.. DO NOT EDIT. .. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY. .. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE: .. "auto_examples/04_glm_first_level/plot_hrf.py" .. LINE NUMBERS ARE GIVEN BELOW. .. only:: html .. note:: :class: sphx-glr-download-link-note :ref:`Go to the end ` to download the full example code or to run this example in your browser via Binder .. rst-class:: sphx-glr-example-title .. _sphx_glr_auto_examples_04_glm_first_level_plot_hrf.py: Example of MRI response functions ================================= Within this example we are going to plot the hemodynamic response function (:term:`HRF`) model in :term:`SPM` together with the :term:`HRF` shape proposed by G.Glover, as well as their time and dispersion derivatives. We also illustrate how users can input a custom response function, which can for instance be useful when dealing with non human primate data acquired using a contrast agent. In our case, we input a custom response function for MION, a common `agent `_ used to enhance contrast on MRI images of monkeys. The :term:`HRF` is the filter which couples neural responses to the metabolic-related changes in the MRI signal. :term:`HRF` models are simply phenomenological. In current analysis frameworks, the choice of :term:`HRF` model is essentially left to the user. Fortunately, using the :term:`SPM` or Glover model does not make a huge difference. Adding derivatives should be considered whenever timing information has some degree of uncertainty, and is actually useful to detect timing issues. This example requires matplotlib and scipy. .. GENERATED FROM PYTHON SOURCE LINES 29-35 .. code-block:: Python try: import matplotlib.pyplot as plt except ImportError: raise RuntimeError("This script needs the matplotlib library") .. GENERATED FROM PYTHON SOURCE LINES 36-41 Define stimulus parameters and response models ---------------------------------------------- To get an impulse response, we simulate a single event occurring at time t=0, with duration 1s. .. GENERATED FROM PYTHON SOURCE LINES 41-49 .. code-block:: Python import numpy as np time_length = 30.0 frame_times = np.linspace(0, time_length, 61) onset, amplitude, duration = 0.0, 1.0, 1.0 exp_condition = np.array((onset, duration, amplitude)).reshape(3, 1) .. GENERATED FROM PYTHON SOURCE LINES 50-51 Make a time array of this condition for display: .. GENERATED FROM PYTHON SOURCE LINES 51-54 .. code-block:: Python stim = np.zeros_like(frame_times) stim[(frame_times > onset) * (frame_times <= onset + duration)] = amplitude .. GENERATED FROM PYTHON SOURCE LINES 55-57 Define custom response functions for MION. Custom response functions should at least take :term:`TR` and oversampling as arguments: .. GENERATED FROM PYTHON SOURCE LINES 57-118 .. code-block:: Python from scipy.stats import gamma def mion_response_function(tr, oversampling=16, onset=0.0): """Implement the MION response function model. Parameters ---------- tr: float scan repeat time, in seconds oversampling: int, optional temporal oversampling factor onset: float, optional hrf onset time, in seconds Returns ------- response_function: array of shape(length / tr * oversampling, dtype=float) response_function sampling on the oversampled time grid """ dt = tr / oversampling time_stamps = np.linspace( 0, time_length, np.rint(time_length / dt).astype(int) ) time_stamps -= onset # parameters of the gamma function delay = 1.55 dispersion = 5.5 response_function = gamma.pdf(time_stamps, delay, loc=0, scale=dispersion) response_function /= response_function.sum() response_function *= -1 return response_function def mion_time_derivative(tr, oversampling=16.0): """Implement the MION time derivative response function model. Parameters ---------- tr: float scan repeat time, in seconds oversampling: int, optional temporal oversampling factor, optional Returns ------- drf: array of shape(time_length / tr * oversampling, dtype=float) derived_response_function sampling on the provided grid """ do = 0.1 drf = ( mion_response_function(tr, oversampling) - mion_response_function(tr, oversampling, do) ) / do return drf .. GENERATED FROM PYTHON SOURCE LINES 119-120 Define response function models to be displayed: .. GENERATED FROM PYTHON SOURCE LINES 120-131 .. code-block:: Python rf_models = [ ("spm + derivative + dispersion", "SPM HRF", None), ("glover + derivative + dispersion", "Glover HRF", None), ( [mion_response_function, mion_time_derivative], "Mion RF + derivative", ["main", "main_derivative"], ), ] .. GENERATED FROM PYTHON SOURCE LINES 132-134 Sample and plot response functions ---------------------------------- .. GENERATED FROM PYTHON SOURCE LINES 134-169 .. code-block:: Python from nilearn.glm.first_level import compute_regressor oversampling = 16 fig = plt.figure(figsize=(9, 4)) for i, (rf_model, model_title, labels) in enumerate(rf_models): # compute signal of interest by convolution signal, _labels = compute_regressor( exp_condition, rf_model, frame_times, con_id="main", oversampling=oversampling, ) # plot signal plt.subplot(1, len(rf_models), i + 1) plt.fill(frame_times, stim, "k", alpha=0.5, label="stimulus") for j in range(signal.shape[1]): plt.plot( frame_times, signal.T[j], label=( labels[j] if labels is not None else (_labels[j] if _labels is not None else None) ), ) plt.xlabel("time (s)") plt.legend(loc=1) plt.title(model_title) # adjust plot plt.subplots_adjust(bottom=0.12) plt.show() .. image-sg:: /auto_examples/04_glm_first_level/images/sphx_glr_plot_hrf_001.png :alt: SPM HRF, Glover HRF, Mion RF + derivative :srcset: /auto_examples/04_glm_first_level/images/sphx_glr_plot_hrf_001.png :class: sphx-glr-single-img .. rst-class:: sphx-glr-timing **Total running time of the script:** (0 minutes 1.778 seconds) **Estimated memory usage:** 9 MB .. _sphx_glr_download_auto_examples_04_glm_first_level_plot_hrf.py: .. only:: html .. container:: sphx-glr-footer sphx-glr-footer-example .. container:: binder-badge .. image:: images/binder_badge_logo.svg :target: https://mybinder.org/v2/gh/nilearn/nilearn/0.10.4?urlpath=lab/tree/notebooks/auto_examples/04_glm_first_level/plot_hrf.ipynb :alt: Launch binder :width: 150 px .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: plot_hrf.ipynb ` .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: plot_hrf.py ` .. only:: html .. rst-class:: sphx-glr-signature `Gallery generated by Sphinx-Gallery `_