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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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Generation of alpha-like cortical activity in the neuronal population model.A: Typical alpha-like signal (alpha peak around 10 Hz) produced by the model at the level of a single population for appropriate setting of parameters (see table 1) B: An example of signals obtained in the model with N populations (same set of parameters as in A) when no connectivity is present among populations. Alpha-like activity is generated at the level of each population. This activity is desynchronized among populations. C: An example of signals obtained in the model with N populations (same set of parameters as in A), when a “vertical” connectivity pattern is used. In that case, an additional population (N+1th) is added as a common synchronizer. This population called “subcortical” is unidirectionally coupled with the N other populations in order to mimic the thalamic input. The “sub-cortical” population also receives a direct low frequency input in order to mimic the synchronizing effect of cortical delta oscillations on the thalamus. Under these conditions, alpha-like activity is synchronized among the N populations.
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pone-0057330-g001: Generation of alpha-like cortical activity in the neuronal population model.A: Typical alpha-like signal (alpha peak around 10 Hz) produced by the model at the level of a single population for appropriate setting of parameters (see table 1) B: An example of signals obtained in the model with N populations (same set of parameters as in A) when no connectivity is present among populations. Alpha-like activity is generated at the level of each population. This activity is desynchronized among populations. C: An example of signals obtained in the model with N populations (same set of parameters as in A), when a “vertical” connectivity pattern is used. In that case, an additional population (N+1th) is added as a common synchronizer. This population called “subcortical” is unidirectionally coupled with the N other populations in order to mimic the thalamic input. The “sub-cortical” population also receives a direct low frequency input in order to mimic the synchronizing effect of cortical delta oscillations on the thalamus. Under these conditions, alpha-like activity is synchronized among the N populations.

Mentions: Neuronal population models were originally developed to study the mechanisms underlying the generation of alpha activity in the cortex [13]. It is well-known that these models can easily reach an oscillating behaviour after appropriate setting of i) connectivity parameters and ii) rise and decay times of excitatory (glutamatergic) and inhibitory (GABAergic) average post-synaptic potentials (PSPs). In particular, at the level of a single population, when these parameters are properly adjusted, oscillations around 10 Hz become prominent in the model signal output [14]. These oscillations closely resemble real alpha activity (Figure 1A).


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)

Generation of alpha-like cortical activity in the neuronal population model.A: Typical alpha-like signal (alpha peak around 10 Hz) produced by the model at the level of a single population for appropriate setting of parameters (see table 1) B: An example of signals obtained in the model with N populations (same set of parameters as in A) when no connectivity is present among populations. Alpha-like activity is generated at the level of each population. This activity is desynchronized among populations. C: An example of signals obtained in the model with N populations (same set of parameters as in A), when a “vertical” connectivity pattern is used. In that case, an additional population (N+1th) is added as a common synchronizer. This population called “subcortical” is unidirectionally coupled with the N other populations in order to mimic the thalamic input. The “sub-cortical” population also receives a direct low frequency input in order to mimic the synchronizing effect of cortical delta oscillations on the thalamus. Under these conditions, alpha-like activity is synchronized among the N populations.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0057330-g001: Generation of alpha-like cortical activity in the neuronal population model.A: Typical alpha-like signal (alpha peak around 10 Hz) produced by the model at the level of a single population for appropriate setting of parameters (see table 1) B: An example of signals obtained in the model with N populations (same set of parameters as in A) when no connectivity is present among populations. Alpha-like activity is generated at the level of each population. This activity is desynchronized among populations. C: An example of signals obtained in the model with N populations (same set of parameters as in A), when a “vertical” connectivity pattern is used. In that case, an additional population (N+1th) is added as a common synchronizer. This population called “subcortical” is unidirectionally coupled with the N other populations in order to mimic the thalamic input. The “sub-cortical” population also receives a direct low frequency input in order to mimic the synchronizing effect of cortical delta oscillations on the thalamus. Under these conditions, alpha-like activity is synchronized among the N populations.
Mentions: Neuronal population models were originally developed to study the mechanisms underlying the generation of alpha activity in the cortex [13]. It is well-known that these models can easily reach an oscillating behaviour after appropriate setting of i) connectivity parameters and ii) rise and decay times of excitatory (glutamatergic) and inhibitory (GABAergic) average post-synaptic potentials (PSPs). In particular, at the level of a single population, when these parameters are properly adjusted, oscillations around 10 Hz become prominent in the model signal output [14]. These oscillations closely resemble real alpha activity (Figure 1A).

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