EFMouse: 1 x Back montage
EFMouse is a Matlab tool for electric field modelling in the mouse brain.
This notebook reproduces results for the 1 x Back montage in:
Sanchez-Romero R., Akyuz, S., & Krekelberg, B. (2025). EFMouse: a toolbox to model electric fields in the mouse brain. bioRxiv. https://doi.org/10.1101/2024.07.25.605227
The notebook is also an introductory tutorial to simulate other montages.
Developed by Ruben Sanchez-Romero and Bart Krekelberg,
Rutgers Newark, Center for Molecular and Behavioral Neuroscience.
For support open an issue in https://github.com/klabhub/EFMouse/issues.
Introduction
EFMouse combines several elements from previous work:
- Anatomical data from the Digimouse project.
- A refined finite element mesh of the Digimouse by Alekseichuk et al., (2019), Neuroimage.
- Matlab code and inspiration from the ROAST toolbox.
- The GetDP finite element method (FEM) solver (v 3.5.0).
- The Allen mouse brain atlas.
Key new functionality includes:
- Positioning electrodes in arbitrary locations in and on the mouse body.
- Modeling craniotomies in the mouse skull.
- Analyzing the electric field in user-defined regions of interest
- Analyzing the electric field in brain regions defined in the Allen mouse atlas.
- A measure of relative focality of the electric field.
- A measure of direction homogeneity of the electric field.
For details see Sanchez-Romero et al., (2025) and EFMouse.m Matlab code.
Typical workflow
The typical workflow to generate a model consists of several stages
- Stage.INIT : Initialize.
- Stage.MESH : Create elecrodes and (optionally) a craniotomy.
- Stage.EXPORT : Export files for the FEM solver GetDP.
- Stage.GETDP : Run the FEM solver.
- Stage.ATLAS : Map the results to the Allen mouse atlas.
Stage INIT: Initialize
We start by setting up the basic parameters of the EFMouse object:
o = EFMouse; % Create a default empty object of the class EFMouse
o.ID = '1xBack'; % A name/tag for this simulation.
o.dir = '/Users/rubensanchez/desktop/efmouse_sim/1xBack'; % Results and the object (1xBack.mat) will be saved here.
o.log = true; % Create a log file.
Note: The log file is created but doesn't update when running a simulation from a notebook (like here). It will properly update when running EFMouse directly from the Matlab command line.
initialize() creates the folder to store the results. With overwrite=true, anything in this folder will be deleted.
o.initialize(overwrite=true);
The initialized EFMouse o object contains the default mouse mesh (without stimulation electrodes). Let's visualize it.
plotMesh(o,tissue="gray")
The mesh is pretty dense, so it may look like a black blob. The olfactory bulbs are visible on the top. In a regular figure window, you can use the Matlab figure tools to rotate or zoom. (You can also adapt the plotMesh() function in EFMouse.m to modifiy the figure directly.)
Stage MESH: Create electrodes and (optionally) a craniotomy
Now we define a 1 x Back stimulation montage, targeting visual areas. The surface type is an electrode that is placed on top of the animal (simulating how gel would be placed on the skin). We simulate a circular stimulation anode targeting the visual areas, and a rectangular return cathode in the mouse back.
o.addElectrode(tag = "Anode",current = 0.2,type="surface",shape="circle",center= [-3.5,27.5,6],radius=0.6, thickness=1);
o.addElectrode(tag = "Cathode",current = -0.2,type="surface",shape="rectangle",center=[-1,-12,10],length=15,width=15,thickness=1);
To update the model with the electrodes, we run the pipeline to Stage.MESH.
We can set show=false, and then plot using plotMesh() showing skin tissue to visualize the electrode in the back. We can also adjust the y axis dimensions to visualize the whole body.
o.run(targetStage=Stage.MESH,show=false)
Compute stage MESH
EF Mouse Model (label: 1xBack) in directory /Users/rubensanchez/desktop/efmouse_sim/1xBack (stage=INIT).
-Meshing 2 electrodes-
Closest skin node is 0.4 away from the Anode electrode target position.
Closest skin node is 0.5 away from the Cathode electrode target position.
Stage MESH complete - 26.4415 seconds
plotMesh(o,tissue="skin")
This mesh shows the electrodes in red (anode) and blue (cathode).
Stage EXPORT: Export the mesh and model
Up until this stage, all changes were internal to the Matlab object (saved in 1xBack.mat), now we export files that the FEM solver GetDP can read. The .msh file contains information on the mesh (all the nodes, elements, labels and boundaries), and the .pro file tells GetDP which partial differential equations (PDE) model it needs to solve in this mesh.
o.run(targetStage=Stage.EXPORT)
Compute stage EXPORT
----Starting saveMesh...19-Jun-2025 10:05:54
----saveMesh elapsed time: 11.7843 seconds
----Starting savePro...19-Jun-2025 10:06:06
----savePro elapsed time: 0.0146 seconds
Stage EXPORT complete - 7.9396 seconds
For troubleshooting, have a look at the .pro file in the project folder; it contains all the model specifications, including conductivity (in siemens per meter S/m) for the different tissues/elements.
type(file(o,"PRO"))
/*
.pro file created by EFMouse on 19-Jun-2025 10:06:06
ID: 1xBack
Dir: /Users/rubensanchez/desktop/efmouse_sim/1xBack
*/
Group {
gray = Region[1];
csf = Region[2];
bone = Region[3];
skin = Region[4];
eye = Region[5];
Anode = Region[6];
Cathode = Region[7];
boundaryAnode = Region[8];
boundaryCathode = Region[9];
DomainC = Region[{gray,csf,bone,skin,eye,Anode,Cathode}];
AllDomain = Region[{gray,csf,bone,skin,eye,Anode,Cathode,boundaryAnode,boundaryCathode}];
}
Function {
sigma[gray] = 0.275;
sigma[csf] = 1.654;
sigma[bone] = 0.01;
sigma[skin] = 0.465;
sigma[eye] = 0.5;
sigma[Anode] = 0.3;
sigma[Cathode] = 0.3;
du_dnAnode[] = 110.774083;
du_dnCathode[] = -0.524215;
}
Jacobian {
{ Name Vol ;
Case {
{ Region All ; Jacobian Vol ; }
}
}
{ Name Sur ;
Case {
{ Region All ; Jacobian Sur ; }
}
}
}
Integration {
{ Name GradGrad ;
Case { {Type Gauss ;
Case { { GeoElement Triangle ; NumberOfPoints 3 ; }
{ GeoElement Quadrangle ; NumberOfPoints 4 ; }
{ GeoElement Tetrahedron ; NumberOfPoints 4 ; }
{ GeoElement Hexahedron ; NumberOfPoints 6 ; }
{ GeoElement Prism ; NumberOfPoints 9 ; } }
}
}
}
}
FunctionSpace {
{ Name Hgrad_v_Ele; Type Form0;
BasisFunction {
// v = v s , for all nodes
// n n
{ Name sn; NameOfCoef vn; Function BF_Node;
Support AllDomain; Entity NodesOf[ All ]; }
}
}
}
Formulation {
{ Name Electrostatics_v; Type FemEquation;
Quantity {
{ Name v; Type Local; NameOfSpace Hgrad_v_Ele; }
}
Equation {
Galerkin { [ sigma[] * Dof{d v} , {d v} ]; In DomainC;
Jacobian Vol; Integration GradGrad; }
Galerkin{ [ -du_dnAnode[], {v} ]; In boundaryAnode ; Jacobian Sur; Integration GradGrad;}
Galerkin{ [ -du_dnCathode[], {v} ]; In boundaryCathode ; Jacobian Sur; Integration GradGrad;}
}
}
}
Resolution {
{ Name EleSta_v;
System {
{ Name Sys_Ele; NameOfFormulation Electrostatics_v; }
}
Operation {
Generate[Sys_Ele]; Solve[Sys_Ele]; SaveSolution[Sys_Ele];
}
}
}
PostProcessing {
{ Name EleSta_v; NameOfFormulation Electrostatics_v;
Quantity {
{ Name v;
Value {
Local { [ {v} ]; In AllDomain; Jacobian Vol; }
}
}
{ Name e;
Value {
Local { [ -{d v} ]; In AllDomain; Jacobian Vol; }
}
}
}
}
}
PostOperation {
{ Name Map; NameOfPostProcessing EleSta_v;
Operation {
Print [ v, OnElementsOf DomainC, File "/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack_v.pos", Format NodeTable ];
Print [ e, OnElementsOf DomainC, Smoothing, File "/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack_e.pos", Format NodeTable ];
}
}
}
This file can be opened in the GetDP gui to run it manually, but Stage.GETDP runs it for you.
Stage GETDP: Run GetDP
It will take GetDP between 15 and 30 minutes to compute the solutions of the Laplace equation (on 2024 Mac or Windows hardware). The results are saved in _e.pos and _v.pos files (in GetDP format). In the o object the results are saved as .field and .voltage.
o.run(targetStage=Stage.GETDP,show=false);
Compute stage GETDP
Info : Running '/Users/rubensanchez/Desktop/Klab/EFMouse/lib/getdp-3.5.0/bin/getdpMac /Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack.pro -solve EleSta_v -msh /Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack.msh -pos Map' [GetDP 3.5.0, 1 node, max. 1 thread]
Info : Started (Thu Jun 19 10:06:47 2025, Wall = 0.00131297s, CPU = 0.014285s, Mem = 4.28516Mb)
Info : Initializing Gmsh
Info : Loading problem definition '/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack.pro'
Info : Selected Resolution 'EleSta_v'
Info : Loading Geometric data '/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack.msh'
Info : System 'Sys_Ele' : Real
□[34mP r e - P r o c e s s i n g . . .□[0m
Info : Treatment Formulation 'Electrostatics_v'
0% : Pre-processing
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90% : Pre-processing
Info : System 1/1: 1031584 Dofs
Info : (Wall = 13.2647s, CPU = 13.0102s, Mem = 688.586Mb)
□[34mE n d P r e - P r o c e s s i n g□[0m
□[34mP r o c e s s i n g . . .□[0m
Info : Generate[Sys_Ele]
0% : Processing (Generate)
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Info : Solve[Sys_Ele]
Info : N: 1031584 - preonly lu mumps
Info : 0 KSP Residual norm 6.653878773112e+01
Info : 1 KSP Residual norm 4.624979468015e-04
Info : SaveSolution[Sys_Ele]
Info : (Wall = 204.6s, CPU = 826.097s, Mem = 5173.75Mb)
□[34mE n d P r o c e s s i n g□[0m
□[34mP o s t - P r o c e s s i n g . . .□[0m
Info : NameOfSystem not set in PostProcessing: selected 'Sys_Ele'
Info : Selected PostProcessing 'EleSta_v'
Info : Selected Mesh '/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack.msh'
Info : PostOperation 'Map' 1/2
> '/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack_v.pos'
0% : Post-processing (Compute)
10% : Post-processing (Compute)
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Info : PostOperation 'Map' 2/2
> '/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack_e.pos'
0% : Post-processing (Generate)
10% : Post-processing (Generate)
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0% : Post-processing (Compute)
Info : Smoothing (phase 1)
Info : Smoothing (phase 2)
Info : (Wall = 304.653s, CPU = 911.126s, Mem = 5173.75Mb)
□[34mE n d P o s t - P r o c e s s i n g□[0m
Info : Stopped (Thu Jun 19 10:11:53 2025, Wall = 305.589s, CPU = 911.2s, Mem = 5173.75Mb)
Stage GETDP complete - 317.1984 seconds
Use the plotEf() function to visualize the electric field in the x direction, and then the electric field magnitude.
plotEf(o,type='eX',percentile=98, tissue='gray');
----Starting plotEf...19-Jun-2025 10:35:26
----plotEf elapsed time: 0.8674 seconds
plotEf(o,type='eMag',percentile=98,tissue='gray')
----Starting plotEf...19-Jun-2025 10:35:27
----plotEf elapsed time: 0.5084 seconds
We can also use plotEf() to visualize a brain slice perpendicular to a given axis. Here we show a frontal/coronal plane slice (perpendicular to the y axis) in the position of the anode electrode, a sagittal slice and a horizontal slice.
plotEf(o,type='eMag',percentile=98,tissue='gray',slice = true, slice_ax = "y",slice_pos = 27)
----Starting plotEf...19-Jun-2025 10:35:54
----plotEf elapsed time: 0.4914 seconds
plotEf(o,type='eMag',percentile=98,tissue='gray',slice = true, slice_ax = "x",slice_pos = -2)
----Starting plotEf...19-Jun-2025 10:35:55
----plotEf elapsed time: 0.4159 seconds
plotEf(o,type='eMag',percentile=98,tissue='gray',slice = true, slice_ax = "z",slice_pos = 3.5)
----Starting plotEf...19-Jun-2025 10:35:55
----plotEf elapsed time: 0.3739 seconds
Tissue Based Analysis
In general, we focus on the brain, but if necessary, we can compute electric field estimates for the rest of the mouse body for a full characterization of the anatomical effects of the electrical stimulation protocol.
See Sanchez-Romero et al., (2025) for a full description of the electric field metrics.
summary = analyzeTissue(o,["skin" "gray"]);
----Starting analyzeTissue...19-Jun-2025 10:36:03
Electric field summary statistics for skin tissue
mean median std min max
_______ _________ ______ __________ ______
eX 0.28675 0.0031563 3.2945 -110.54 175.73
eY -1.0622 -0.55873 2.6952 -155.08 136.56
eZ -0.5017 0.02422 5.9647 -309.89 42.628
eMag 1.9837 1.041 7.157 9.6311e-07 346.72
[Homogeneity ranges from 0 to 1]
Homogeneity = 0.5874, for ef_norm_mean: (0.044 -0.562 0.165)
Electric field summary statistics for gray tissue
mean median std min max
_______ ________ _______ _______ ______
eX 1.0979 0.90471 0.85473 -1.5353 6.506
eY -0.6353 -0.44815 1.2741 -5.579 3.5553
eZ -1.63 -1.3078 1.1555 -10.085 0.2416
eMag 2.4442 2.1123 1.4074 0.21545 11.245
[Homogeneity ranges from 0 to 1]
Homogeneity = 0.8408, for ef_norm_mean: (0.472 -0.209 -0.664)
ROI Analysis
Now that we have the field estimates for each node in the mesh, we can do an ROI based analysis. For instance, a box ROI.
For the relative focality, the reference area is the rest of the gray tissue.
See Sanchez-Romero et al. (2025), for relative focality and homogeneity definitions.
roi.center = [-3.5 27.5 3.5];
roi.width = 2; % Left/Right
roi.length = 2; % Posterior/Anterior
roi.thickness =1; % Inferior/Superior
summary = analyzeRoi(o,roi,plot=true,foc_percentile_max=99.9,foc_threshold=40); % Define values for relative focality metric.
----Starting analyzeRoi...30-Jun-2025 11:45:26
Electric field summary statistics for a box roi in gray
mean median std min max
_______ ________ _______ _______ _______
eX 1.2422 1.3712 0.92365 -1.5353 3.2231
eY -1.0341 -0.96759 1.0952 -4.2428 1.3652
eZ -5.1872 -4.9696 0.82864 -7.9745 -3.2652
eMag 5.6217 5.3833 0.80884 4.3393 8.3397
[Relative focality ranges from 0 to 1]
Relative focality = 0.7937, with 160508 reference nodes (cutoff: eMag > 40.00% of the target area max (99.90th percentile))
[Homogeneity ranges from 0 to 1]
Homogeneity = 0.9658, for ef_norm_mean: (0.216 -0.186 -0.923)
% Rotate and zoom to view the (yellow) box ROI underneath the stimulation electrode
For comparison, define an analogous box ROI but in the right hemisphere.
roiRight.center(1) =-1* roi.center(1)
roiRight =
shape: 'box'
center: [3.5000 27.5000 3.5000]
width: 2
length: 2
thickness: 1
summary = analyzeRoi(o,roiRight,plot=true,foc_percentile_max=99.9,foc_threshold=40);
----Starting analyzeRoi...30-Jun-2025 11:45:28
Electric field summary statistics for a box roi in gray
mean median std min max
________ ________ _______ _______ ________
eX 1.282 1.2895 0.2134 0.74629 1.8291
eY -0.70015 -0.67334 0.18862 -1.2473 -0.37734
eZ -1.0859 -1.0879 0.12783 -1.3629 -0.76982
eMag 1.8329 1.8273 0.22578 1.3278 2.4107
[Relative focality ranges from 0 to 1]
Relative focality = 0.0885, with 160925 reference nodes (cutoff: eMag > 40.00% of the target area max (99.90th percentile))
[Homogeneity ranges from 0 to 1]
Homogeneity = 0.9931, for ef_norm_mean: (0.698 -0.382 -0.594)
% Rotate and zoom to view the (yellow) box ROI in the right hemisphere
Stage ATLAS: Volumetric/Atlas Analysis
The mesh coordinates are not particularly intuitive, and you may want to estimate electric fields in specific brain areas (as defined in an atlas). EFMouse does this in reference to the Allen Mouse Brain Atlas.
To use this, we first have to map the mesh-based results to the Allen Atlas. This is Stage ATLAS of the pipeline. This stage first exports the mesh-based results to a volume (using linear interpolation) and then uses the FLIRT tool in FSL to transform this volume to the coordinates of the Allen Atlas. Note that the alignment between the Digimouse mesh and the Allen Atlas is not perfect because they are based on different imaging modalities (and different mouse strains). (See Sanchez-Romero et al., (2025) for more details.)
This will fail if FSL is not installed.
o.run(targetStage=Stage.ATLAS,startStage=Stage.ATLAS)
Compute stage ATLAS
----Starting computeVoxelSpace...19-Jun-2025 10:48:15
----Exporting to NIFTI volumes
---/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack_efm.nii.gz created
---/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack_efX.nii.gz created
---/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack_efY.nii.gz created
---/Users/rubensanchez/desktop/efmouse_sim/1xBack/1xBack_efZ.nii.gz created
----computeVoxelSpace elapsed time: 8.6582 seconds
Stage ATLAS complete - 16.7342 seconds
Atlas Based Analysis
Once stage ATLAS has completed, we can query electric fields based on a region that is defined in the Allen Atlas. For instance: 'Visual areas' for the left hemisphere.
For the relative focality the reference area is the rest of the Allen atlas "Isocortex".
T = analyzeAtlas(o,"Visual areas",hemisphere="left",foc_threshold=40,foc_percentile_max=99.9,foc_reference='Isocortex');
----Starting analyzeAtlas...30-Jun-2025 11:46:33
Area: Visual areas (1.0% of brain) , hemisphere left
mean median std min max
_______ _______ ______ _________ ______
eX 3.2881 3.7586 1.6303 -0.7873 6.2618
eY -1.2745 -1.0903 1.5853 -5.1701 2.4158
eZ -5.7606 -5.9788 1.8961 -9.7006 0
eMag 7.0702 7.5057 2.1122 0.0027404 10.824
[Relative focality ranges from 0 to 1]
Relative focality = 0.8840, with 92410 reference voxels (cutoff: eMag > 40.00% of the target area max (99.90th percentile))
[Homogeneity ranges from 0 to 1]
Homogeneity = 0.9499, for ef_norm_mean: (0.460 -0.183 -0.811)
----analyzeAtlas elapsed time: 0.5005 seconds
For comparison, we can query results for the right hemisphere, which is contra-lateral from the targeted area.
T = analyzeAtlas(o,"Visual areas",hemisphere="right",foc_threshold=40,foc_percentile_max=99.9,foc_reference='Isocortex');
----Starting analyzeAtlas...30-Jun-2025 11:46:33
Area: Visual areas (1.0% of brain) , hemisphere right
mean median std min max
________ ________ _______ _________ ________
eX 1.6462 1.7634 0.74693 0.0020763 2.8952
eY -0.87165 -0.95037 0.42619 -1.7359 0.016211
eZ -1.1141 -1.1812 0.51421 -1.976 0
eMag 2.1982 2.3833 0.94074 0.0026452 3.569
[Relative focality ranges from 0 to 1]
Relative focality = 0.1967, with 92457 reference voxels (cutoff: eMag > 40.00% of the target area max (99.90th percentile))
[Homogeneity ranges from 0 to 1]
Homogeneity = 0.9870, for ef_norm_mean: (0.745 -0.405 -0.505)
----analyzeAtlas elapsed time: 0.2212 seconds
Tips and Tricks
- The run function can be called with any targetStage from Stage.INIT to Stage.ATLAS. Stages that have already been completed will not be run again, and all stages that need to be completed to reach the targetStage will be completed in turn.
- IMPORTANT: To continue working with a model from a previous Matlab session, you create an EFMouse object with the dir and ID input arguments to specify the folder with the (previously saved) results and the ID of the montage. For instance, to open the simulation from the tutorial at the stage where it was last saved:
o = EFMouse(dir='/Users/rubensanchez/desktop/efmouse_sim/1xBack',ID='1xBack')
