[FieldTrip] add channels on an existing template for EEG layout

mikkelcv at drcmr.dk mikkelcv at drcmr.dk
Wed Apr 27 13:48:38 CEST 2022

Dear Anna-Marie

If your EEG layout is standard 10-20, you can use the EEG1020.lay or EEG1010.lay template layout files. When you  plot data, it will only use the channels that are in your data. It does not matter that the template has more names. It will include the channels you have in your data, but not the extra channels in the layout.

You create the layout for your data with ft_prepare_layout, like this:

cfg = []
cfg.layout = ‘eeg1010.lay’ % for example
myLayout = ft_prepare_layout(cfg, myData)

The output should be the layout of for your specific setup. However, if the extra channels (AFz, PO9, etc) are channels you want to remove from your data, you need to use ft_selectdata to remove them.

To restore the time course of the reference electrode, you need to do this while you re-reference the EEG data. The reference is usually not saved in the EEG files as it per definition is zero. But since referencing is a linear operation, it is easy to “restore” the activity at the reference site. It is explained in details in this tutorial: https://www.fieldtriptoolbox.org/example/rereference/. You cannot do that for the ground electrode though.

Best regards

Fra: fieldtrip <fieldtrip-bounces at science.ru.nl> på vegne af Anna-Maria via fieldtrip <fieldtrip at science.ru.nl>
Dato: onsdag, 27. april 2022 kl. 13.19
Til: fieldtrip at science.ru.nl <fieldtrip at science.ru.nl>
Cc: Strinzel at students.uni-marburg.de <Strinzel at students.uni-marburg.de>
Emne: [FieldTrip] add channels on an existing template for EEG layout

Hello everyone,

I am using FieldTrip to analyse my EEG data recorded with a Brain
Products system. I recorded EEG data from 32 electrodes (Fp1, Fp2, F7,
F3, Fz, F4, F8, FT9, Fc5, Fc1, Fc2, Fc6, FT10, T7, C3, Cz, C4, T8,
TP9, Cp5, Cp1, Cp2, Cp6, TP10, P7, P3, Pz, P4, P8, and Oz, plus 2
ocular electrodes (O1 and O2), according to the extended 10/20
international system) with ground located between Fp1 and Fp2 and
reference electrode located on FCz.
I can't find a layout like discribed above on the fieldtrip webpage
http://fieldtrip.fcdonders.nl/template/layout but I know that
fieldtrip also provide the possibility to prepare a layout with the
ft_prepare_layout  function.

How can I add channels on an already existing template like the
easycapM23.mat template?
I want to add Oz and the ground, and reference electrode and I want to
remove the following channels: AFz, PO9, O1, O1, PO10.


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