[Mne_analysis] EEG reference

[Christopher Bailey]

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<mailto: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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