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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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Related in: MedlinePlus

Spatial distribution of the externally-applied electric field and subsequent field effects. A:Spatial distribution of the magnitude of the electric field using two virtual electrodes over the occipital regions and after applying a 1.12 mA current through the anode. The amplitude of the electric field is mapped on a mesh of the WM/GM interface. B: Mean field effect. The effect of the electric field depending on the orientation of pyramidal cells within the neocortex, is accounted for by calculating the radial component of the applied field  (scalar product between the electric field and the unit vector parallel to the pyramidal cell main axis) at each triangle of the mesh of the WM/GM interface.  values obtained for each triangle are then averaged over each of the 66 anatomical macro-regions manually outlined according to [35]. The resulting  coefficients represent the mean effect of the electric field over each macro-region.
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pone-0057330-g004: Spatial distribution of the externally-applied electric field and subsequent field effects. A:Spatial distribution of the magnitude of the electric field using two virtual electrodes over the occipital regions and after applying a 1.12 mA current through the anode. The amplitude of the electric field is mapped on a mesh of the WM/GM interface. B: Mean field effect. The effect of the electric field depending on the orientation of pyramidal cells within the neocortex, is accounted for by calculating the radial component of the applied field (scalar product between the electric field and the unit vector parallel to the pyramidal cell main axis) at each triangle of the mesh of the WM/GM interface. values obtained for each triangle are then averaged over each of the 66 anatomical macro-regions manually outlined according to [35]. The resulting coefficients represent the mean effect of the electric field over each macro-region.

Mentions: Using these parameters, the field distribution was calculated as described in section 1.2, and mapped on the WM surface mesh (representing the WM/GM interface) (Figure 4A). At each triangle of the mesh, the radial component of the externally-applied field (i.e. component parallel to the neuron main axis) , was obtained bywhere represents the electric field vector at the 3D position , stands for the unit vector perpendicular to the triangle surface (i.e. parallel to the somatodendritic axis of pyramidal cells) and for a calibration constant.


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)

Spatial distribution of the externally-applied electric field and subsequent field effects. A:Spatial distribution of the magnitude of the electric field using two virtual electrodes over the occipital regions and after applying a 1.12 mA current through the anode. The amplitude of the electric field is mapped on a mesh of the WM/GM interface. B: Mean field effect. The effect of the electric field depending on the orientation of pyramidal cells within the neocortex, is accounted for by calculating the radial component of the applied field  (scalar product between the electric field and the unit vector parallel to the pyramidal cell main axis) at each triangle of the mesh of the WM/GM interface.  values obtained for each triangle are then averaged over each of the 66 anatomical macro-regions manually outlined according to [35]. The resulting  coefficients represent the mean effect of the electric field over each macro-region.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0057330-g004: Spatial distribution of the externally-applied electric field and subsequent field effects. A:Spatial distribution of the magnitude of the electric field using two virtual electrodes over the occipital regions and after applying a 1.12 mA current through the anode. The amplitude of the electric field is mapped on a mesh of the WM/GM interface. B: Mean field effect. The effect of the electric field depending on the orientation of pyramidal cells within the neocortex, is accounted for by calculating the radial component of the applied field (scalar product between the electric field and the unit vector parallel to the pyramidal cell main axis) at each triangle of the mesh of the WM/GM interface. values obtained for each triangle are then averaged over each of the 66 anatomical macro-regions manually outlined according to [35]. The resulting coefficients represent the mean effect of the electric field over each macro-region.
Mentions: Using these parameters, the field distribution was calculated as described in section 1.2, and mapped on the WM surface mesh (representing the WM/GM interface) (Figure 4A). At each triangle of the mesh, the radial component of the externally-applied field (i.e. component parallel to the neuron main axis) , was obtained bywhere represents the electric field vector at the 3D position , stands for the unit vector perpendicular to the triangle surface (i.e. parallel to the somatodendritic axis of pyramidal cells) and for a calibration constant.

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