EEG channel file generated from EEGLAB putting electrodes inside skull

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1

Hello,

I am attempting to import an EEG channel file created using EEGLAB. The company that created the cap used in the intervention did not provide a location file, so I created one using EEGLAB function look up locs. However, when this channel file is imported to Brainstorm, it suggests a scaling factor of 0.01, which place all the electrodes well inside the scalp, too far inside to project to the scalp with accuracy. Selecting 0.1 as the scaling factor places the electrodes very far away from the scalp. I've pasted the location file below. Does anyone have any suggestions for fixing the location file?

Number labels type theta radius X Y Z sph_theta sph_phi sph_radius
1 Fp1 -17.9 0.515 80.8 26.1 -4 17.9 -2.7 85
2 Fpz 0 0.507 85 -0 -1.79 -0 -1.2 85
3 Fp2 17.9 0.515 80.8 -26.1 -4 -17.9 -2.7 85
4 F7 -53.9 0.528 49.9 68.4 -7.49 53.9 -5.06 85
5 F3 -39.9 0.345 57.6 48.2 39.9 39.9 28 85
6 Fz 0 0.253 60.7 -0 59.5 -0 44.4 85
7 F4 39.9 0.344 57.6 -48.1 39.9 -39.9 28 85
8 F8 53.9 0.528 49.9 -68.4 -7.49 -53.9 -5.05 85
9 FC5 -69.3 0.408 28.8 76.2 24.2 69.3 16.5 85
10 FC1 -44.9 0.181 32.4 32.4 71.6 44.9 57.4 85
11 FC2 44.9 0.181 32.4 -32.4 71.6 -44.9 57.4 85
12 FC6 69.3 0.408 28.8 -76.2 24.2 -69.3 16.5 85
13 M1 -100 0.747 -11 59.6 -59.6 100 -44.5 85
14 T7 -90 0.533 5.18e-15 84.5 -8.85 90 -5.97 85
15 C3 -90 0.267 3.87e-15 63.2 56.9 90 42 85
16 Cz 0 0 5.2e-15 -0 85 -0 90 85
17 C4 90 0.267 3.87e-15 -63.2 56.9 -90 42 85
18 T8 90 0.533 5.18e-15 -84.5 -8.85 -90 -5.97 85
19 M2 100 0.747 -11 -59.6 -59.6 -100 -44.5 85
20 CP5 -111 0.408 -28.8 76.2 24.2 111 16.5 85
21 CP1 -135 0.181 -32.4 32.4 71.6 135 57.4 85
22 CP2 135 0.181 -32.4 -32.4 71.6 -135 57.4 85
23 CP6 111 0.408 -28.8 -76.2 24.2 -111 16.5 85
24 P7 -126 0.528 -49.9 68.4 -7.49 126 -5.06 85
25 P3 -140 0.345 -57.6 48.2 39.9 140 28 85
26 Pz 180 0.253 -60.7 -7.44e-15 59.5 -180 44.4 85
27 P4 140 0.344 -57.6 -48.1 39.9 -140 28 85
28 P8 126 0.528 -49.9 -68.4 -7.49 -126 -5.05 85
29 POz 180 0.38 -79 -9.68e-15 31.3 -180 21.6 85
30 O1 -162 0.515 -80.8 26.1 -4 162 -2.7 85
31 Oz 180 0.507 -85 -1.04e-14 -1.79 -180 -1.2 85
32 O2 162 0.515 -80.8 -26.1 -4 -162 -2.7 85
33 AF7 -35.9 0.522 68.7 49.7 -5.96 35.9 -4.02 85
34 AF3 -22.5 0.421 76.2 31.5 20.8 22.5 14.2 85
35 AF4 22.5 0.421 76.2 -31.5 20.8 -22.5 14.2 85
36 AF8 35.9 0.522 68.7 -49.7 -5.95 -35.9 -4.02 85
37 F5 -49.4 0.432 54 63.1 18.1 49.4 12.3 85
38 F1 -23.5 0.279 59.9 26 54.4 23.5 39.8 85
39 F2 23.5 0.279 59.9 -26 54.4 -23.5 39.8 85
40 F6 49.4 0.431 54 -63 18.2 -49.4 12.4 85
41 FC3 -62.4 0.288 31 59.3 52.5 62.4 38.1 85
42 FCz 0 0.127 32.9 -0 78.4 -0 67.2 85
43 FC4 62.4 0.288 31 -59.3 52.5 -62.4 38.1 85
44 C5 -90 0.4 4.95e-15 80.8 26.3 90 18 85
45 C1 -90 0.133 2.11e-15 34.5 77.7 90 66 85
46 C2 90 0.133 2.12e-15 -34.6 77.6 -90 66 85
47 C6 90 0.4 4.95e-15 -80.8 26.3 -90 18 85
48 CP3 -118 0.288 -31 59.3 52.5 118 38.1 85
49 CPz 180 0.127 -32.9 -4.03e-15 78.4 -180 67.2 85
50 CP4 118 0.288 -31 -59.3 52.5 -118 38.1 85
51 P5 -131 0.432 -54 63.1 18.1 131 12.3 85
52 P1 -157 0.279 -59.9 26 54.4 157 39.8 85
53 P2 157 0.279 -59.9 -26 54.4 -157 39.8 85
54 P6 131 0.431 -54 -63 18.2 -131 12.4 85
55 PO5 -149 0.466 -72.8 43 8.93 149 6.03 85
56 PO3 -158 0.421 -76.2 31.5 20.8 158 14.2 85
57 PO4 158 0.421 -76.2 -31.5 20.8 -158 14.2 85
58 PO6 149 0.466 -72.8 -43 8.93 -149 6.03 85
59 FT7 -71.9 0.532 26.2 80.4 -8.51 71.9 -5.75 85
60 FT8 71.9 0.532 26.2 -80.4 -8.51 -71.9 -5.75 85
61 TP7 -108 0.532 -26.2 80.4 -8.51 108 -5.75 85
62 TP8 108 0.532 -26.3 -80.4 -8.51 -108 -5.74 85
63 PO7 -144 0.522 -68.7 49.7 -5.96 144 -4.02 85
64 PO8 144 0.522 -68.7 -49.7 -5.95 -144 -4.02 85

2

What you have in this file are not real 3D positions, they are normalized spherical positions.
They can be used only for 2D disc/3D sphere topography display, not for anything that requires realistic spatial information.

You can do edit these default positions for your subject's anatomy:

  • Select the default scaling (0.01)
  • Right-click on the channel file > MRI registration > Edit
  • Use all the buttons in the toolbar to find an acceptable size/alignment (read the tooltips for help)
  • Project the electrodes on the head
  • Refine electrodes' positions one by one
  • Click on the OK button in the toolbar when you're done. Answer yes to confirm the modifications.

This is what we had to do with some of the templates we have available in Brainstorm, because most EEG caps manufacturers don't provide any realistic 3D positions.