Compute MxNE with time-frequency sparse priorΒΆ

The TF-MxNE solver is a distributed inverse method (like dSPM or sLORETA) that promotes focal (sparse) sources (such as dipole fitting techniques). The benefit of this approach is that:

  • it is spatio-temporal without assuming stationarity (sources properties can vary over time)
  • activations are localized in space, time and frequency in one step.
  • with a built-in filtering process based on a short time Fourier transform (STFT), data does not need to be low passed (just high pass to make the signals zero mean).
  • the solver solves a convex optimization problem, hence cannot be trapped in local minima.

References:

A. Gramfort, D. Strohmeier, J. Haueisen, M. Hamalainen, M. Kowalski Time-Frequency Mixed-Norm Estimates: Sparse M/EEG imaging with non-stationary source activations Neuroimage, Volume 70, 15 April 2013, Pages 410-422, ISSN 1053-8119, DOI: 10.1016/j.neuroimage.2012.12.051.

A. Gramfort, D. Strohmeier, J. Haueisen, M. Hamalainen, M. Kowalski Functional Brain Imaging with M/EEG Using Structured Sparsity in Time-Frequency Dictionaries Proceedings Information Processing in Medical Imaging Lecture Notes in Computer Science, 2011, Volume 6801/2011, 600-611, DOI: 10.1007/978-3-642-22092-0_49 http://dx.doi.org/10.1007/978-3-642-22092-0_49

# Author: Alexandre Gramfort <alexandre.gramfort@telecom-paristech.fr>
#
# License: BSD (3-clause)

import mne
from mne.datasets import sample
from mne.minimum_norm import make_inverse_operator, apply_inverse
from mne.inverse_sparse import tf_mixed_norm
from mne.viz import plot_sparse_source_estimates

print(__doc__)

data_path = sample.data_path()
subjects_dir = data_path + '/subjects'
fwd_fname = data_path + '/MEG/sample/sample_audvis-meg-eeg-oct-6-fwd.fif'
ave_fname = data_path + '/MEG/sample/sample_audvis-no-filter-ave.fif'
cov_fname = data_path + '/MEG/sample/sample_audvis-shrunk-cov.fif'

# Read noise covariance matrix
cov = mne.read_cov(cov_fname)

# Handling average file
condition = 'Left visual'
evoked = mne.read_evokeds(ave_fname, condition=condition, baseline=(None, 0))
evoked = mne.pick_channels_evoked(evoked)
# We make the window slightly larger than what you'll eventually be interested
# in ([-0.05, 0.3]) to avoid edge effects.
evoked.crop(tmin=-0.1, tmax=0.4)

# Handling forward solution
forward = mne.read_forward_solution(fwd_fname, force_fixed=False,
                                    surf_ori=True)

Out:

365 x 365 full covariance (kind = 1) found.
    Read a total of 4 projection items:
        PCA-v1 (1 x 102) active
        PCA-v2 (1 x 102) active
        PCA-v3 (1 x 102) active
        Average EEG reference (1 x 59) active
Reading /home/ubuntu/mne_data/MNE-sample-data/MEG/sample/sample_audvis-no-filter-ave.fif ...
    Read a total of 4 projection items:
        PCA-v1 (1 x 102) active
        PCA-v2 (1 x 102) active
        PCA-v3 (1 x 102) active
        Average EEG reference (1 x 60) active
    Found the data of interest:
        t =    -199.80 ...     499.49 ms (Left visual)
        0 CTF compensation matrices available
        nave = 64 - aspect type = 100
Projections have already been applied. Setting proj attribute to True.
Applying baseline correction (mode: mean)
Reading forward solution from /home/ubuntu/mne_data/MNE-sample-data/MEG/sample/sample_audvis-meg-eeg-oct-6-fwd.fif...
    Reading a source space...
    Computing patch statistics...
    Patch information added...
    Distance information added...
    [done]
    Reading a source space...
    Computing patch statistics...
    Patch information added...
    Distance information added...
    [done]
    2 source spaces read
    Desired named matrix (kind = 3523) not available
    Read MEG forward solution (7498 sources, 306 channels, free orientations)
    Desired named matrix (kind = 3523) not available
    Read EEG forward solution (7498 sources, 60 channels, free orientations)
    MEG and EEG forward solutions combined
    Source spaces transformed to the forward solution coordinate frame
    Converting to surface-based source orientations...
    Average patch normals will be employed in the rotation to the local surface coordinates....
[done]

Run solver

# alpha_space regularization parameter is between 0 and 100 (100 is high)
alpha_space = 50.  # spatial regularization parameter
# alpha_time parameter promotes temporal smoothness
# (0 means no temporal regularization)
alpha_time = 1.  # temporal regularization parameter

loose, depth = 0.2, 0.9  # loose orientation & depth weighting

# Compute dSPM solution to be used as weights in MxNE
inverse_operator = make_inverse_operator(evoked.info, forward, cov,
                                         loose=loose, depth=depth)
stc_dspm = apply_inverse(evoked, inverse_operator, lambda2=1. / 9.,
                         method='dSPM')

# Compute TF-MxNE inverse solution
stc, residual = tf_mixed_norm(evoked, forward, cov, alpha_space, alpha_time,
                              loose=loose, depth=depth, maxit=200, tol=1e-4,
                              weights=stc_dspm, weights_min=8., debias=True,
                              wsize=16, tstep=4, window=0.05,
                              return_residual=True)

# Crop to remove edges
stc.crop(tmin=-0.05, tmax=0.3)
evoked.crop(tmin=-0.05, tmax=0.3)
residual.crop(tmin=-0.05, tmax=0.3)

# Show the evoked response and the residual for gradiometers
ylim = dict(grad=[-120, 120])
evoked.pick_types(meg='grad', exclude='bads')
evoked.plot(titles=dict(grad='Evoked Response: Gradiometers'), ylim=ylim,
            proj=True)

residual.pick_types(meg='grad', exclude='bads')
residual.plot(titles=dict(grad='Residuals: Gradiometers'), ylim=ylim,
              proj=True)
  • ../../_images/sphx_glr_plot_time_frequency_mixed_norm_inverse_001.png
  • ../../_images/sphx_glr_plot_time_frequency_mixed_norm_inverse_002.png

Out:

info["bads"] and noise_cov["bads"] do not match, excluding bad channels from both
Computing inverse operator with 364 channels.
    Created an SSP operator (subspace dimension = 4)
estimated rank (mag + grad): 302
Setting small MEG eigenvalues to zero.
Not doing PCA for MEG.
estimated rank (eeg): 58
Setting small EEG eigenvalues to zero.
Not doing PCA for EEG.
Total rank is 360
Creating the depth weighting matrix...
    203 planar channels
    limit = 7262/7498 = 10.020865
    scale = 2.58122e-08 exp = 0.9
Computing inverse operator with 364 channels.
Creating the source covariance matrix
Applying loose dipole orientations. Loose value of 0.2.
Whitening the forward solution.
Adjusting source covariance matrix.
Computing SVD of whitened and weighted lead field matrix.
    largest singular value = 5.96729
    scaling factor to adjust the trace = 9.38524e+18
Preparing the inverse operator for use...
    Scaled noise and source covariance from nave = 1 to nave = 64
    Created the regularized inverter
    Created an SSP operator (subspace dimension = 4)
    Created the whitener using a full noise covariance matrix (4 small eigenvalues omitted)
    Computing noise-normalization factors (dSPM)...
[done]
Picked 364 channels from the data
Computing inverse...
(eigenleads need to be weighted)...
combining the current components...
(dSPM)...
[done]
info["bads"] and noise_cov["bads"] do not match, excluding bad channels from both
Computing inverse operator with 364 channels.
    Created an SSP operator (subspace dimension = 4)
estimated rank (mag + grad): 302
Setting small MEG eigenvalues to zero.
Not doing PCA for MEG.
estimated rank (eeg): 58
Setting small EEG eigenvalues to zero.
Not doing PCA for EEG.
Reducing data rank to 360
Total rank is 360
Whitening lead field matrix.
Applying loose dipole orientations. Loose value of 0.2.
Reducing source space to 985 sources
Whitening data matrix.
Using block coordinate descent and active set approach
Iteration 1
Iteration 1
Iteration 2
Iteration 3
Iteration 1
Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5
Iteration 6
Iteration 7
Iteration 8
Iteration 9
Iteration 10
Iteration 11
Iteration 12
Iteration 13
Iteration 14
Convergence reached !
Iteration 1
Convergence reached !
Debiasing converged after 376 iterations max(|D - D0| = 1.305445e-07 < 1.000000e-06)
4 projection items deactivated
Created an SSP operator (subspace dimension = 4)
4 projection items activated
SSP projectors applied...
0 projection items deactivated
combining the current components...
[done]

View in 2D and 3D (“glass” brain like 3D plot)

plot_sparse_source_estimates(forward['src'], stc, bgcolor=(1, 1, 1),
                             opacity=0.1, fig_name="TF-MxNE (cond %s)"
                             % condition, modes=['sphere'], scale_factors=[1.])

time_label = 'TF-MxNE time=%0.2f ms'
clim = dict(kind='value', lims=[10e-9, 15e-9, 20e-9])
brain = stc.plot('sample', 'inflated', 'rh', views='medial',
                 clim=clim, time_label=time_label, smoothing_steps=5,
                 subjects_dir=subjects_dir, initial_time=150, time_unit='ms')
brain.add_label("V1", color="yellow", scalar_thresh=.5, borders=True)
brain.add_label("V2", color="red", scalar_thresh=.5, borders=True)
  • ../../_images/sphx_glr_plot_time_frequency_mixed_norm_inverse_003.png
  • ../../_images/sphx_glr_plot_time_frequency_mixed_norm_inverse_004.png
  • ../../_images/sphx_glr_plot_time_frequency_mixed_norm_inverse_005.png

Out:

Total number of active sources: 2
Updating smoothing matrix, be patient..
Smoothing matrix creation, step 1
Smoothing matrix creation, step 2
Smoothing matrix creation, step 3
Smoothing matrix creation, step 4
Smoothing matrix creation, step 5
colormap: fmin=1.00e-08 fmid=1.50e-08 fmax=2.00e-08 transparent=1

Total running time of the script: ( 0 minutes 30.333 seconds)

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