[FieldTrip] Magnitude of leadfield in beamformer

[Jinwen Wei]

Dear all,

My name is Jinwen and I am conducting forward modelling for EEG source
reconstruction following
*https://www.fieldtriptoolbox.org/workshop/oslo2019/forward_modeling/
<https://www.fieldtriptoolbox.org/workshop/oslo2019/forward_modeling/>*. I
have a question about the magnitude of lead field matrix.

According to the tutorial, the leadfield describes what would be seen at
the sensor level given that a source was active with a given current (1
Am). In the ending part of the tutorial, a realistic source current of 100
nAm was used to plot the lead field and the resulting magnitude of lead
field was 10^-5. That is to say, the original lead field had a magnitude of
10^2 because 10^2 *100*10^-9 = 10^-5. However, how come the original lead
field has such a huge magnitude. Actually, when I modelled the lead field
using standard BEM, I found the magnitude of the original lead field was
quite small, like 10^-5. So I am wondering what magnitude of the
original lead field is.

Best regards,
Jinwen
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