default MEG/EEG layout and montage alignment

💬 Support & Discussions
1

Hello everyone,

I would like to examine how the CTF-275 layout or montage aligns with EEG. However, I have encountered a few issues:

  1. I seem to have not found the default CTF-275 montage.
  2. I would also like to ask whether the default unit-normalized positions of the channels in 2D are the same for MEG and EEG. It seems a bit strange to me because, based on the default layout in MNE, if I could easily align the MEG layout to the EEG layout, the outermost MEG points are generally located between AFz and Fz. Is this True?

Any help would be appreciated!

Additional information:

Code provided:
layout = mne.channels.read_layout(‘CTF275’, scale=1) # Load the CTF 275 layout
layout.plot() # Plot the layout

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The outermost MEG channel is MZF01, whose y position is 0.90, between Fz(0.79) and AFz(1.18)

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2

Layouts are used for 2D visualization purposes, you want to take a look at montages, which contain actual (or template) 2D or 3D locations. See e.g. Glossary — MNE 1.6.1 documentation.

3

Thank you for your response. I have searched for the default montage for EEG, but I couldn’t find the ctf-275 montage. Could you please advise me on how to search for the ctf-275 montage and then to register it with the EEG channels’ positions? Your guidance would be greatly appreciated:)

4

After reading your initial question again, maybe you do not need 3D locations if you are only interested in how MEG and EEG locations align on a 2D projected head surface, so you can probably stick with layouts. MNE-Python ships a EEG1005 layout, which contains the standard 10-05 electrode locations.

5

I apologize for any confusion in my previous message. I have indeed found the layout for EEG1005, and I am now looking to compare it with the layout for ctf-275. I noticed that the outermost channels in the ctf layout seem to be positioned between the Fz and FCz channels in the EEG layout. As I am new to MEG and unfamiliar with this setup, I would like to kindly ask if this positioning is correct.

6

Maybe someone with experience in both MEG and EEG can chime in? Unfortunately, I am not familiar with MEG, so I cannot answer your question.

7

you can do something like this:

import matplotlib.pyplot as plt
import mne
from mne.datasets.sample import data_path
from mne.viz.topomap import _prepare_topomap_plot

# Load the data
data_path = data_path()
evoked = mne.read_evokeds(data_path / "MEG/sample/sample_audvis-ave.fif")[0]

for ch_type in ["eeg", "mag"]:
    sphere = None
    (
        picks,
        pos,
        merge_channels,
        names,
        ch_type,
        sphere,
        clip_origin,
    ) = _prepare_topomap_plot(evoked, ch_type, sphere=sphere)

    plt.scatter(pos[:, 0], pos[:, 1], s=30, vmin=-1, vmax=1, label=ch_type)

plt.legend()
1 Like
9

Although the issue was not resolved, I truly appreciate your response：）

11

Thank you for your response. I have tested your method using a CTF dataset, and it did yield results. However, I find it a bit peculiar that the Fpz point in the EEG channels is located within the MEG channels. It seems like the MEG layout is relatively larger compared to the EEG layout. Maybe their coordinate systems are different. I am uncertain if this alignment accurately represents the real situation.

This is the result of the ctf file, which has 274 MEG channels and 64 EEG channels

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