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%matplotlib inline

Time-frequency representations on topographies for MEG sensors

Both average power and intertrial coherence are displayed.



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# Authors: Alexandre Gramfort <alexandre.gramfort@telecom-paristech.fr>
#          Denis Engemann <denis.engemann@gmail.com>
#
# License: BSD (3-clause)

import numpy as np
import matplotlib.pyplot as plt

import mne
from mne import io
from mne.time_frequency import tfr_morlet
from mne.datasets import somato

print(__doc__)

Set parameters



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data_path = somato.data_path()
raw_fname = data_path + '/MEG/somato/sef_raw_sss.fif'
event_id, tmin, tmax = 1, -1., 3.

# Setup for reading the raw data
raw = io.Raw(raw_fname)
baseline = (None, 0)
events = mne.find_events(raw, stim_channel='STI 014')

# picks MEG gradiometers
picks = mne.pick_types(raw.info, meg='grad', eeg=False, eog=True, stim=False)

epochs = mne.Epochs(raw, events, event_id, tmin, tmax, picks=picks,
                    baseline=baseline, reject=dict(grad=4000e-13, eog=350e-6))

Calculate power and intertrial coherence



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freqs = np.arange(6, 30, 3)  # define frequencies of interest
n_cycles = freqs / 2.  # different number of cycle per frequency
power, itc = tfr_morlet(epochs, freqs=freqs, n_cycles=n_cycles, use_fft=True,
                        return_itc=True, decim=3, n_jobs=1)

# Baseline correction can be applied to power or done in plots
# To illustrate the baseline correction in plots the next line is commented
# power.apply_baseline(baseline=(-0.5, 0), mode='logratio')

# Inspect power
power.plot_topo(baseline=(-0.5, 0), mode='logratio', title='Average power')
power.plot([82], baseline=(-0.5, 0), mode='logratio')

fig, axis = plt.subplots(1, 2, figsize=(7, 4))
power.plot_topomap(ch_type='grad', tmin=0.5, tmax=1.5, fmin=8, fmax=12,
                   baseline=(-0.5, 0), mode='logratio', axes=axis[0],
                   title='Alpha', vmax=0.45)
power.plot_topomap(ch_type='grad', tmin=0.5, tmax=1.5, fmin=13, fmax=25,
                   baseline=(-0.5, 0), mode='logratio', axes=axis[1],
                   title='Beta', vmax=0.45)
mne.viz.tight_layout()

# Inspect ITC
itc.plot_topo(title='Inter-Trial coherence', vmin=0., vmax=1., cmap='Reds')