Display area of ECoG signals on cortex are too large


I want to display the ECoG signal on the macaque cortex. (using the anatomical dataset in the tutorial).

* I use Brainstorm standalone on Windows 10.

First, MRI data were aligned and surface data were imported according to the procedure manual.
Then, I imported my ECoG data and displayed it on the cortex with "ECoG -> display on cortex".

However, the area where the signal is displayed is too large for the electrode size.
As a test, one channel is placed at a distance from the other. You can see how large it is.

I would like the signal to be displayed on the bottom of the electrode. My vision is like this...

Can the signal spread be adjusted?
As @Francois says here, the parameter "excludeParam" probably determines the vertices to which the signal values are assigned, but is there any way to adjust this?

If < 0, exclude the vertices that are further from the absolute distance excludeParam (in millimeters)

Have you tried to change the colormap setting?

Why should the colormap setting be changed?
The issue is the area where the signal is projected onto the cortex (the number of vertices to which the signal value is assigned), not the range of the signal value.

This is not a colormap question, indeed.

The parameter excludeParam controls for the maximum distance from the center of the contact.
The default values are set in panel_surface.m, it is 15mm for ECOG:

Your screen capture confirms that your channels are not correctly configured as ECOG.
If you used "ECoG" or did not change it from the default "EEG", make sure you set all the channels to "ECOG" (all capitalized).

Rendering should look like this:

If you haven't read them yet, I recommend you follow the EEG, SEEG and ECOG tutorials before processing your own data:

Thanks for your reply.

I think I correctly set the channels as ECoG.
Here are the steps I took for the ECoG data.

First, I select "import MEG/EEG" and then import a mat file because my ECoG data is defined as a MATLAB matrix (time * channel).
Second, I set the channel type as "ECOG" according to this.
Finally, I placed the electrodes on the MRI viewer and projected them onto the surface.

I guess "excludeParam" (1.5mm) is the cause...
In the MRI data, the brain area is too small, so a large area of the cortex may be within 1.5mm.

Indeed, I had not realized that this distance of 15mm was not adapted to non-human brains.

I made this property editable. Now you can right-click on the figure > Channels > Edit interpolation distance, and set it to a lower value.


The corresponding GitHub commit: https://github.com/brainstorm-tools/brainstorm3/commit/40fd14eb0c0b404111fa2b9b93bb42fe8b4a1ecb

Update Brainstorm to get this fix.
Does it solve your problem?

Thank you for the update.

However, I have a request.
I am using the standalone version because do not have MATLAB.
Therefore, could you please compile the latest version and commit it?

Done. You can download the recompiled version from the Download page.

Note that Brainstorm is now compiled with Matlab 2022b instead of 2020a.
You'll need to install a new Matlab Runtime. See the Installation page for help:

I have confirmed that I can control the size of the projected area.

My problem has been solved.
I appreciate your quick support.