[FieldTrip] Scaling of Laplacian transformed ERPs

Schoffelen, J.M. (Jan Mathijs) jan.schoffelen at donders.ru.nl
Mon May 17 11:02:15 CEST 2021

Hi Tasha,

Since you are referring to FieldTrip as a plug-in to Brainstorm, it is not clear to us whether you are using (possibly outdated) fieldtrip code that comes shipped with Brainstorm, or whether you have computed the spatial derivatives in ‘plain’ up-to-date FieldTrip.

Hence, it is unclear what algorithm was used for the Laplacian, so it’s hard to comment about units to begin with. Also, since you are visualizing in Brainstorm, it’s Brainstorm that seems to interpret (and perhaps rescales) the numeric data and adds a unit-label to the ERP’s y-axis, so perhaps it’s better to ask your question to  François and his team.

Best wishes,

On 14 May 2021, at 14:21, Natalie Poppa <Natalie.Poppa at UGent.be<mailto:Natalie.Poppa at UGent.be>> wrote:


I was using the Fieldtrip plug-in within Brainstorm to apply the Laplacian spline transformation to my ERPs. When I visualized ERPs within Brainstorm, they were scaled approximately between -150 to 150 (the units were labeled microvolts, but this must be a mislabeling since it should be in V/m^2)... Anyway, when I export my ERPs, the values are 10^6 times smaller. Should I rescale them to match what I see when plotting in Brainstorm, or is V/m^2 expected to be a very small number?

Thank you,


Tasha Poppa, PhD
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