Compute time-frequency maps of power and phase lock in the source space. The inverse method is linear based on dSPM inverse operator.

The example also shows the difference in the time-frequency maps when they are computed with and without subtracting the evoked response from each epoch. The former results in induced activity only while the latter also includes evoked (stimulus-locked) activity.

```
# Authors: Alexandre Gramfort <alexandre.gramfort@telecom-paristech.fr>
#
# License: BSD (3-clause)
import numpy as np
import matplotlib.pyplot as plt
import mne
from mne import io
from mne.datasets import sample
from mne.minimum_norm import read_inverse_operator, source_induced_power
print(__doc__)
```

Set parameters

```
data_path = sample.data_path()
raw_fname = data_path + '/MEG/sample/sample_audvis_raw.fif'
fname_inv = data_path + '/MEG/sample/sample_audvis-meg-oct-6-meg-inv.fif'
label_name = 'Aud-rh'
fname_label = data_path + '/MEG/sample/labels/%s.label' % label_name
tmin, tmax, event_id = -0.2, 0.5, 2
# Setup for reading the raw data
raw = io.read_raw_fif(raw_fname)
events = mne.find_events(raw, stim_channel='STI 014')
inverse_operator = read_inverse_operator(fname_inv)
include = []
raw.info['bads'] += ['MEG 2443', 'EEG 053'] # bads + 2 more
# Picks MEG channels
picks = mne.pick_types(raw.info, meg=True, eeg=False, eog=True,
stim=False, include=include, exclude='bads')
reject = dict(grad=4000e-13, mag=4e-12, eog=150e-6)
# Load epochs
epochs = mne.Epochs(raw, events, event_id, tmin, tmax, picks=picks,
baseline=(None, 0), reject=reject,
preload=True)
# Compute a source estimate per frequency band including and excluding the
# evoked response
frequencies = np.arange(7, 30, 2) # define frequencies of interest
label = mne.read_label(fname_label)
n_cycles = frequencies / 3. # different number of cycle per frequency
# subtract the evoked response in order to exclude evoked activity
epochs_induced = epochs.copy().subtract_evoked()
plt.close('all')
for ii, (this_epochs, title) in enumerate(zip([epochs, epochs_induced],
['evoked + induced',
'induced only'])):
# compute the source space power and the inter-trial coherence
power, itc = source_induced_power(
this_epochs, inverse_operator, frequencies, label, baseline=(-0.1, 0),
baseline_mode='percent', n_cycles=n_cycles, n_jobs=1)
power = np.mean(power, axis=0) # average over sources
itc = np.mean(itc, axis=0) # average over sources
times = epochs.times
##########################################################################
# View time-frequency plots
plt.subplots_adjust(0.1, 0.08, 0.96, 0.94, 0.2, 0.43)
plt.subplot(2, 2, 2 * ii + 1)
plt.imshow(20 * power,
extent=[times[0], times[-1], frequencies[0], frequencies[-1]],
aspect='auto', origin='lower', vmin=0., vmax=30., cmap='RdBu_r')
plt.xlabel('Time (s)')
plt.ylabel('Frequency (Hz)')
plt.title('Power (%s)' % title)
plt.colorbar()
plt.subplot(2, 2, 2 * ii + 2)
plt.imshow(itc,
extent=[times[0], times[-1], frequencies[0], frequencies[-1]],
aspect='auto', origin='lower', vmin=0, vmax=0.7,
cmap='RdBu_r')
plt.xlabel('Time (s)')
plt.ylabel('Frequency (Hz)')
plt.title('ITC (%s)' % title)
plt.colorbar()
plt.show()
```

Out:

```
Opening raw data file /home/ubuntu/mne_data/MNE-sample-data/MEG/sample/sample_audvis_raw.fif...
Read a total of 3 projection items:
PCA-v1 (1 x 102) idle
PCA-v2 (1 x 102) idle
PCA-v3 (1 x 102) idle
Range : 25800 ... 192599 = 42.956 ... 320.670 secs
Ready.
Current compensation grade : 0
320 events found
Events id: [ 1 2 3 4 5 32]
Reading inverse operator decomposition from /home/ubuntu/mne_data/MNE-sample-data/MEG/sample/sample_audvis-meg-oct-6-meg-inv.fif...
Reading inverse operator info...
[done]
Reading inverse operator decomposition...
[done]
305 x 305 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 60) active
Noise covariance matrix read.
22494 x 22494 diagonal covariance (kind = 2) found.
Source covariance matrix read.
22494 x 22494 diagonal covariance (kind = 6) found.
Orientation priors read.
22494 x 22494 diagonal covariance (kind = 5) found.
Depth priors read.
Did not find the desired covariance matrix (kind = 3)
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
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
Source spaces transformed to the inverse solution coordinate frame
73 matching events found
Created an SSP operator (subspace dimension = 3)
3 projection items activated
Loading data for 73 events and 421 original time points ...
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on MAG : [u'MEG 1711']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
Rejecting epoch based on EOG : [u'EOG 061']
14 bad epochs dropped
Subtracting Evoked from Epochs
The following channels are not included in the subtraction: EOG 061
[done]
Preparing the inverse operator for use...
Scaled noise and source covariance from nave = 1 to nave = 1
Created the regularized inverter
Created an SSP operator (subspace dimension = 3)
Created the whitener using a full noise covariance matrix (3 small eigenvalues omitted)
Computing noise-normalization factors (dSPM)...
[done]
Picked 305 channels from the data
Computing inverse...
(eigenleads need to be weighted)...
Reducing data rank to 81
Computing source power ...
Applying baseline correction (mode: percent)
Preparing the inverse operator for use...
Scaled noise and source covariance from nave = 1 to nave = 1
Created the regularized inverter
Created an SSP operator (subspace dimension = 3)
Created the whitener using a full noise covariance matrix (3 small eigenvalues omitted)
Computing noise-normalization factors (dSPM)...
[done]
Picked 305 channels from the data
Computing inverse...
(eigenleads need to be weighted)...
Reducing data rank to 81
Computing source power ...
Applying baseline correction (mode: percent)
```

**Total running time of the script:** ( 0 minutes 21.838 seconds)