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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 EEG under no-stimulation condition.A: Typical signals simulated in the absence of tACS stimulation (19 scalp electrodes, international 10–20 standard system). B: Real alpha activity recorded in a normal subject during wakefulness with eyes closed.
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pone-0057330-g005: Simulation of EEG under no-stimulation condition.A: Typical signals simulated in the absence of tACS stimulation (19 scalp electrodes, international 10–20 standard system). B: Real alpha activity recorded in a normal subject during wakefulness with eyes closed.

Mentions: An example of simulated EEG in the no-stimulation condition is displayed on Figure 5A. In the absence of tACS-like stimulation, simulated EEG signals display alpha-like activity. These rhythms are organised as spindles, synchronized over most of scalp EEG channels. This aspect is similar to that observed on real EEG alpha activity (Figure 5B). However, regarding real data, one can notice that the amplitude of the bursts of alpha activity is higher on parietal (P3, Pz, P4) and occipital channels (O1, O2) than on frontal electrodes while this specific topography does not appear on simulated data.


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 EEG under no-stimulation condition.A: Typical signals simulated in the absence of tACS stimulation (19 scalp electrodes, international 10–20 standard system). B: Real alpha activity recorded in a normal subject during wakefulness with eyes closed.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0057330-g005: Simulation of EEG under no-stimulation condition.A: Typical signals simulated in the absence of tACS stimulation (19 scalp electrodes, international 10–20 standard system). B: Real alpha activity recorded in a normal subject during wakefulness with eyes closed.
Mentions: An example of simulated EEG in the no-stimulation condition is displayed on Figure 5A. In the absence of tACS-like stimulation, simulated EEG signals display alpha-like activity. These rhythms are organised as spindles, synchronized over most of scalp EEG channels. This aspect is similar to that observed on real EEG alpha activity (Figure 5B). However, regarding real data, one can notice that the amplitude of the bursts of alpha activity is higher on parietal (P3, Pz, P4) and occipital channels (O1, O2) than on frontal electrodes while this specific topography does not appear on simulated data.

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