2.4.2. Example of hemodynamic reponse functions.

Plot the hemodynamic reponse function (hrf) model in SPM together with the hrf shape proposed by G.Glover, as well as their time and dispersion derivatives.

Requires matplotlib.

The hrf is the filter that couples neural responses to the metabolic-related changes in the MRI signal. hrf models are simply phenomenological.

In current analysis frameworks, the choice of hrf model is essentially left to the user. Fortunately, using spm or Glover model does not make a huge difference. Adding derivatives should be considered whenever timing information has some degree of uncertainty. It is actually useful to detect timing issues.

2.4.2.1. Set up some parameters for model display

To get an impulse reponse, we simulate a single event occurring at time t=0, with duration 1s.

import numpy as np
frame_times = np.linspace(0, 30, 61)
onset, amplitude, duration = 0., 1., 1.
exp_condition = np.array((onset, duration, amplitude)).reshape(3, 1)

Sample this on a fris for display

stim = np.zeros_like(frame_times)
stim[(frame_times > onset) * (frame_times <= onset + duration)] = amplitude

Define the candidate hrf models

hrf_models = [None, 'glover + derivative', 'glover + derivative + dispersion']

2.4.2.2. sample the hrf

from nistats import hemodynamic_models
import matplotlib.pyplot as plt

fig = plt.figure(figsize=(9, 4))
for i, hrf_model in enumerate(hrf_models):
    # obtain the signal of interest by convolution
    signal, name = hemodynamic_models.compute_regressor(
        exp_condition, hrf_model, frame_times, con_id='main',
        oversampling=16)

    # plot this
    plt.subplot(1, 3, i + 1)
    plt.fill(frame_times, stim, 'k', alpha=.5, label='stimulus')
    for j in range(signal.shape[1]):
        plt.plot(frame_times, signal.T[j], label=name[j])
    plt.xlabel('time (s)')
    plt.legend(loc=1)
    plt.title(hrf_model)

# adjust the plot
plt.subplots_adjust(bottom=.12)
plt.show()
../../_images/sphx_glr_plot_hrf_001.png

Out:

/home/kshitij/.programs/anaconda3/envs/nistats-py36-latest/lib/python3.6/site-packages/matplotlib/figure.py:445: UserWarning: Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure.
  % get_backend())

Total running time of the script: ( 0 minutes 0.228 seconds)

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