[Mne_analysis] EEG reference

[Liu Mengting]

Hi Chris,

Thanks for the info, this really helps in understanding the whole
procedures. So as I understand, reference is only a required step for
source localization, but not any other steps like measuring the
connectivity between brain regions. Sounds reference removed the DC
componets but remains the oscillation. If so, does it influence the power
in DC components? Also, does it matter the conventional source localization
methods such as dipole fitting?

Really appreciate for help,

Mengting

2017-09-25 4:55 GMT-04:00 Christopher Bailey <cjb at cfin.au.dk>:

> Hi Mengting,
>
> The average reference is the only valid scheme when performing ‘source
> localisation’, no matter what you do afterwards. To first order, the
> localisation procedure is
>
> - have measured (EEG) data
> - build forward model that computes sensor-level readings for know sources
> - compare measured and predicted (forward-projected) data to each other
> - minimise prediction error under chosen prior/model
>
> The predicted data are calculated relative to a hypothetical absolute
> reference potential of zero at infinity, whereas a real dataset could be
> referenced to a number of points on the head. To be able to compare the two
> datasets, both are re-referenced to their respective average: the average
> reference *does not depend on the location of the on-line reference
> electrode* (as long as it was functioning properly). After this
> re-scaling, the values can be compared directly.
>
> Note that like any (proper) re-referencing procedure, taking the common
> average only shifts the zero-point; relative differences between electrode
> readings remain unaltered.
>
> /Chris
>
> On 24 Sep 2017, at 01.28, Liu Mengting <bigting84 at gmail.com> wrote:
>
> Hello MNE users,
>
> I noticed that in MNE inverse operations, all EEG data were forced by an
> average referencing.
> Does anyone has insight about how does the average reference influence the
> inverse operations in MNE (I mean use dSPM or sLoreta)? Especially would
> this average referencing influence functional connectivity measure in
> source space (e.g. using phase locking)?
>
> Thanks,
> Mengting
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