Note
Click here to download the full example code
Plotting topographic maps of evoked data¶
Load evoked data and plot topomaps for selected time points using multiple additional options.
# Authors: Christian Brodbeck <christianbrodbeck@nyu.edu>
# Tal Linzen <linzen@nyu.edu>
# Denis A. Engeman <denis.engemann@gmail.com>
# Mikołaj Magnuski <mmagnuski@swps.edu.pl>
#
# License: BSD (3-clause)
# sphinx_gallery_thumbnail_number = 5
import numpy as np
import matplotlib.pyplot as plt
from mne.datasets import sample
from mne import read_evokeds
print(__doc__)
path = sample.data_path()
fname = path + '/MEG/sample/sample_audvis-ave.fif'
# load evoked corresponding to a specific condition
# from the fif file and subtract baseline
condition = 'Left Auditory'
evoked = read_evokeds(fname, condition=condition, baseline=(None, 0))
Out:
Reading /home/circleci/mne_data/MNE-sample-data/MEG/sample/sample_audvis-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 Auditory)
0 CTF compensation matrices available
nave = 55 - aspect type = 100
Projections have already been applied. Setting proj attribute to True.
Applying baseline correction (mode: mean)
Basic plot_topomap options¶
We plot evoked topographies using mne.Evoked.plot_topomap()
. The first
argument, times
allows to specify time instants (in seconds!) for which
topographies will be shown. We select timepoints from 50 to 150 ms with a
step of 20ms and plot magnetometer data:
times = np.arange(0.05, 0.151, 0.02)
evoked.plot_topomap(times, ch_type='mag', time_unit='s')

If times is set to None at most 10 regularly spaced topographies will be shown:
evoked.plot_topomap(ch_type='mag', time_unit='s')

Instead of showing topographies at specific time points we can compute averages of 50 ms bins centered on these time points to reduce the noise in the topographies:
evoked.plot_topomap(times, ch_type='mag', average=0.05, time_unit='s')

We can plot gradiometer data (plots the RMS for each pair of gradiometers)
evoked.plot_topomap(times, ch_type='grad', time_unit='s')

Additional plot_topomap options¶
We can also use a range of various mne.viz.plot_topomap()
arguments
that control how the topography is drawn. For example:
cmap
- to specify the color mapres
- to control the resolution of the topographies (lower resolution means faster plotting)outlines='skirt'
to see the topography stretched beyond the head circlecontours
to define how many contour lines should be plotted
evoked.plot_topomap(times, ch_type='mag', cmap='Spectral_r', res=32,
outlines='skirt', contours=4, time_unit='s')

If you look at the edges of the head circle of a single topomap you’ll see
the effect of extrapolation. By default extrapolate='box'
is used which
extrapolates to a large box stretching beyond the head circle.
Compare this with extrapolate='head'
(second topography below) where
extrapolation goes to 0 at the head circle and extrapolate='local'
where
extrapolation is performed only within some distance from channels:
extrapolations = ['box', 'head', 'local']
fig, axes = plt.subplots(figsize=(7.5, 2.5), ncols=3)
for ax, extr in zip(axes, extrapolations):
evoked.plot_topomap(0.1, ch_type='mag', size=2, extrapolate=extr, axes=ax,
show=False, colorbar=False)
ax.set_title(extr, fontsize=14)

More advanced usage¶
Now we plot magnetometer data as topomap at a single time point: 100 ms post-stimulus, add channel labels, title and adjust plot margins:
evoked.plot_topomap(0.1, ch_type='mag', show_names=True, colorbar=False,
size=6, res=128, title='Auditory response',
time_unit='s')
plt.subplots_adjust(left=0.01, right=0.99, bottom=0.01, top=0.88)

Animating the topomap¶
Instead of using a still image we can plot magnetometer data as an animation (animates only in matplotlib interactive mode)
evoked.animate_topomap(ch_type='mag', times=times, frame_rate=10,
time_unit='s')

Out:
Initializing animation...
Total running time of the script: ( 0 minutes 4.106 seconds)
Estimated memory usage: 8 MB