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From oscillatory transcranial current stimulation to scalp EEG changes: a biophysical and physiological modeling study.

Merlet I, Birot G, Salvador R, Molaee-Ardekani B, Mekonnen A, Soria-Frish A, Ruffini G, Miranda PC, Wendling F - PLoS ONE (2013)

Bottom Line: In order to account for tCS effects and following current biophysical models, the calculated component of the electric field normal to the cortex was used to locally influence the activity of neuronal populations.Moreover, additional information was also brought by the model at other electrode positions or stimulation frequency.This suggests that our modeling approach can be used to compare, interpret and predict changes occurring on EEG with respect to parameters used in specific stimulation configurations.

View Article: PubMed Central - PubMed

Affiliation: INSERM, Université de Rennes 1, LTSI, Rennes, France. isabelle.merlet@univ-rennes1.fr

ABSTRACT
Both biophysical and neurophysiological aspects need to be considered to assess the impact of electric fields induced by transcranial current stimulation (tCS) on the cerebral cortex and the subsequent effects occurring on scalp EEG. The objective of this work was to elaborate a global model allowing for the simulation of scalp EEG signals under tCS. In our integrated modeling approach, realistic meshes of the head tissues and of the stimulation electrodes were first built to map the generated electric field distribution on the cortical surface. Secondly, source activities at various cortical macro-regions were generated by means of a computational model of neuronal populations. The model parameters were adjusted so that populations generated an oscillating activity around 10 Hz resembling typical EEG alpha activity. In order to account for tCS effects and following current biophysical models, the calculated component of the electric field normal to the cortex was used to locally influence the activity of neuronal populations. Lastly, EEG under both spontaneous and tACS-stimulated (transcranial sinunoidal tCS from 4 to 16 Hz) brain activity was simulated at the level of scalp electrodes by solving the forward problem in the aforementioned realistic head model. Under the 10 Hz-tACS condition, a significant increase in alpha power occurred in simulated scalp EEG signals as compared to the no-stimulation condition. This increase involved most channels bilaterally, was more pronounced on posterior electrodes and was only significant for tACS frequencies from 8 to 12 Hz. The immediate effects of tACS in the model agreed with the post-tACS results previously reported in real subjects. Moreover, additional information was also brought by the model at other electrode positions or stimulation frequency. This suggests that our modeling approach can be used to compare, interpret and predict changes occurring on EEG with respect to parameters used in specific stimulation configurations.

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Simulation of scalp EEG signals under tACS stimulation. A:Calibration of the  parameter. Scalp EEG signals were simulated for 13 values of parameter  involved in the computation of the  coefficients.  corresponds to the no stimulation condition, and  correspond to the 10 Hz-tACS stimulation condition. Boxplot are obtained after averaging the mean alpha power at the POZ scalp electrode from 20 trials of simulated EEG for each condition. During tACS stimulation the alpha power at posterior electrode POZ gradually increases with the calibration factor. For , a significant increase of 14% is observed and corresponds to the percentage reported in real data at the same electrode [5]. This  value was chosen for simulations. B: Typical simulated EEG signals obtained in the no stimulation (left) or during tACS at the model peak frequency (10 Hz). C: Mean alpha power, averaged from 20 trials at each of the 19 scalp electrodes in the no stimulation vs. 10 Hz-tACS condition. Significant increase in alpha PSD is observed during tACS stimulation at most left and right channels (except for fronto-polar electrodes) as well as at posterior midline channels POZ and OZ.
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pone-0057330-g006: Simulation of scalp EEG signals under tACS stimulation. A:Calibration of the parameter. Scalp EEG signals were simulated for 13 values of parameter involved in the computation of the coefficients. corresponds to the no stimulation condition, and correspond to the 10 Hz-tACS stimulation condition. Boxplot are obtained after averaging the mean alpha power at the POZ scalp electrode from 20 trials of simulated EEG for each condition. During tACS stimulation the alpha power at posterior electrode POZ gradually increases with the calibration factor. For , a significant increase of 14% is observed and corresponds to the percentage reported in real data at the same electrode [5]. This value was chosen for simulations. B: Typical simulated EEG signals obtained in the no stimulation (left) or during tACS at the model peak frequency (10 Hz). C: Mean alpha power, averaged from 20 trials at each of the 19 scalp electrodes in the no stimulation vs. 10 Hz-tACS condition. Significant increase in alpha PSD is observed during tACS stimulation at most left and right channels (except for fronto-polar electrodes) as well as at posterior midline channels POZ and OZ.

Mentions: As mentioned in 1.4, the first step was to define the value of parameter . To proceed, we determined the value of for which an increase of the signal power in the alpha frequency band at POZ similar to that reported in [5] was observed in the model. More specifically, when applied at the alpha-peak frequency of the model (10 Hz), the tACS-like stimulation induced an elevation of the alpha power at posterior electrode POZ. This elevation gradually increased when the calibration factor was augmented (Figure 6A). In the reference study [5], an elevation of 14% in the alpha power was observed at POZ electrode. In our simulation study, this percentage value corresponded to . Therefore, the following simulations were calibrated by fixing .


From oscillatory transcranial current stimulation to scalp EEG changes: a biophysical and physiological modeling study.

Merlet I, Birot G, Salvador R, Molaee-Ardekani B, Mekonnen A, Soria-Frish A, Ruffini G, Miranda PC, Wendling F - PLoS ONE (2013)

Simulation of scalp EEG signals under tACS stimulation. A:Calibration of the  parameter. Scalp EEG signals were simulated for 13 values of parameter  involved in the computation of the  coefficients.  corresponds to the no stimulation condition, and  correspond to the 10 Hz-tACS stimulation condition. Boxplot are obtained after averaging the mean alpha power at the POZ scalp electrode from 20 trials of simulated EEG for each condition. During tACS stimulation the alpha power at posterior electrode POZ gradually increases with the calibration factor. For , a significant increase of 14% is observed and corresponds to the percentage reported in real data at the same electrode [5]. This  value was chosen for simulations. B: Typical simulated EEG signals obtained in the no stimulation (left) or during tACS at the model peak frequency (10 Hz). C: Mean alpha power, averaged from 20 trials at each of the 19 scalp electrodes in the no stimulation vs. 10 Hz-tACS condition. Significant increase in alpha PSD is observed during tACS stimulation at most left and right channels (except for fronto-polar electrodes) as well as at posterior midline channels POZ and OZ.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585369&req=5

pone-0057330-g006: Simulation of scalp EEG signals under tACS stimulation. A:Calibration of the parameter. Scalp EEG signals were simulated for 13 values of parameter involved in the computation of the coefficients. corresponds to the no stimulation condition, and correspond to the 10 Hz-tACS stimulation condition. Boxplot are obtained after averaging the mean alpha power at the POZ scalp electrode from 20 trials of simulated EEG for each condition. During tACS stimulation the alpha power at posterior electrode POZ gradually increases with the calibration factor. For , a significant increase of 14% is observed and corresponds to the percentage reported in real data at the same electrode [5]. This value was chosen for simulations. B: Typical simulated EEG signals obtained in the no stimulation (left) or during tACS at the model peak frequency (10 Hz). C: Mean alpha power, averaged from 20 trials at each of the 19 scalp electrodes in the no stimulation vs. 10 Hz-tACS condition. Significant increase in alpha PSD is observed during tACS stimulation at most left and right channels (except for fronto-polar electrodes) as well as at posterior midline channels POZ and OZ.
Mentions: As mentioned in 1.4, the first step was to define the value of parameter . To proceed, we determined the value of for which an increase of the signal power in the alpha frequency band at POZ similar to that reported in [5] was observed in the model. More specifically, when applied at the alpha-peak frequency of the model (10 Hz), the tACS-like stimulation induced an elevation of the alpha power at posterior electrode POZ. This elevation gradually increased when the calibration factor was augmented (Figure 6A). In the reference study [5], an elevation of 14% in the alpha power was observed at POZ electrode. In our simulation study, this percentage value corresponded to . Therefore, the following simulations were calibrated by fixing .

Bottom Line: In order to account for tCS effects and following current biophysical models, the calculated component of the electric field normal to the cortex was used to locally influence the activity of neuronal populations.Moreover, additional information was also brought by the model at other electrode positions or stimulation frequency.This suggests that our modeling approach can be used to compare, interpret and predict changes occurring on EEG with respect to parameters used in specific stimulation configurations.

View Article: PubMed Central - PubMed

Affiliation: INSERM, Université de Rennes 1, LTSI, Rennes, France. isabelle.merlet@univ-rennes1.fr

ABSTRACT
Both biophysical and neurophysiological aspects need to be considered to assess the impact of electric fields induced by transcranial current stimulation (tCS) on the cerebral cortex and the subsequent effects occurring on scalp EEG. The objective of this work was to elaborate a global model allowing for the simulation of scalp EEG signals under tCS. In our integrated modeling approach, realistic meshes of the head tissues and of the stimulation electrodes were first built to map the generated electric field distribution on the cortical surface. Secondly, source activities at various cortical macro-regions were generated by means of a computational model of neuronal populations. The model parameters were adjusted so that populations generated an oscillating activity around 10 Hz resembling typical EEG alpha activity. In order to account for tCS effects and following current biophysical models, the calculated component of the electric field normal to the cortex was used to locally influence the activity of neuronal populations. Lastly, EEG under both spontaneous and tACS-stimulated (transcranial sinunoidal tCS from 4 to 16 Hz) brain activity was simulated at the level of scalp electrodes by solving the forward problem in the aforementioned realistic head model. Under the 10 Hz-tACS condition, a significant increase in alpha power occurred in simulated scalp EEG signals as compared to the no-stimulation condition. This increase involved most channels bilaterally, was more pronounced on posterior electrodes and was only significant for tACS frequencies from 8 to 12 Hz. The immediate effects of tACS in the model agreed with the post-tACS results previously reported in real subjects. Moreover, additional information was also brought by the model at other electrode positions or stimulation frequency. This suggests that our modeling approach can be used to compare, interpret and predict changes occurring on EEG with respect to parameters used in specific stimulation configurations.

Show MeSH
Related in: MedlinePlus