Locations of electrodes F11,F12,P11,P12

Discussions
1

Hi,

I’m working with some EEG datasets that use electrode positions F11,F12,P11,P12 but I don’t have the locations for these positions. Can someone send me those locations?

The datasets have the following montage:

Number labels theta radius X Y Z sph_theta sph_phi sph_radius type urchan
21 FP2 17.9 0.515 80.8 -26.1 -4 -17.9 -2.7 85 EEG 21
22 F8 53.9 0.528 49.9 -68.4 -7.49 -53.9 -5.05 85 EEG 22
23 F12 EEG 23
24 T8 90 0.533 5.18e-015 -84.5 -8.85 -90 -5.97 85 EEG 24
25 TP10 108 0.665 -23.3 -70.1 -42.1 -108 -29.7 85 EEG 25
26 P8 126 0.528 -49.9 -68.4 -7.49 -126 -5.05 85 EEG 26
27 P12 EEG 27
28 F4 39.9 0.344 57.6 -48.1 39.9 -39.9 28 85 EEG 28
29 C4 90 0.267 3.87e-015 -63.2 56.9 -90 42 85 EEG 29
30 P4 140 0.344 -57.6 -48.1 39.9 -140 28 85 EEG 30
31 O2 162 0.515 -80.8 -26.1 -4 -162 -2.7 85 EEG 31
32 FP1 -17.9 0.515 80.8 26.1 -4 17.9 -2.7 85 EEG 32
33 F7 -53.9 0.528 49.9 68.4 -7.49 53.9 -5.06 85 EEG 33
34 F11 EEG 34
35 T7 -90 0.533 5.18e-015 84.5 -8.85 90 -5.97 85 EEG 35
36 TP9 -108 0.665 -23.3 70.1 -42.1 108 -29.7 85 EEG 36
37 P7 -126 0.528 -49.9 68.4 -7.49 126 -5.06 85 EEG 37
38 P11 EEG 38
39 C3 -90 0.267 3.87e-015 63.2 56.9 90 42 85 EEG 39
40 P3 -140 0.345 -57.6 48.2 39.9 140 28 85 EEG 40
41 O1 -162 0.515 -80.8 26.1 -4 162 -2.7 85 EEG 41

2

Hi,
The 3D positions of the electrodes are specific to your EEG acquisition system and the subject’s head. We do not provide a default setup for this EEG cap.
If you want to use standard positions for the electrodes, you should contact the customer service of the company that provided you with this EEG system, or other users of this specific system.
Francois

3

@Francois,

The thing is that we don’t use any cap, the electrodes are placed by hand. We use those positions to cover the lower head with inferior electrodes to record activity from the inferior surfaces of the brain. The reason to cover the lower head is that the application is epilepsy study (especially in patients with TLE). I’ve found the locations for all standard positions with a little search in the internet. But positions F12,F11,P11,P12 are not present in standard systems (like 10-20 or 10-10), they only are used to epilepsy study porposes and because of that I didn’t found them in the internet. That’s why I’m asking for help in this forum.

regards

4

If you are not using a tracking system to get the positions of the electrodes (eg. Isotrak Polhemus), you will have to set the positions of the missing electrodes manually. And as the positions you sent me are not in a standard coordinates system, you’ll have to do a lot of manual work…

  • Save the electrodes positions you posted previously in a file with a .ced extension (including the header line on top)
  • Fill the missing fields (positions of F11, F12…), by copying the positions of other electrodes
  • Create a protocol (Use default anatomy, Use one channel file per condition, Default anatomy: MNI Colin27)
  • Create a subject, create a condition
  • Right click on this condition > Import channel file: select file type “EEGLab”
  • Right-click on the channel file > MRI Registration > Manual EEG-MRI registration. Sorry, there is no tutorial yet to explain how this works, but it’s not that difficult.
  • Click on the “label” button to show the electrodes names
  • Then try to get something close to your real setup by using the buttons in the toolbar. Each time: click on a button in the toolbar (get the description by leaving the mouse for a while over the button), then right-click and hold the right button + move mouse up/down to apply the transformation. To guide you, the first steps will be:
    – Select “resize” button: Increase a little bit the size of the electrodes array
    – Select “Translation/Z”: move electrodes to the top of the head
    – Click on “Project electrodes on scalp surface”
    – Select “Move electrode”, select an electrode by clicking on it, right-click, hold right button, and grad the electrode to the point of the head you think it should be. Do that for each electrode, especially for the ones that are superimposed (your F11,F12,P11,P12 channels, that should be shown on top of other electrodes…)
  • Click on “Ok” when you’re done
  • Import the recordings, compute the forware/inverse models, etc. etc.

Francois

5

@Francois

Thanks a lot for your help. I did everything you said and it work perfectly.

Best regards