[Eeglablist] Frontal Alpha Asymmeytri Score Problem

[Cedric Cannard]

Hi,

> Many paper use F3/F4 but some use F7/F8, F5/F6 or "several frontal dipol score average" to measure FAA. How am i decide? which one?

I don't think there is a clear answer to that, to my knowledge.

According to recent studies investigating frontal alpha asymmetry with advanced methods (EEG source localization, simultaneous EEG-fMRI), the asymmetry seems to reflect activity from executive control mechanisms of the frontoparietal network, which is broad and complex. See for example: https://urldefense.com/v3/__https://canlabvuw.files.wordpress.com/2015/05/an-asymmetric-inhibition-model-of-hemispheric-differences-in-emotional-processing.pdf__;!!Mih3wA!VmV6WMTbBJy3nsZGZqCQq0xQDkTJw2TXxo7Ks-TtLnMdcEgPD9RhEcEEztISYclxjKRzxA$ 

You might get different scores because of the dipole polarity your electrodes might be picking up, depending on gyri orientation. The choice of electrode, processing methods, and electrode montage, are some of the causes of inconsistencies/contradictions in the EEG asymmetry literature. Some authors average one hemisphere, whereas some others have looked at individual electrodes. If there is an established and validated choice for your specific montage, I would use that. It could also be interesting to compare the differences in asymmetry scores between your electrodes, and with the average over the hemisphere. In theory, the difference between right/left hemisphere should be pretty consistent if it really reflects the asymmetry component of such a broad network between right and left hemispheres. If the differences between electrodes within each hemisphere are the same (e.g. between F5/F7 and F6/F8 for example), the difference across hemispheres would then be consistent.

Another gap comes from which frequencies within the alpha band you are looking at. As shown by P. Nunez (https://urldefense.com/v3/__https://www.google.com/books/edition/Electric_Fields_of_the_Brain/fUv54as56_8C?hl=en&gbpv=0__;!!Mih3wA!VmV6WMTbBJy3nsZGZqCQq0xQDkTJw2TXxo7Ks-TtLnMdcEgPD9RhEcEEztISYclr8vGVPg$ ), upper and lower alpha can have different functions and sources. So averaging the whole band when computing alpha asymmetry scores may blur things. You could check if your differences are due to that.

This is probably not making things easier for you, sorry :)

Cedric

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Monday, February 22, 2021 6:51 AM, gökhan alper figen <gokhanalper at gmail.com> wrote:

> Thanks Cedric for the answer,
> Participants watched commercial video and i collected their data by eeg. I want to measure "all time average like/unlike(pleasantness/unpleasantness) level". I found some papers for asymmetry study on my device, not necessary re-reference . But i am not sure FAA score value is true or not, because i did not see any "example value" in any paper or study.
> You sent: https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/abs/pii/S016787601630784X__;!!Mih3wA!VmV6WMTbBJy3nsZGZqCQq0xQDkTJw2TXxo7Ks-TtLnMdcEgPD9RhEcEEztISYclHn0403A$  this paper very helpful to calculate(window size, overlap etc.,sample rate) FAA.
>
> Many paper use F3/F4 but some use F7/F8, F5/F6 or "several frontal dipol score average" to measure FAA. How am i decide? which one?
> thanks again.
>
> Cedric Cannard <ccannard at protonmail.com>, 22 Şub 2021 Pzt, 09:51 tarihinde şunu yazdı:
>
>> Hi,
>>
>> I believe you don’t need to remove baseline as high pass filter does it.
>> Average-referencing is generally done before ICA yes, with different ways to avoid rank-deficiency: https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#Re-reference_the_data_to_average_.2808.2F02.2F2020_Updated.29
>>
>> https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#Re-reference_the_data_to_average_.2808.2F02.2F2020_Updated.29However, you need at least 64 channels for average reference. REST-referencing (https://urldefense.com/v3/__https://eeglab.org/tutorials/05_Preprocess/rereferencing.html__;!!Mih3wA!VmV6WMTbBJy3nsZGZqCQq0xQDkTJw2TXxo7Ks-TtLnMdcEgPD9RhEcEEztISYck8YLC4kQ$ ; bottom) can be done with at least 16 channels, not sure what happens with 14.
>> I am not aware of a paper testing it on this EEG setup. Comparing how asymmetry scores are affected by the referencing with another system with 16 channels could help.
>>
>> More info on EEG asymmetry and referencing for your other questions: https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/abs/pii/S016787601630784X__;!!Mih3wA!VmV6WMTbBJy3nsZGZqCQq0xQDkTJw2TXxo7Ks-TtLnMdcEgPD9RhEcEEztISYclHn0403A$ 
>>
>> https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/abs/pii/S016787601630784XC**Adric__;w6k!!Mih3wA!VmV6WMTbBJy3nsZGZqCQq0xQDkTJw2TXxo7Ks-TtLnMdcEgPD9RhEcEEztISYckdCYlN7w$ 
>>
>> On Sat, Feb 20, 2021 at 05:28, gökhan alper figen <gokhanalper at gmail.com> wrote:
>>
>>> Hi everyone,
>>> i have phd project. My eeg device is emotiv epoc + 14 channel.
>>> I applied on EEGLAB for raw egg preprocess:
>>> 1-remove baseline(for time)
>>> 2-select channel
>>> 3-load channel location
>>> 4-remove epoch baseline(DCOFF)
>>> 5-1-45 Hz Fır-filter
>>> 6-???? i dont apply re-reference. Because my device reference is
>>> Mastoid(P3-P4). But i am not sure for this step. I tried
>>> re-reference(average), but this time ICA calculate one a component is under
>>> calculated. HELP ME. Is it necessary to re-reference?
>>> 7- ICA
>>> 8-Remove for Artifact applied ADJUST
>>> 9- Last one on matlab, i applied frontal alpha asymmetry algorithm(8-13Hz).
>>> But i have got another problem in here. I got AF3-AF4, F7-F8, F3-F4,
>>> FC5-FC6 dipole electrode on frontal lobe. Which dipole is important frontal
>>> alpha asymmetry? Used one by one at different times in the literature.İn
>>> addition i have different score same trial(for example: AF3-AF4-->positive,
>>> F7-F8--> negative, F3-F4-->positive, FC5-FC6-->negative ). is it possible?
>>>
>>> FAA SCORE:
>>> AF4-AF3 F8-F7 F4-F3 FC6-FC5 MeanFAA
>>> 0,835219 1,803982 0,768355 1,929266 1,334206
>>> 1,552542 0,523332 1,283658 0,662677 1,005552
>>> 0,212559 0,767369 -0,09146 0,533678 0,355537
>>> 2,695686 0,651778 0,208955 1,1194 1,168955
>>> 0,021023 0,745326 0,28 1,529339 0,643922
>>> 0,400539 0,693247 0,435739 1,952571 0,870524
>>> 0,069624 0,294606 1,358425 0,82884 0,637874
>>> 0,646927 0,528689 0,728926 1,521723 0,856566
>>> 0,260962 -0,12185 1,093646 1,173347 0,601527
>>> 1,228531 1,233191 1,044209 1,793257 1,324797
>>> 0,020307 0,647727 1,570798 1,414552 0,913346
>>> -0,58441 0,484781 0,804384 1,398788 0,525887
>>> 1,199436 1,282988 0,766968 1,721898 1,242822
>>> -0,2001 -0,69111 0,976038 1,513998 0,399708
>>> 0,184563 1,183316 1,678075 2,736944 1,445725
>>> -0,10969 0,93127 0,343262 0,51734 0,420546
>>> -0,22403 0,445983 -0,2119 0,763368 0,193354
>>>
>>> thanks
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