[Eeglablist] Dipolar components

[Makoto Miyakoshi]

Dear Ali,

> So does it mean that the appearance of the scalp maps does not have any
relationship with the dipolarity? (i.e. can we judge/guess from the
appearance of a scalp maps that it could be a dipolar source? )

Dipolarity is directly determined by scalp topography. I can almost predict
where dipoles should be fit when I see the IC scalp maps, if they are
dipolar. It's a very simple thing.

> However, dipoles may invert when neurons fire, so the EEG sources can't
be stationary. So how is this assumption plausible for the constitutive
sources of EEG data?

As EEG is an AC signal, by definition polarity must invert (a lot), which
is NOT a cause of spatial non-stationarity. Do you have a speaker with a
bass-reflex port in the back side? Or even better, do you own Magnepan,
Martin Logan, Apogee, Quad, or old STAX? These speakers are dipolar, but
they don't run around the room.

Makoto



On Thu, Feb 2, 2017 at 10:33 AM, ali zahedi <ali.zahedi.bham at gmail.com>
wrote:

> Dear Makoto,
>
> Thank you for your explanation.
> So does it mean that the appearance of the scalp maps does not have any
> relationship with the dipolarity? (i.e. can we judge/guess from the
> appearance of a scalp maps that it could be a dipolar source? )
>
> Also, as it mentioned in Delorme et al. (2012) PLoS One paper "The
> motivation for the dipolarity is the assumption that brain and non-brain
> EEG sources have spatially fixed source locations and orientations".
> However, dipoles may invert when neurons fire, so the EEG sources can't be
> stationary. So how is this assumption plausible for the constitutive
> sources of EEG data?
>
> Regards,
> Ali
>
>
> On Thu, Feb 2, 2017 at 2:55 AM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> wrote:
>
>> Dear Ali,
>>
>> The scalp maps of ICs directly reflects the columns of mixing matrix
>> (i.e. EEG.icawinv).
>> See slide 14: 'How does ICA model physiology' (from EEGLAB workshop 2017
>> at Mysore)
>> https://sccn.ucsd.edu/mediawiki/images/7/74/IcaDecomposition
>> OfEegData4.pdf
>>
>> Therefore, if you see nice dipolar scalp maps, it means that ICA (which
>> does not know anything... it does not know channel locations, does not even
>> know the signal is EEG!) identified theoretical electrophysiological
>> property of EEG (see Nunes books about it).
>>
>> > Is it just the smoothness of the scalp maps that determines capacity to
>> fit dipoles?
>>
>> No, not the smoothness. It's dipolarity. See Delorme et al. (2012) PLoS
>> One paper.
>>
>> Makoto
>>
>> On Sat, Jan 28, 2017 at 12:00 PM, ali zahedi <ali.zahedi.bham at gmail.com>
>> wrote:
>>
>>> Dear all,
>>>
>>> Regarding the dipole fitting to the ICs and dipolar components, what are
>>> the properties of the scalp maps of the ICs that can fit with a dipole with
>>> less than a residual variance? Is it just the smoothness of the scalp maps
>>> that determines capacity to fit dipoles?
>>>
>>> I really appreciate it if you could help me with this.
>>>
>>> Regards,
>>> Ali
>>>
>>> _______________________________________________
>>> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
>>> To unsubscribe, send an empty email to eeglablist-unsubscribe at sccn.uc
>>> sd.edu
>>> For digest mode, send an email with the subject "set digest mime" to
>>> eeglablist-request at sccn.ucsd.edu
>>>
>>
>>
>>
>> --
>> Makoto Miyakoshi
>> Swartz Center for Computational Neuroscience
>> Institute for Neural Computation, University of California San Diego
>>
>
>


-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20170202/e5a6be1f/attachment.html>