mne_forward_solution

Overview

mne_forward_solution computes the MEG/EEG forward solution for source localization. It calculates the magnetic fields and electric potentials at the measurement sensors and electrodes due to dipole sources located on the cortex or in a volume source space.

This is a C++ port of the original MNE-C tool by Matti Hämäläinen.

Usage

mne_forward_solution [options]

Options

The command-line options are defined by the ComputeFwdSettings class and follow the standard MNE-C forward solution options. Key options include:

Option	Description
--src <file>	Source space file
--bem <file>	BEM model file
--meas <file>	Measurement data file (for sensor info)
--fwd <file>	Output forward solution file
--trans <file>	Head-MRI coordinate transform file
--meg	Compute MEG forward solution
--eeg	Compute EEG forward solution
--mindist <dist>	Minimum source-to-inner-skull distance (mm)
--accurate	Use accurate coil geometry descriptions
--fixed	Fixed source orientations (normal to cortex)
--all	Compute for all source space points

Description

The forward solution is a critical component of the MEG/EEG source localization pipeline. It maps the relationship between source currents on the cortex (or in the volume) and the measured signals at the MEG sensors and EEG electrodes.

Prerequisites

Before computing the forward solution, the following must be available:

1. Source space — Created from FreeSurfer surface reconstruction
2. BEM model — Created using mne_watershed_bem or mne_flash_bem, then set up with mne_setup_forward_model
3. Coordinate transformation — The head-to-MRI transform stored in a -trans.fif file
4. Measurement info — A FIFF file containing sensor locations and orientations

BEM vs. Sphere Model

The forward solution can be computed using either:

• BEM (Boundary Element Model) — More accurate, requires BEM surfaces
• Sphere model — Simpler, uses concentric sphere approximation

Software Gradient Compensation

For CTF and 4D Neuroimaging data that has been subjected to software gradient compensation, the forward solution automatically accounts for the reference sensor array and computes a compensated forward solution.

Example

Compute a MEG forward solution:

mne_forward_solution \
    --src sample-oct6-src.fif \
    --bem sample-5120-5120-5120-bem-sol.fif \
    --meas sample_audvis_raw.fif \
    --trans sample-trans.fif \
    --meg \
    --fwd sample-meg-fwd.fif

Compute a combined MEG+EEG forward solution with accurate coil descriptions:

mne_forward_solution \
    --src sample-oct6-src.fif \
    --bem sample-5120-5120-5120-bem-sol.fif \
    --meas sample_audvis_raw.fif \
    --trans sample-trans.fif \
    --meg --eeg --accurate \
    --fwd sample-meg-eeg-fwd.fif