EEG Sensor space metrics

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Hello everyone,
I am new to this so I hope I am not bothering you with my question.
I am working with MNE Python stable version 1.6 (OS Windows10), to later use HNN core (HNN Core | HNN), to fit the data and retrieve the underlying cellular and circuit-level neural generators.
They provide one tutorial on how to fit real data (04. From MEG sensor-space data to HNN simulation — hnn-core documentation) where the final label extracted time course results to be in (n)A*m.
I was trying to do the same with my EEG data but I do not understand what units of measurements I end up with in the source space - also how this would change among the different methods used (MNE, dSPM, etc).
Can anyone help me understand this?
I read the MNE documentation on “Inverse Problem and Source Analysis” but I did not find anything so far.

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Hello and welcome to the forum!

Maybe this posting answers your question:

Best wishes,
Richard

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Thank you so much Richard.

And what about the " *meter "? Is it just a different way to say the same thing?
On the tutorial mentioned they use:

stc = apply_inverse(evoked, inv, lambda2, method='MNE',
                    pick_ori="normal", return_residual=False,
                    verbose=True)
flip_data = stc.extract_label_time_course(label_s1, inv['src'],
                                          mode='pca_flip')
dipole_tc = -flip_data[0] * 1e9

And refer to dipole_tc as [nAm].
Thank you again for your patience and for your time,
Best,

Sara

4

Whoops, you might be right! And the response I cited above might be wrong. Indeed, the unit is Ampere*meter. You can even check the unit of the inverse operator:

# %%
import mne

sample_dir = mne.datasets.sample.data_path()
inv_op_fname = sample_dir / 'MEG' / 'sample' / 'sample_audvis-eeg-oct-6-eeg-inv.fif'
inv_op = mne.minimum_norm.read_inverse_operator(inv_op_fname)
print(inv_op["units"])

Produces:

'Am'

Sorry about the confusion.

I’m not sure if the units eventually cancel out though? :smiley: @larsoner or @agramfort, this is probably something you can answer from the top of your head :slight_smile:

Best wishes,
Richard

5

Yeah the units of MNE and eLORETA should be SI Ampere-meter. And once you take that and multiple by 1e9 nAm/Am the units are in nAm, so I think the tutorial is correct. This will be the same regardless of whether you use MEG, EEG, or M/EEG data.

3 Likes
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Thank you very much to everyone

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