance. Models are organized from smallest to highest AIC. Δ AIC relative to winning model. The winning model is also highlighted in bold. BIC: Bayesian information criterion. (c) General linear models predicting inter-session difference on tACS-amplitude. Models are organized from smallest to highest AICc. * Δ AICc relative to winning model. The winning model is also highlighted in bold. (d) General linear models predicting inter-session absolute circular distance on tACS-phase. Models are organized from smallest to highest AICc. * Δ AICc relative to winning model. The winning model is also highlighted in bold. (e) General linear models predicting tACS effects. Models are organized from smallest to highest AICc. * Δ AICc relative to winning model. The winning model is also highlighted in bold.
- https://cdn.elifesciences.org/articles/87820/elife-87820-supp1-v1.docx
-
MDAR checklist
- https://cdn.elifesciences.org/articles/87820/elife-87820-mdarchecklist1-v1.docx
Download links
A two-part list of links to download the article, or parts of the article, in various formats.
Downloads (link to download the article as PDF)
Open citations (links to open the citations from this article in various online reference manager services)
Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)
Behavioral entrainment to rhythmic auditory stimulation can be modulated by tACS depending on the electrical stimulation field properties
eLife 12:RP87820.
https://doi.org/10.7554/eLife.87820.3
