Introduction

Compile NML2 definitions to data compatible with Arbor https://github.com/arbor-sim/arbor. The nmlcc tool will consume a list of LEMS files containing NML2 conformant ComponentType definitions and a NeuroML2 file (.nml). From there, a series of exporters can be used to produce a templated Arbor simulation that can be customised to your needs.

When Should I Use This Instead of JNML?

1. If you are using Arbor anyway, this project produces output directly aimed at Arbor.
   • No editing of NMODL files.
   • No manual assigments of ion channels and parameters.
   • Basic support for stimuli.
   • Can emit a full simulation at once
2. The performance of nmlcc's NMODL channels is far superior, see below. Measured end-to-end simulation in Arbor (includes model construction) gives at least a 2x improvement. This is the result of automating lots of manual transformations we have learned while porting models to Arbor. In addition, mechanisms can be combined into 'super-mechansims' (SM) per assigned segment group and parameters inlined where possible, giving access to constant folding (CF).
3. If you are not using Arbor, you might still be able to profit from NMODL output. However this is not tested, use at your own risk. In general nmlcc produces simpler and cleaner NMODL files for what the models it understands than jnml.

When Shouldn't I Use This?

1. This project is quite early in its lifecycle, so expect bugs and missing features.
2. If you are not using Arbor. While NMODL export might work for NEURON, we do not test this nor do we plan support for it.
3. If you are not interested in multi-compartment models. Currently only MC-cells are supported.
4. Networks are supported, yet experimental. If you need automated export of networks. We are currently looking into this, but it is not yet supported.
5. If you are reliant on other features of jnml and/or jlems that are not supported in nmlcc.

Performance

Casual benchmarking on a 2018 i5 MacBook Pro gives these results

• HH tutorial cell from https://github.com/openworm/hodgkin_huxley_tutorial
  • simulation settings: t=1000 ms and dt=0.0025
  • soma-only morphology, d=17.8um discretized into 0.1um segments
  • three ion channels were assigned to the full cell: k, na, and passive
• Arbor 0.6 Release
  • Arbor was built from source using -march=native and the release profile.
  • using a single core of an 2018 Intel Core i5
  • times are measured across sim.run(...), thus model building is included

† Built using nmlcc bundle --super-mechanisms

Why is it so Fast?

nmlcc codifies a lot of the transformations on NMODL that we (the Arbor team) have learned over the last years of using, porting, and optimising NMODL. Here is an incomplete list

• Eliminate RANGE variables. Prefer (re-)computing everything locally instead, except the most expensive terms and those only if static.
• Similarly prefer CONSTANT over PARAMETER.
• Do not use PROCEDURE. These have to use ASSIGNED RANGE variables to return values. Inline the compuations instead or use FUNCTION.

It's a small set of quite obvious ideas once you have seen how NMODL is implemented by Arbor. Most of this is made possible by looking at the whole simulation encode in NML2 at once and building a bespoke models for Arbor from it. Also, NML2 requires a tiny subset of NMODL to implement. In the past, we applied this by hand to the jnml output, which is quite conservative. Crucially, nmlcc automates this process.

We take this idea one step further in the bundle exporter, if given the --super-mechanisms flag. There we group all density mechanisms assigned to a common subset of the morphology and generate a single NMODL file per such subset. Then, all parameter assigments are hard-coded into the NMODL output. This opens up more opportunities for optimisation and eliminates calls from Arbor into the mechanisms.

Getting Started

Install a recent version of the Rust language, using rustup or your favourite package manager. Then, clone this repo and try an example

git clone git@github.com:thorstenhater/nmlcc.git --recursive
cd nmlcc
cargo run -- nmodl example/nml-simple-ion-channels.xml

This will build the nmlcc compiler and all its dependencies, which can take a bit. The final output should be a file NaConductance.mod in the current directory.

For an introduction on how to run an example in Arbor, see the tutorial in the docs directory. If you want an quick and easy way to convert NML2 cells to an Arbor single cell model, take a look at the bundle exporter here.

Usage

Note we use nmlcc as if calling the tool directly, when using cargo, replace nmlcc with cargo run -- [args] instead.

General Options

• -v/--verbose: Provide more output, defaults to warnings only, -v escalates to INFO and -vv to TRACE.

• --ions: Comma separated list of ion species to consider as given in the simulator, but does not allow for adding new species (for that use the <species> tag). The default is Arbor's list of ions Calcium Ca 2+, Sodium Na 1+, and Potassium K 1+. NeuroML2 defaults to just Ca and Na, so if you are trying to port an NML2 model 1:1 pass --ions='na,ca'. All ion names will be turned into lowercase.

  Any ionic species that is neither known, ie given via this flag or its defaults, or declared using an NML2 <species> will be turned into a non-specific current when exporting to NMODL.

Generate NMODL from NeuroML2 Dynamics

nmlcc nmodl <options> <input.nml ...> generates NMODL files that can be compiled into Arbor catalogues. Files will be written to <id>.mod in the current directory where <id> is the NML2 component id.

All ComponentTypes extending one of the following base classes will be turned into an NMODL file

• gapJunction produces gap junction models.
• baseSynapse (excluding gapJunction) will be exported as synapse models.
• ionChannelHH, ionChannel, and ionChannelKS become conductance based mechanisms producing an ionic current.
• concentrationModel becomes a density mechanism writing internal and external ion concentrations.

File names will be chosen as <id>.mod where the id is the NML2 id designator.

ConcentrationModel Support

In contrast to NML2 native models nmlcc replaces the Ca ion with the one speficied by the species attribute. If you intend to run concentration models in Arbor, you will need to adjust your NML2 description slightly. However, Arbor does not export surfaceArea as area -- as NEURON does -- since it dependes on the concrete discretised models. Instead, Arbor's NMODL dialect exposes the CV's diameter as the diam variable. Usually, this is not an issue, but concentration models may need the molar flux f across the membrane and reach for the formula f = -i A /(F q) where F is Faraday's constant, q the ionic charge, A the CV's surface area, and i the current density. This is difficult to model without being able to access the surface area. It might be acceptable to approximate the surface area as a sphere with A = π diam^2.

Options

• --dir=<dir>: store ouput under this directory, defaults to current directory.
• --parameter=+p,-q,..: will choose parameters to retain as tweakable, defaults to +* keeping all
  • -q excludes parameter q from the final list, unless overridden
  • +p similarly, will add p
  • a selector can end on wildcard * to select all suffixes
    • a wildcard anywhere else will be considered a literal * character
    • wildcards must be ordered from least to most specific, ie foo_bar_* must come after foo_* to have effect
  • consequently, -q_*,+q_a_*,-q_a_b will remove all parameters starting with q_, except if they start with q_a, but remove q_a_b.
  • when compiling channels derived from the following base types, we will alter the parameter list slightly in order to play nicely with export to ACC
    • baseIonChannel: +conductance, if non-specific currents are used +conductance,+e
    • baseVoltageDepSynapse: +gbase,+erev
    • gapJunction: +weight,+conductance
    • concentrationModel: no adjustments made

Example: Export a Simple Exponential Synapse

$> nmlcc nmodl --parameter='-*' example/nml-gap-junction.xml
$> cat gj1.mod
NEURON {
  JUNCTION gj1
  NONSPECIFIC_CURRENT i
  RANGE weight, conductance
}

PARAMETER {
  weight = 1
  conductance = 0.00000001 (mS)
}

BREAKPOINT {
  i = conductance * weight * (v_peer + -1 * v)
}

Despite being obviously auto-generated code, the produced NMODL files are quite clean and easy to tune further, if you need to eeke out the last bit of performance from your model.

Exporting Cells to Arbor Cable Cell Format (ACC)

nmlcc acc <options> <input.nml ...> extracts a Arbor Cable Cell description based on the biophysicalProperties found in the input file(s). Output will be stored as <id>.acc with id being the NML2 id of the associated cells. If you pass in a file containing whole <network> object, nmlcc will try to wire up stimuli as well.

Options

• --dir=<dir>: store ouput under this directory, defaults to current directory.

Example: Fetch Parameter Assignments from a Simple Cell Model

$> nmlcc acc --cell=hhcell example/nml-hh-cell.nml
$> cat hhcell.acc
(arbor-component
  (meta-data (version "0.1-dev"))
  (decor
    (paint (region "all") (density (mechanism "passiveChan" ("e" -54.387001037597656) ("conductance" 0.30000001192092896))))
    (default (ion-reversal-potential "na" 50))
    (paint (region "all") (density (mechanism "naChan" ("conductance" 120))))
    (default (ion-reversal-potential "k" -77))
    (paint (region "all") (density (mechanism "kChan" ("conductance" 36))))
    (default (membrane-capacitance 1))
    (default (membrane-potential -65.4000015258789))
    (default (axial-resistivity 0.029999999329447746))))

Producing a Ready-to-Run Bundle from NML2

Note: bundle accepts a single NML2 file instead of a list like the remainder of commands and expects to find at least a cell instance and preferably a network. If no network is found, some settings will not be available, eg adding ion species, concentration models, and temperature.

nmlcc bundle <input.nml> <output> combines the last two commands into a convenient package and adds another layer on top. The NML2 file <input.nml> must contain all morphologies needed for the relevant cells, prerably it should a complete <network> definition. The bundle exporter generates a directory <output> and fills it like follows (id refers to the NML id attribute found on the cell component):

• acc/*.acc: ACC files, one per cell found in <input.nml>, named <id>.acc.
• cat/*.nmodl: NMODL files, one per ComponentType derived from either baseIonChannel or baseSynapse, with parameter filters set to -*.
• mrf/*.nml: NML2 files containing extracted morphologies, one per cell, stored as <id>.nml
• main.<id>.py: template python script, one per id, to
  1. Build and install the catalogue from the NMODL file.
  2. Load the morphologies, parameter assignments, and labels.
  3. Connect stimuli, currently PulseGenerator only.
  4. Construct and execute a simulation.

After running the exporter, you will want to tweak a few settings

• Probes to measure observables, by default the membrane potential at the soma is probed.
• Extraction of measurement traces, by default we try to import seaborn and matplotlib and plot the soma probe.
• Simulation settings; defaults are time t=1000ms and dt=0.005ms.

Options

• --super-mechanisms: try to produce combined ion-channels per segment group while inlining all parameters. Can give a ~20-30% speed boost depending on your problem.

Current Limitations

• units are not treated completly, rather upon seeing a quantity, it will be converted to a 'blessed' unit for that dimension, eg 1 m will become 100 cm internally. This can have some consequences for accuracy.
• ACC export is only valid for Arbor 0.6.
• No support for
  • networks
  • simulations
  • cells other than the multi-compartment <cell> kind
• See also our issue tracker.

Bootstrapping the Compiler

This project comes with a pre-built data model in src/lems/raw.rs and src/neuroml/raw.rs. If you change the underlying LEMS/NML2 definitions or edit src/schema.rs you'll need to rebuild the data model by running this command

cargo run --bin schema

This will allow for tweaking the versions of the NML2/LEMS schemata or adjusting them by hand. The default state is produced by running this script

bash bootstrap.sh

which will

• bring in the LEMS and NML2 schemata
• (and remove them if present)
• slightly modify both of them
• build the data model from the schemata

By default the following definitions are used

• NML2: development branch; XSD v2.2
• LEMS: development branch; XSD v0.7.6

After adjusting the schemata or data model, you will need to re-compile the nmlcc binary (cargo build). Note that the core definitions found in ext/NeuroML2/NeuroML2CoreTypes are embedded into the nmlcc binary. This allows for moving it around without keeping track of NML2 definition.