Measurements and models of electric fields in the in vivo human brain during transcranial electric stimulation

  1. Yu Huang
  2. Anli A Liu  Is a corresponding author
  3. Belen Lafon
  4. Daniel Friedman
  5. Michael Dayan
  6. Xiuyuan Wang
  7. Marom Bikson
  8. Werner K Doyle
  9. Orrin Devinsky
  10. Lucas C Parra  Is a corresponding author
  1. City College of the City University of New York, United States
  2. New York University School of Medicine, United States
  3. Mayo Clinic, United States
9 figures and 1 table

Figures

Location of the invasive recording electrodes and transcranial electrical stimulation electrodes in the 10 patients tested.

Electrodes measuring from the cortical surface (64-contact grids, 8-contact strips) are indicated as black dots and depth electrodes (between 6–8 contacts each) as red dots. Square stimulation …

https://doi.org/10.7554/eLife.18834.002
Prediction of electric field with calibrated models for various electrode montages at 1 mA stimulation intensity.

(B) Histogram of electric field magnitude for the montage used on Subject P03 (same as in Figure 5) and Subject P014. (C) Corresponding spatial distributions on cortical surface. (D) Cross-section …

https://doi.org/10.7554/eLife.18834.003
Voltage recordings across multiple intracranial locations for sinusoidal transcranial alternating current stimulation for the first subject tested (P03).

Magnitude and sign are estimated by fitting a sinusoid to the voltage fluctuations at each electrode location. (A) Voltage recordings at multiple intracranial recording locations are linear with …

https://doi.org/10.7554/eLife.18834.004
Example of realistic model for Subject P06.

Each patient's detailed anatomy was obtained by segmenting T1-weighted MR images into six tissue types: scalp, skull, CSF, gray matter, white matter, and air. Additionally, to capture the surgical …

https://doi.org/10.7554/eLife.18834.005
Voltage and electric field for measurements and model.

All values are calibrated to 1 mA stimulation. (A) False-color representation of measured voltages for patient P03. (B) Voltages from the corresponding individualized model across the cortical …

https://doi.org/10.7554/eLife.18834.006
Figure 5—source data 1

Animated 3D renderings of the recorded and model-predicted voltages for each subject, and the absolute difference between the two.

The predicted values are from the individually optimized models.

https://doi.org/10.7554/eLife.18834.007
Electric field predicted with individually calibrated models under 1 mA stimulation.

(A) Summary of electric field magnitudes for all subjects. The four different configurations of stimulation electrodes in Subject P014 are indicated as P014A–P014D. Also shown are values for a few …

https://doi.org/10.7554/eLife.18834.008
Comparison of recorded values with model predictions using literature conductivity values for Subject P03 scaled to 1 mA.

Points falling on the dashed blue line represent perfect prediction (slope s = 1). The literature values gives close estimates of electric field magnitude (measurements are 72% of predicted values, s

https://doi.org/10.7554/eLife.18834.009
Figure 8 with 1 supplement
Prediction accuracy for models using various conductivity choices.

(A, B) Correlation indicates the accuracy of the spatial distribution. (C, D) Slope indicates the accuracy of the magnitude estimate. Results are shown for three categories of models: models using …

https://doi.org/10.7554/eLife.18834.010
Figure 8—figure supplement 1
Estimation of the sensitivity of the fitting procedure to small variations in the conductivity values.

(A–C) For conductivities that were fit to the data (skull, scalp, white matter) we numerically evaluated the Cramér-Rao bound, shown here as error bars around the optimal values for each subject, …

https://doi.org/10.7554/eLife.18834.011
Performance of various modeling approaches.

IM-CSF: This ‘intact model’ is based on the pre-surgical MRI and does not include craniotomy, recording electrodes, etc., and does not model CSF either; IM: intact model including CSF; RMcut: …

https://doi.org/10.7554/eLife.18834.012

Tables

Table 1

Models with different complexities

https://doi.org/10.7554/eLife.18834.013
ModelDetailsAbbreviation
intact model without CSFgray, white, skull, scalp, air, stim electrodesIM-CSF
intact modelgray, white, CSF, skull, scalp, air, stim electrodesIM
realistic modelintact model with craniotomy and surgical instrumentRM
realistic model with limited FOVsame as realistic model except truncated at the bottom of the skullRMcut
realistic model with inhomogeneous skullskull is modeled as 3-layered structureRM + 3skull
realistic model with anisotropic brain derived from DTI datadirect mappingRM+DTI
volume normalizedRM+DTI/VN
volume constrainedRM+DTI/VC
equivalent isotropic traceRM+DTI/EIT

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