Process EEG data (new brainstormer!)

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1

Hello,

I have three .edf EEG files I am trying to analyze / visualize. I spliced together a neurocap and the wireless part of the Emotiv headset. A few of the cap placements are different than the Emotiv setup and there are only 14 channels. I am trying to figure out how to make my own cap. I tried just using the 16 electrode biosemi cap but got a sensor number mismatch error. I figured out how to edit the file but can’t figure out how to delete entries. Do I have to do that in the code?

Thank you!

2

Hi Anna,

Another tutorial you could follow to help you here is the EEG/epilepsy tutorial:
http://neuroimage.usc.edu/brainstorm/Tutorials/Epilepsy

If you have access to a Polhemus device, you could use Brainstorm to drive it (but I guess you don’t if not you would already have to channel file):
http://neuroimage.usc.edu/brainstorm/Tutorials/TutDigitize

In your case, you have to do more manual work because you don’t have the digitized positions of the electrodes.
So you have to build a correct channel file that identifies the channel names and positions correctly the electrodes on the head of the subject.
The entries in the channel file (field .Channel) are matching one-to-one the rows in the imported data matrices (.F).
You have to check carefully that the order of the channels is exactly the same in the two files. If there is the correct number of channels and they have the correct names but in a different order, nothing is going to work.

You have different options to create this channel file:

  • If you know the positions of the electrodes you want to use, create a text file with one sensor per line “channel_name X Y Z” and import it using the menu Import channel file > Format: “ASCII: Name,XYZ”
  • You can start from a default cap (as you did) then editing it first:
    • graphically to get the correct number of electrodes and correct positions (right-click on the channel file > MRI registration > Edit) => read the tool tips of all the buttons to see what they are doing
    • then change the order of the channels and their names to match the recordings (right-click on the channel file > Edit channel)
  • If you’re comfortable with manipulating Matlab structure, do this last step from your command line: right-click on the channel file > File > Export to Matlab, modify it, right-click again > File > Import from Matlab.

Let me know if you need further explanations.
Francois