[Eeglablist] EEGLAB preprocessing for sleep EEG data

[Armand Mensen]

Hi Rob,

Just a quick note. If electrodes have been changed (gel re-applied as you
said), then this will create a split in your ICs at those times since the
data, and make it hard to figure out where things are coming from. Given
you "only" have 29 channel data, this will probably lead to a poor ICA
decomposition.

Moreover, sleep data doesn't tend to decompose well into separate ICs the
first place since each slow wave or sleep spindle will be measured on
different scalp locations with different temporal properties each time. So
you actually have a separate "source" for each slow wave and spindle and
its unclear how ICA could properly combine these into a single (or a few)
components. So you already know from theory, that your largest EEG
activities (slow waves) will have a different source each time... and since
you have more than 29 slow waves... then IC will not be able to isolate
each one (but will try and fail).

Perhaps the ICA will seem to produce some ICs that look more like muscle
activity (big maybe), but I'd be suspicious that these aren't actually also
heavily mixed with neural activity of interest and ICA will just bias your
results in a way that you cannot predict, or even really account for after
you've finished.

Apologies for the pessimism but this is after seeing this sort of thing
over and over again using high-quality data from 256 channel recordings
over a whole night (NREM extracted).

Good luck!
Armand Mensen

*Postdoctoral Researcher*
*Inselspital Bern*


> ---------- Forwarded message ----------
> From: Tarik S Bel-Bahar <tarikbelbahar at gmail.com>
> To: EEGLAB User <eeglabuser at gmail.com>
> Cc: eeglablist <eeglablist at sccn.ucsd.edu>
> Bcc:
> Date: Mon, 14 Aug 2017 14:51:23 -0400
> Subject: Re: [Eeglablist] EEGLAB preprocessing for sleep EEG data
> ​Hello, brief notes below:
>
> you can put all the data from one session into ICA, after appropriately
> pre-processing the data to remove big artifacts that ICA does not like. The
> boundary events are no problem, as ICA in eeglab mixes up all data points,
> and is focused primarily on spatial patterns.
>
> Regarding your events, and 1-2 minutes of data before each event: This
> seems like very short periods and would likely lead to a not-that-great ICA
> solution. I would say worry about that after you've achieved ICA solutions
> for each subject, using as much clean data as you have for each participant.
> ​
>
> On Tue, Aug 1, 2017 at 11:32 PM, EEGLAB User <eeglabuser at gmail.com> wrote:
>
>> I have a 29-channel EEG data from overnight sleep recordings (~8 hours of
>> EEG data). The EEG data is not continuous as I have paused it if the
>> subject needed a loo break (~5-10 minutes) or to check the impedance (~2
>> minutes). This inserts a ‘boundary event’ in my EEG data. On some
>> occasions, I have also reapplied a couple of electrodes if the impedance
>> was high. In addition, sometimes I have had to stop the EEG recording and
>> start again due to some technical reasons, because of which I have two EEG
>> files for the same subject during the same night i.e. same session.
>>
>>
>> In my experiment, I have 15-20 events overnight and plan to use 1-2
>> minute data before each event for preprocessing and analyses. I would like
>> to use ICA to correct for artifacts but before I do that, I would like to
>> know if I need to split the data at each ‘boundary event’ and process them
>> as separate EEG files? Or can I just consider the EEG recording from each
>> subject as a single EEG recording and perform ICA (I can append the EEG
>> files in cases where I have two EEG files per subject in the same session)?
>> Any suggestions will be highly appreciated as I am very new to EEG and
>> MATLAB.
>>
>>
>> Thanks!
>>
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