[Eeglablist] segmenting resting-state EEG data to use in spectopo. Why segmenting?

[Neeraj Sharma]

Hi Ana,

May be the following can help you.
1.  Why do we average? There may be spurious activity in some segments
hence averaging several segments and obtaining the confidence interval
helps.

2. Why do we segment? Generally segmentation is done such that that there
is an event of interest in each segment, and analyzing several
event-synchronized segments helps to understand the event-evoked activity.
A simple example is by averaging the segments. In resting state EEG there
is no external event. Hence, you are free to choose segments any way. As
you are interested in alpha wave analysis so the segment duration should be
such that it covers few cycles of alpha wave (and also theta wave).

3. Should you take the whole  duration of recording as one segment? You can
but then you wont get to obtain any confidence interval (or standard
deviation) for the estimate. Any spurious activity will average out but you
will never know how frequent the spurious activity would have been.  So, in
short, better to segment in something like 1 min segments.

Cheers,
Neeraj


On Mon, Mar 2, 2020 at 6:12 PM Ana Navarro Cebrian <
anavarrocebrian at gmail.com> wrote:

> Hi all,
>
> I have two resting state sessions of 5 minutes (pre and post) that I want
> to compare with each other. I'm mostly interested in the alpha and theta
> bands. In the past I've segmented resting state EEG activity and it seems
> that, as far as I know, this is what people normally do. However, I was
> just wondering why we do this instead of analyzing the entire resting-state
> period all together. What are the benefits of segmenting resting state data
> without any stimuli or responses? Could I calculate individual alpha peak
> or just the average power using the entire period without segmenting? I'm
> using the spectopo function right now to calculate power.
>
> Thank you for any inputs!
> Ana
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