I see that the the default ecog/seeg montages utilize a ‘local average reference’.
Any papers/theory justifying this? And wouldn’t this be a problem with an electrode that contains many contacts if interest?
Thanks.
Hello,
The default montage is named “orig” and does not re-reference your data, it shows directly the values saved in the file.
If you change the montage, close the viewer and re-open the file, it will probably use the last montage you used (making it “your” default).
The type of montage used to represent the EEG and intra-cranial recordings depends on the local routine. Original signals, bipolar montages, global or local average references, they all represent the same data in different ways. If labeled SEEG as channel type, the local avg ref is calculated only over a limited range of contacts (only one electrode, or one grid for ECOG).
John Mosher says Europeans tend to use more the average reference than Americans.
What matters is how you and your colleagues prefer looking at the signals, and how you have more experience looking at them.
I don’t know if there are publications explaining how the choice of the referencing system influences the interpretation of the data.
Francois
Hi!
Just a clarification : I think John Mosher meant that Europeans tends to use average reference for [B]EEG[/B] signals.
Regarding SEEG signals, in Marseille, we typically use NOT re-referenced montage (during recording reference is usually a subcutaneous electrode placed in Cz) or bipolar montage to explore the signals.
Some of these montage aspects are addressed in a recent Neuroimage paper by Manuel Mercier et al. (2017) “[I]Evaluation of cortical local field potential diffusion in stereotactic electro-encephalography recordings: A glimpse on white matter signal.[/I]”
I hope that it helps!
Cheers.
AnneSo
FYI: We improved significantly the tools available in Brainstorm for processing and visualizing SEEG and ECOG data, including new options for volume coregistration. They are now documented in a new tutorial:
http://neuroimage.usc.edu/brainstorm/Tutorials/Epileptogenicity