PyFibers

PyFibers Paper: Marshall DP, Farah ES, Musselman ED, Pelot NA, Grill WM (2025) PyFibers: An open-source NEURON-Python package to simulate responses of model nerve fibers to electrical stimulation. PLoS Comput Biol 21(12): e1013764. https://doi.org/10.1371/journal.pcbi.1013764

This package implements biophysical models of axons in the NEURON simulation environment using Python. With our package, you can model the responses of axons to electrical stimulation (e.g., find the minimum current amplitude required to activate or block an action potential). You can add your own fiber models and simulations protocols. You can use analytical tools for extracellular potentials, or use outputs from finite element models (FEM) such as COMSOL, ANSYS, or FEniCS.

Installation

Note that these installation instructions are for users. Developer instructions are available in contributing.md.

It is recommended (But not required) you create a new virtual environment for PyFibers. For example, using Anaconda/Miniconda:

• conda create -n pyfibers
• conda activate pyfibers

1. Install NEURON and add to PATH (https://nrn.readthedocs.io/en/latest/)
   • Make sure your NEURON and Python versions are compatible (https://nrn.readthedocs.io/en/latest/changelog.html)
   • Check your installation by running the following command: python -c "import neuron; neuron.test(); quit()". If successful, test outputs along with "OK" should be printed to the terminal.
2. Install PyFibers from PyPI and compile the .mod files.

   pip install pyfibers
   pyfibers_compile
   

Some notes for pyfibers_compile:

• Check the NEURON output that follows for a message that the mechanisms were compiled successfully (e.g., for Windows: nrnmech.dll was built successfully.) While using PyFibers, if you see the NEURON mechanisms not found in <path>. message, this is cause for concern, as this means PyFibers cannot find the compiled mechanisms. Failed compiles will commonly cause the error message Argument not a density mechanism name to appear when trying to create fibers.
• Careful! Make sure that the correct NEURON installation is in your path, as the first found installation will be used for compilation. The version used for compilation must be the same version used to run PyFibers code.
• If you receive a message that the pyfibers_compile command is not found, find the executable for this command in the Scripts path of your python directory (e.g. C:\Users\<username>\Anaconda3\envs\pyfibers\Scripts) and run the executable (e.g., pyfibers_compile.exe).

Usage

📖 Documentation: For detailed information on usage, see our documentation:

• Tutorials on various operations.
• API Documentation on function/class arguments and outputs.

The basic steps for running a PyFibers simulation are as follows:

Creating a model fiber

Use the build_fiber function to create a fiber object. The fiber object consists of NEURON sections with ion channel mechanisms inserted for the fiber model chosen when the object is initialized. Users can add custom fiber models as well as use our provided models (see Custom Fiber Models).

from pyfibers import build_fiber

fiber = build_fiber(
    fiber_model=FiberModel.MRG_DISCRETE,
    diameter=10,  # um
    n_nodes=25,  # um
    temperature=37,  # C
)

Adding extracellular potentials

PyFibers supports both analytical calculations and using electrical potentials exported from solvers such as COMSOL or Ansys (see Extracellular Potentials documentation):

# Add extracellular potentials using point source approximation
fiber.potentials = fiber.point_source_potentials(0, 100, fiber.length / 2, 1, 0.3)

Running a simulation

To run a simulation with extracellular stimulation, use the ScaledStim class; users can also create custom simulation setups (See Custom Simulations) or use IntraStim for intracellular stimulation.

# Create instance of ScaledStim class
stimulation = ScaledStim(waveform=waveform, dt=time_step, tstop=time_stop)

# Run threshold search
amp, _ = stimulation.find_threshold(fiber)
print(f"Threshold for 5.7 micron fiber: {amp} (mA)")

For more examples, see the documentation.

Logging

PyFibers provides helpful logging messages during simulations. By default, logging is disabled to avoid interfering with your application's logging configuration.

To enable logging:

import pyfibers

pyfibers.enable_logging()  # Enable INFO level logging

For detailed logging configuration options, see the API documentation.

Contributing

If you develop additional functionality that would be generally useful to our users, please open a Pull Request for us to review. For detailed contribution guidelines, see our contributing guide.

Authors and acknowledgment

• Developed at Duke University by Daniel Marshall, Elie Farah, and Eric Musselman
• Associated publication: https://doi.org/10.1371/journal.pcbi.1013764

License

See LICENSE