[Eeglablist] EEGLab trouble re-referencing my data to multiple electrodes

[Cedric Cannard]

Hi Maria,

Linked mastoids reference IS very vulnerable to dipole fluctuations, especially in the alpha band with eyes closed, there are inter-hemispheric asymmetries. See for example:
https://urldefense.com/v3/__https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6449497/https:/*pubmed.ncbi.nlm.nih.gov/11577908/__;Lw!!Mih3wA!F6a_K0IK0-8VQymoeg_VVBXnK86TR56x-ksKEZxGqf_SYITutl0GN8TktAPa1jY1Urh6KJDzqzxybPZR465_ICTodw$ 

Again, it is generally recommended to use average or infinity/REST reference if you have 64 electrodes. Average reference can easily be done in EEGLAB > Tools > Re-reference. If you can do CSD-transformation it's even better, but more challenging (requires head models, etc.).

If you want to add back your initial reference channels, you can follow these directions:
https://sccn.ucsd.edu/wiki/Makoto%27s_useful_EEGLAB_code#How_to_re-reference_to_average_potential_including_the_initial_reference_.2801.2F25.2F2022.29https://eeglab.org/tutorials/05_Preprocess/rereferencing.html#retaining-the-reference-channel

If you still want to do mastoids-reference, here are the instructions:
https://urldefense.com/v3/__https://eeglab.org/tutorials/05_Preprocess/rereferencing.html*retaining-the-reference-channel__;Iw!!Mih3wA!F6a_K0IK0-8VQymoeg_VVBXnK86TR56x-ksKEZxGqf_SYITutl0GN8TktAPa1jY1Urh6KJDzqzxybPZR467bS-BKrw$ 

Hope this helps,

Cedric Cannard

Sent with [Proton Mail](https://urldefense.com/v3/__https://proton.me/__;!!Mih3wA!F6a_K0IK0-8VQymoeg_VVBXnK86TR56x-ksKEZxGqf_SYITutl0GN8TktAPa1jY1Urh6KJDzqzxybPZR464sBxdcOw$ ) secure email.

------- Original Message -------
On Friday, May 19th, 2023 at 6:24 AM, Maria Coelho <mariapirescoelho27 at gmail.com> wrote:

> Dear Cedric,
>
> Thank you for your reply.
>
> Yes, we are using Fp1 and AF8 as references as they are not channels of interest. We chose the linked mastoid referencing for our data to avoid dipole fluctuations, as we use both earlobes as references and set both as references.
>
> Kind regards,
>
> Maria Coelho
>
> Cedric Cannard <ccannard at protonmail.com> escreveu no dia quinta, 18/05/2023 à(s) 20:20:
>
>> Dear Maria,
>>
>> Are you sure your reference labels are Fp1 and AF8? Because these are prefrontal electrodes, not earlobes. In any case, is there a rationale for using linked mastoid referencing for your data? Because if you have 64 electrodes, it is much better to re-reference to average or infinity/REST (both available in EEGLAB) than to linked mastoids, which is vulnerable to left/right dipole fluctuations.
>>
>> Cheers,
>>
>> Cedric Cannard
>>
>> Sent with Proton Mail secure email.
>>
>> ------- Original Message -------
>> On Thursday, May 18th, 2023 at 9:23 AM, Maria Coelho via eeglablist <eeglablist at sccn.ucsd.edu> wrote:
>>
>>> Hi,
>>>
>>> Firstly, thank you for the open discussion list on EEGLab matters. I am
>>> currently preprocessing my data and mailing lists like these are very
>>> useful.
>>>
>>> I am having difficulties in re-referencing my data.
>>>
>>> By default in Brain Vision Recorder, my reference channel is Fp1. When I
>>> import my .vhdr files to EEGLab interface, this channel doesn't appear in
>>> "Edit --> Channel Locations" (as I am assuming EEGlab also refers to Fp1 as
>>>
>>> my reference channel).
>>>
>>> However, I have two references, in both earlobes: Fp1 and AF8, and I need
>>> to reference my data to the mean of these two channels' data.
>>>
>>> I have checked the procedure in EEGlab Tutorial, where I can create a new
>>> channel (in Edit --> Channel Locations) in case the original reference does
>>>
>>> not appear visible, as it is the case, in Fp1 for instance. Yet, by
>>> creating Fp1 as a new channel and set it as my reference (as described in
>>> Tutorials --> Preprocess Data --> Re-referencing --> Retaining the
>>>
>>> reference channel), the new channel Fp1 does not contain its original data.
>>>
>>> With this issue, I cannot proceed to the next step, where it is described
>>> how to use two references as I wish to use (in Tutorials --> Preprocess
>>>
>>> Data --> Re-referencing --> Re-referencing to multiple electrodes).
>>>
>>>
>>> I am using the brain products 64-channel EEG system.
>>>
>>> Thank you in advance, and I hope I was clear in describing my problem.
>>> I look forward to hearing from you.
>>>
>>> Maria Coelho
>>> _______________________________________________
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