I am using brainstorm (15.06.15 version) on MATLAB 2012 (64 bt version), to digitize electrode positions with the EEG montage: GSN-hydrocel-129, fastrak, polhemus.
At the second click to the right fiducial the following error message occurs, instead of the head shape, and digitization cannot continue:
Error using view_headpoints (line 52)
No scalp surface available for this suject.
Error in panel_digitize>CreateHeadpointsFigure (line 955)
[hFig, iDS] =
view_headpoints(file_fullpath(sStudy.Channel.FileName));
Error in panel_digitize>BytesAvailable_Callback (line 1529)
CreateHeadpointsFigure();
Error in instrcb (line 36)
feval(val{1}, obj, eventStruct, val{2:end});
Warning: The BytesAvailableFcn is being disabled. To enable the
callback property
either connect to the hardware with FOPEN or set the
BytesAvailableFcn property.
In the Brainstorm database explorer, right-click on the subject folder > Edit subject.
Then change the option selected for the default anatomy to: “Yes, use protocol’s default anatomy”.
(or import the anatomy of the subject if you have it)
Thanks Francois, that worked. The only problem I seem to be having now is that the fiducials appear too far inside the grey head-shape. The electrode positions seem to lay-down fine though. Would that just be a positioning problem of the transmitter?
If you are using the default anatomy, this is using a template from the MNI (Colin27 or ICBM152). These heads are probably larger than the head of most of your subjects, and obviously don’t have the same shape. This could explain the mismatch you are observing.
In the case of a standard anatomy, do not use the menu “Refine registration using headpoints”.
More information: http://neuroimage.usc.edu/brainstorm/Tutorials/ChannelFile
If you are using an individual anatomy and don’t understand if your results are correct, please post a screen capture of the registration.
The template “Colin27” represents a man with a large head.
For any subject who has a smaller head, you will see the digitized electrodes positions inside the head.
For the estimation of the forward model, you should have the electrodes at the surface of the skin, not inside the brain volume. You have two options for fixing this:
Project the electrodes on the Colin27 scalp (right-click on the channel file > MRI Registration > Edit, then click on the project button), but in this case, you could event use a standard set of positions, you’re not going to gain much with the individual electrodes positions.