mne.create_default_subject(mne_root=None, fs_home=None, update=False, subjects_dir=None)

Create an average brain subject for subjects without structural MRI

Create a copy of fsaverage from the Freesurfer directory in subjects_dir and add auxiliary files from the mne package.


mne_root : None | str

The mne root directory (only needed if MNE_ROOT is not specified as environment variable).

fs_home : None | str

The freesurfer home directory (only needed if FREESURFER_HOME is not specified as environment variable).

update : bool

In cases where a copy of the fsaverage brain already exists in the subjects_dir, this option allows to only copy files that don’t already exist in the fsaverage directory.

subjects_dir : None | str

Override the SUBJECTS_DIR environment variable (os.environ[‘SUBJECTS_DIR’]) as destination for the new subject.


When no structural MRI is available for a subject, an average brain can be substituted. Freesurfer comes with such an average brain model, and MNE comes with some auxiliary files which make coregistration easier. create_default_subject() copies the relevant files from Freesurfer into the current subjects_dir, and also adds the auxiliary files provided by MNE.

The files provided by MNE are listed below and can be found under share/mne/mne_analyze/fsaverage in the MNE directory (see MNE manual section 7.19 Working with the average brain):

The approximate head surface triangulation for fsaverage.
The approximate inner skull surface for fsaverage.
The locations of the fiducial points (LPA, RPA, and nasion).
Contains a default MEG-MRI coordinate transformation suitable for fsaverage.