FreeSurfer average template (fsaverage)

Description

TODO(confirm) — the author’s catalog does not hold this dataset (§10.1 rule 3); this page carries only the §10.2 facts until a registry stub is added (§10.11 item 8).

Curriculum role: Template anatomy for forward models (§10.2): surfaces, volumes, parcellations, and — in MNE’s copy — a head surface, fiducials, a head-to-MRI transform and 1- and 3-layer BEM surfaces and solutions

Citation

• Paper DOI: TODO(confirm)
• Dataset DOI: TODO(confirm)
• Reference: TODO(confirm) — neither FreeSurfer’s FsAverage wiki page nor MNE-Python’s fsaverage documentation states a citation to use for the template. The spherical-averaging method behind it is usually cited as Fischl, B., Sereno, M. I., Tootell, R. B. H., & Dale, A. M. (1999). High-resolution intersubject averaging and a coordinate system for the cortical surface. Human Brain Mapping, 8(4), 272-284, doi:10.1002/(SICI)1097-0193(1999)8:4<272::AID-HBM10>3.0.CO;2-4 (DOI verified via Crossref and against MNE’s own references.bib entry FischlEtAl1999a on 2026-09-18) — but no primary source read here says that this is the citation fsaverage itself asks for.

Download and access

Field	Value
Official source	https://surfer.nmr.mgh.harvard.edu/fswiki/FsAverage
Access class	registration
Size	195,753,120 bytes (root.zip) + 238,821,363 bytes (bem.zip) = 434,574,483 bytes compressed for MNE’s copy; about 760 MB once extracted
Format	freesurfer, fif
BIDS	false
Mirrors	Ships inside the FreeSurfer distribution at $FREESURFER_HOME/subjects/fsaverage (FreeSurfer FsAverage wiki: ‘it can be found in the distribution itself’); MNE-Python’s copy, the one mne.datasets.fetch_fsaverage() downloads: OSF node rxvq7, root.zip (file GUID 3bxqt, 195,753,120 bytes) and bem.zip (GUID 7ve8g, 238,821,363 bytes)

Access steps:

1. Canonical route — FreeSurfer’s own DownloadAndInstall page, read 2026-09-18: ‘A license key must be obtained to make the FreeSurfer tools operational. Obtaining a license is free and comes in the form of a license.txt file. Once you obtain the license.txt key file, copy it to your FreeSurfer installation directory.’ fsaverage ships inside that distribution.
2. MNE route — mne.datasets.fetch_fsaverage() downloads MNE’s copy from OSF with no registration, no licence key and no click-through. The two channels disagree about what obtaining this data requires; §10.7’s most-restrictive rule puts access at ‘registration’.

License

• Name: FreeSurfer-Software-License-1.0
• Note (verbatim from the directory): SETTLED, and it does not qualify. The governing licence is the FreeSurfer Software License Agreement, Version 1.0, February 2011 (surfer.nmr.mgh.harvard.edu/fswiki/FreeSurferSoftwareLicense, read in full 2026-09-18). It covers data, not only code: ‘Part B of this Agreement applies to downloads of software and/or data from FreeSurfer’, and ‘If you distribute Software (as defined below) downloaded from FreeSurfer, all of the paragraphs of Part B of this Agreement must be included with and apply to such Software.’ Part B grants ‘a royalty-free, non-exclusive license to use, reproduce, make derivative works of, display and distribute the Software, provided that: … (b) in connection with any copy of or sublicense of all or any portion of the Software, all of the terms and conditions in this Software License shall appear in and shall apply to such copy and such sublicense, including without limitation all source and executable forms and on any user documentation, prefaced with the following words: “All or portions of this licensed product (such portions are the “Software”) have been obtained under license from The General Hospital Corporation and are subject to the following terms and conditions:” (c) you preserve and maintain all applicable attributions, copyright notices and licenses included in or applicable to the Software; (d) modified versions of the Software must be clearly identified and marked as such, and must not be misrepresented as being the original Software’. So redistribution and derivative works ARE permitted, but only by propagating the entire agreement onto every copy — a share-alike-style condition, and the licence is not one of §10.7’s permissive names (CC0, CC-BY-4.0, ODC-By-1.0, PDDL). The agreement also states ‘The Software has been designed for research purposes only’ and ‘YOU ACKNOWLEDGE AND AGREE THAT CLINICAL APPLICATIONS ARE NEITHER RECOMMENDED NOR ADVISED.’ That fsaverage is FreeSurfer data is stated by FreeSurfer (FsAverage wiki: ‘The name of the fsaverage, and it can be found in the distribution itself: $FREESURFER_HOME/subjects/fsaverage’) and by MNE (10_background_freesurfer.py: ‘During installation, FreeSurfer copies a subject called fsaverage to $FREESURFER_HOME/subjects/fsaverage’), and by the copy itself: fsaverage/scripts/build-stamp.txt in MNE’s archive reads ‘freesurfer-x86_64-redhat-linux-gnu-dev4-20090216’. DISAGREEING STATEMENTS, all read 2026-09-18 and all of them silences rather than contradictions: MNE-Python’s copy carries no licence text — root.zip has 194 entries, read over HTTP range requests, and the only licence-ish file is fsaverage/mri.2mm/README, a technical note about 2 mm resampling that states no terms; OSF node rxvq7 returns node_license: None; the fsaverage section of MNE’s doc/documentation/datasets.rst names no licence and says only ‘For convenience, we provide a function to separately download and extract the (or update an existing) fsaverage subject’; and mne/datasets/config.py carries explicit licence text and a click-through gate for Brainstorm and HCP-MMP only, not for fsaverage. The two distribution channels also disagree about access (see access_steps). Per §10.7 the most restrictive reading governs, so snippets derives to ‘no’ three times over (non-permissive licence name; access: registration; license_status: contested). Shipping anything derived from fsaverage would need an explicit author license_decision of the §13 item 15 kind, and that decision would have to address propagating the FreeSurfer agreement onto every derived asset.
• Snippets on this site: no — the site ships no snippet or precomputed product from this dataset; lessons link the official access page.

Acquisition

Field	Value
Device	n/a — anatomical template, not a recording
Device class	TODO(confirm)
Channels	TODO(confirm)
Sampling rate (Hz)	TODO(confirm)
Online filters	TODO(confirm)
Reference	TODO(confirm)
Mains frequency (Hz)	TODO(confirm)
Paradigms	none
Participants	40 (40 MRI scans averaged into one template; the template is a single subject directory, not 40 releasable subjects, and the individual scans are not part of it)
Population	a template built by averaging 40 MRI scans of real brains (MNE-Python tutorials/forward/10_background_freesurfer.py: ‘fsaverage is a template brain based on a combination of 40 MRI scans of real brains’). The FreeSurfer wiki page that documents those subjects (Buckner40) returns ‘You are not allowed to view this page’ to an anonymous reader, so who they were and on what terms their scans were shared cannot be checked from the public record. TODO(confirm)
Clinical groups	none
Sessions	TODO(confirm)
Durations	Template anatomy for forward models (§10.2): surfaces, volumes, parcellations, and — in MNE’s copy — a head surface, fiducials, a head-to-MRI transform and 1- and 3-layer BEM surfaces and solutions

Used on this site

L5.4, L5.5, L5.6, C5

Loader

Fetches only the stated subset. Recorded loader: mne.datasets.fetch_fsaverage() — fetches MNE's copy only; the FreeSurfer distribution route needs the free licence key above.

# TODO(confirm): loader recorded from the MNE API, not from the catalog.
import mne
fs_dir = mne.datasets.fetch_fsaverage()
subjects_dir = fs_dir.parent

Caveats worth knowing

• No asset derived from fsaverage ships on this site. The FreeSurfer Software License Agreement permits derivative works but requires the whole agreement to be propagated onto every copy, which is not one of §10.7’s permissive licences; the lesson says so instead of showing a precomputed realistic-head-model map.
• The data as distributed carries no licence file. MNE’s fsaverage archive contains no LICENSE, the OSF node that serves it records no licence, and MNE’s documentation names none — the licence has to be traced back to the FreeSurfer distribution the template comes from.
• fsaverage is an average of 40 brains, so it is nobody’s anatomy. Localization error against an individual MRI is a property of the template, not of the method, and §6 L5.4 is where that is taught.
• The provenance of the 40 scans cannot be checked from the public record: FreeSurfer’s Buckner40 wiki page is not readable anonymously.
• Not in the author’s catalog: every fact here was read from FreeSurfer’s and MNE-Python’s own primary material on 2026-09-18, not from data/catalog (§10.1 rule 3). The author should add a registry stub (§10.11 item 8).

Related datasets

• ERP CORE (Compendium of Open Resources and Experiments)
• EEG Motor Movement/Imagery Dataset (EEGMMIDB)
• LEMON (MPI-Leipzig Mind-Brain-Body)
• Dortmund Vital Study resting EEG
• SRM Resting-state EEG

# Loader recorded in the catalog: mne.datasets.fetch_fsaverage() — fetches MNE's copy only; the FreeSurfer distribution route needs the free licence key above
# Fetch only the subset you need; see the loader's docstring for subject/run arguments.
import mne

files = mne.datasets.fetch_fsaverage() — fetches MNE's copy only; the FreeSurfer distribution route needs the free licence key above(...)  # TODO(confirm) subset arguments