Key terms and goals:
Mechanistic or phenomenological multiscale modeling and simulation (M&S) in biomedical research continues to expand. Computational neuroscience (CNS) for modeling of brain disease faces unique challenges. CNS is starting to catch up with modeling of other organ systems but is also held back by its legacy in electrical engineering -- i.e. modeling electrophysiology but ignoring chemophysiology.
There is danger in using untested models to determine therapy for clinical practice. However, not having or not using models also presents dangers: treatments are currently used without understanding of what they are doing. Evidence-based medicine (EBM) can not help us develop personalized and precision medicine approaches. It is desirable to begin to develop credible model-based medicine.
To enhance credibility, the CPMS has developed 10 simple rules (TSR).
Replicability I can run your simulation and get exactly the same thing
Reproducibility I can recreate your simulation and get similar results.
Standards are standard in engineering
V&V: Verification and Validation
Validation: "definition and use of metrics for comparing experiment to simulation … design and execution of validation experiments"
(The Question: did we use the right model of biology?)
Code verification: "comparison of benchmark or analytic solutions to selected code outputs"
Solution Verification - "numerical error estimation … analysis of convergence"
(The Question: did we get an adequate numerical solution?)
Uncertainty Quantification: "quantification of uncertainties in experimental data and computational outputs"
(definitions from www.asme.org/events/vandv 17jun23)
V&V 40: Verification and Validation in Computational Modeling of Medical Devices
Rule 1 | Define context clearly: Develop and document the subject, purpose, and intended use(s) of the model or simulation. |
Rule 2 | Use appropriate data: Employ relevant and traceable information in the development or operation of a model or simulation. |
Rule 3 | Evaluate within context: Verification, validation, uncertainty quantification, and sensitivity analysis of the model or simulation with respect to experimental reality and to intended use. |
Rule 4 | List limitations explicitly: Identify restrictions, constraints, qualifications on the use of the model. |
Rule 5 | Use version control: Be able to trace the time history of modeling progress including parameter provenance and contributors' efforts. |
Rule 6 | Document thoroughly: Maintain laboratory notebooks with up-to-date informative records code development, model mark-up, model use and testing, etc. Develop user and developer guides and tutorials. |
Rule 7 | Disseminate broadly: Publish and make downloadable all components of activities, including simulation software, models, simulation scenarios and results. |
Rule 8 | Get independent reviews: Have the model reviewed by nonpartisan third-party users and developers. |
Rule 9 | Test competing implementations: Use different execution strategies, implementations, software packages to check the results. |
Rule 10 | Conform to standards: Adopt and promote generally applicable and discipline specific operating procedures, guidelines, and regulations accepted as best practices. |
Simple Rules may be simple to state …..
… but not always simple to follow.
Example: | Mechanistic MSM for cortical hyperexcitability |
1. context clear? | We were interested in assessing variants of hyperexcitability in an exploratory manner. We therefore did not pre-define a clear clinical context but left ourselves open to exploration of cortical activation for dystonia and seizures. |
2. appropriate data? | Data used to develop the model was taken from a large number of sources including different species, different preparations (slice, cell culture, in vivo, ex vivo), different age animals, different states, different conditions. None of the data was taken from the clinical disorders in question (limitations of human experimentation). |
3. within a context? | The model lacked the major output for dystonia validation, motor output, so could not be evaluated in proper context. Epilepsy context was somewhat more clear since based on cortical activity level. Beta activation in cortex was used as a dystonia evaluation surrogate. |
4. limitations explicit? | Model does not contain representations of spinal cord or limb. Model is lacking many relevant pharmacological parameters, particularly with respect to role of neuromodulators (known unknown), brain states (less known unknown) and metabolic parameters. |
5. version control | Mercurial (hg) used for all simulations as well as for paper and figure versioning |
6. documented? | Model available with README on ModelDB (189154). Partial parameter provenance and documentation available in manuscript. Full provenance database lacking. |
7. disseminated? | Model code on ModelDB available for manuscript reviewers on request. Model freely available after publication. Model and data disseminated via meetings. Manuscript published in open-source journal. Previous models have been used and modified by others. |
8. independent reviews? | This model was not reviewed by manuscript reviewers. Model was reviewed for run-capability on multiple platforms by ModelDB curator (Tom Morse) prior to release. |
9. competing implementations? | No other implementation attempted. Partially comparable implementations for epilepsy in neocortex do exist (e.g. Traub models, our prior models) and activity patterns could be compared. |
10. conformed to standards? | We conformed to standards for ModelDB submission and to best practice standards as taught in NEURON courses. Simulation workflows, data collection, data processing, data reporting conformed to practices generally accepted by the Computational Neuroscience community. |
| Neymotin SA, Dura-Bernal S, Lakatos P, Sanger TD, Lytton WW. Multitarget multiscale simulation for pharmacological treatment of dystonia in motor cortex. Frontiers in Pharmacology 2016 7:157. |
Example: | Phenomenological MSM: Virtual Brain (TVB) epileptor |
1. context clear? | Epilepsy in a specific group of patients. |
2. appropriate data? | Data from individual patient tractography and ECoG. |
3. within a context? | Comparisons with clinical results -- seizures |
4. limitations explicit? | Lack of explicit connections to cellular, metabolic or pharmacological scales |
5. version control | TVB is itself under git version control. |
6. documented? | yes |
7. disseminated? | papers, workshops, talks, posters |
8. independent reviews? | paper reviewed |
9. competing implementations? | unsure but the relative simplicity of model means could be coded in other ODE simulators |
10. conformed to standards? | TVB itself provides a standard for simulation at this scale |
| Proix T, Bartolomei F, Guye M, Jirsa VK. (2017) Individual brain structure and modelling predict seizure propagation. Brain. 140:641-654. |
Development of standards is a process
Community queried:
disparate groups
Additional references:
Peng GC. “Editorial: What biomedical engineers can do to impact multiscale modeling”. IEEE TBME, 58:3440-2, 2011.
McDougal RA, Bulanova AS and Lytton WW (2016). Reproducibility in Computational Neuroscience Models and Simulations. IEEE TBME. 63: 2021-2035.
Lytton WW (2017) Computers, causality and cure in epilepsy [Commentary on Brain 140:641]
Related Websites: www.asme.org/events/vandv (Mechanical engineers on V&V), journal.frontiersin.org/article/10.3389/fphar.2016.00157/full (Neymotin et al. paper), wiki.simtk.org/cpms (CPMS), www.ssih.org (Society for Simulation in Healthcare (primarily medical training)), cstools.asme.org/csconnect/CommitteePages.cfm?Committee=100108782 (med V&V), www.vph-institute.org (Virtual Physiological Human ), neuron.yale.edu (NEURON), modeldb.yale.edu (ModelDB), thevirtualbrain.org (Virtual Brain), neurosimlab.org (Downstate Neurosimulation Lab)
Neurosimulation Lab contributors: W Lytton, S Dura Bernal, S Angulo, A Newton, A Seidenstein, J Graham, M Sherif, RA McDougal (Yale), S Neymotin (Brown)
CPMS Executive Committee: A Erdemir, J Ku, L Mulugeta, L Tian, A Marsden, A Drach, C Hunt, D Eckmann, D Lochner, G An, G Pradhan, G Peng, J Bischoff, J Myers, M Horner, M Walton, M Steele, P Pathmanathan, R Vadigepalli, T Morrison, W Lytton
Neurosimulation Laboratory (SUNY, Downstate) and Committee on Credible Practice of Modeling & Simulation in Healthcare