[Eeglablist] Separating out Alpha from mu oscillations

B L thirstyforknowledge123 at gmail.com
Wed Mar 26 08:30:41 PDT 2014


Thanks Dr.Makeig and Jason for your valuable comments.

I will try ICA on our dataset to see if I can successfully separate out the
influence of occipital alpha from central/frontal regions.

Bala


On Tue, Mar 25, 2014 at 5:38 PM, Scott Makeig <smakeig at ucsd.edu> wrote:

> Bala,
>
> The subject of the generators of EEG alpha/mu oscillations is a complex
> one.  Julie Onton made a poster on what ICA tells us here<http://sccn.ucsd.edu/~scott/pdf/Onton_SfN05_AlphaPosterMini.pdf>.
>  Basically, we have found no dramatic difference between motor mu
> oscillations and occipital/parietal alpha oscillations:
>
> They both have a peak near 10 Hz (in adults) - by convention in the range
> 8-12 Hz.  They both are non-sinusoidal (i.e., they have harmonics in their
> power spectra, for mu a bit more pronounced). They both separate into lower
> and higher frequency alpha processes under Independent Modulator analysis
> (as discussed here<http://sccn.ucsd.edu/~scott/pdf/Onton_CNS09_AlphaIMPoster.pdf>
> ).
>
> They are both associated with inattention (positive disregard for the
> 'receptive focus' of the cortical area --> alpha/mu flooding;  positive
> attention to the 'receptive focus' --> alpha blocking). They differ
> principally in location (alpha, across the occipital and parietal cortices;
> mu, near the somatomotor strip).
>
> Of course, at the scalp channels they are highly mixed by volume
> conduction and can only be separated by ICA, so far as I am aware.
>
> Some subsets of IC sources generating alpha band oscillations form
> (somewhat) dependent subspaces (as confirmed by pairwise mutual information
> measures, for which Jason Palmer has contributed a function in the EEGLAB
> miscfunc folder). These dependencies may index mutual influences of various
> types including (for alpha ICs with adjacent equivalent dipole locations)
> the possibility of (local) alpha traveling wave phenomena.
>
> Scott Makeig
>
>
> On Tue, Mar 25, 2014 at 6:58 AM, B L <thirstyforknowledge123 at gmail.com>wrote:
>
>> Hi,
>>
>> I guess this topic has been discussed in the past but I cant find an
>> effective solution.
>>
>> We know that, it  is very common for the alpha oscillation to have
>> influence up to almost the frontal electrodes. My question is - If we are
>> interested only in mu rhythm in a visual-motor task, what is the best way
>> to tease out the alpha activity from the motor regions so the comparison
>> across groups is more effective?
>> Will ICA work better for this(just identifying the alpha component and
>> removing it)? Is there any other method researchers commonly use for this
>> purpose?
>> Any help is much appreciated.
>>
>> Thanks!
>> Bala
>>
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>
>
>
> --
> Scott Makeig, Research Scientist and Director, Swartz Center for
> Computational Neuroscience, Institute for Neural Computation, University of
> California San Diego, La Jolla CA 92093-0961, http://sccn.ucsd.edu/~scott
>
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