Text file format when import EEG electrode positions from a file

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1

The digitization is from a Polhemus Fastrak digitizer. Nasion, LPA, RPA, and all EEG electrodes were digitized. The text file includes Polhemus coordinate data on each position from a stylus as a row and a reference sensor that's attached to the scalp as the other row. When to import EEG electrode positions from a text file, how should data be organized in this text file?

2

You can use the Polhemus file (.pos).

Once the raw (recordings) are linked to the database, right-click the channel file > Add EEG positions > Import from file The Polhemus will be an option in the Files of Type drop menu.

https://neuroimage.usc.edu/brainstorm/Tutorials/Epilepsy#Prepare_the_channel_file

3

I don't have the .pos file. I only have the .txt file.
My question is how to re-organize this .txt file so it can be correctly read in Brainstorm through "Add EEG positions"? What is the first column, the second column, etc? Does the file keep both the data from the stylus and the reference sensor? If so, How to differentiate data from the stylus and the reference sensor?
Thank you.

4

Thanks for the clarification.

Have you tried to import the .txt file with Polhemus option?
That expects a text file with four columns ('Name','X','Y','Z'), one header line and [cm] as units

Alternatively, you could write it a:

  • Format ASCII_NXYZ: four columns ('Name','X','Y','Z'), no header line and [mm] as units
  • Format ASCII_XYZN: four columns ('X','Y','Z','Name'), no header line and [mm] as units

Columns can be comma-separated or tab-separated