OpenWorm
OpenWorm is an international open science project to simulate the roundworm Caenorhabditis elegans at the cellular level in silico. Although the long term goal is to model all 959 cells of the C. elegans, the first stage is to model the worm's locomotion by simulating the 302 neurons and 95 muscles cells. This bottom up simulation is being pursued by the OpenWorm community. So far the physics engine Sibernetic has been built and models of the neural connectome and a muscle cell have been created in the NeuroML format.[1] A 3D model of the worm anatomy can be accessed through the web via the OpenWorm browser. The OpenWorm project is also helping develop the Geppetto simulation framework.
Why simulate C. elegans?
C. elegans has the simplest brain with only 302 neurons. Furthermore, the structural connectome of these neurons is fully worked out. There are less than one thousand cells in the whole body of a C. elegans worm, each with a unique identifier and comprehensive supporing literature because C. elegans is a model organism. Being a model organism, the genome is fully known, along with many well characterized mutants readily available, a comprehensive literature of behavioural studies, etc. With so few neurons and new calcium 2 photon microscopy techniques it should soon be possible to record the complete neural activity of a living organism. By manipulating the neurons though optogenetic techniques, combined with the above recording capacities we are in an unprecedented position to be able to fully characterize the neural dynamics of an entire organism!
In trying to build an "in silico" model of a relatively simple organism like C. elegans, new tools are being developed which will make it easier to model more complex organisms.
Other Notable Attempts
In 1998 Japanese researchers announced the Perfect C. elegans Project. A proposal was submitted, but the project appears to have been abandoned.[2]
In 2004 a group from Hiroshima began the Virtual C. elegans Project. They released two papers which showed how their simulation would retract from virtual prodding.
In 2005 a Texas researcher described a simplified C. elegans simulator based on a 1-wire network incorporating a digital Parallax Basic Stamp processor, sensory inputs and motor outputs. Inputs employed 16-bit A/D converters attached to operational amplifier simulated neurons and a 1-wire temperature sensor. Motor outputs were controlled by 256-position digital potentiometers and 8-bit digital ports. Artificial muscle action was based on Nitinol actuators. It used a "sense-process-react" operating loop which recreated several instinctual behaviors. [3]
These early attempts of simulation have been criticized for not being biologically realistic. Although we have the complete structural connectome, we do not know the synaptic weights at each of the known synapses. We do not even know whether the synapses are inhibitory or excitatory. To compensate for this the Hiroshima group used machine learning to find the weights of the synapses which would generate the desired behaviour. It is therefore no surprise that the model displayed the behaviour, and it may not represent true understanding of the system.
NemaLoad
Project NemaLoad is a current research program which is trying to empirically establish the relevant biological facts which are necessary for a true bottom up simulation. The project founder, David Dalrymple, is a collaborator on the OpenWorm project.[4]
Open Worm Project
Although the ultimate goal is to simulate all features of C. Elegans behaviour, the project is new and the first behaviour the Open Worm community decided to simulate is a simple motor response: teaching the worm to crawl. To do so, the virtual worm must be placed in a virtual environment. A full feedback loop must be established from: Environmental Stimulus > Sensory Transduction > Interneuron Firing > Motor Neuron Firing > Motor Output > Environmental Change > Sensory Transduction ...
There are two main technical challenges here: modelling the neural/electrical properties of the brain as it processes the information and then modelling the mechanical properties of the body as it moves. The neural properties are being modeled by the Hodgkin Huxley equations, and the mechanical properties are being modeled by a Smoothed Particle Hydrodynamic algorithm.
The OpenWorm team built an engine called Geppetto which could integrate these algorithms and due to its modularity will be able to model other biological systems (like digestion) which the team will tackle at a later time.
The team also built an environment called NeuroConstruct which is able to output neural structures in NeuroML. Using NeuroConstruct the team reconstructed the full connectome of C. elegans.
Using NeuroML the team has also built a model of a muscle cell. Note that these models currently only model the relevant properties for the simple motor response: the neural/electrical and the mechanical properties discussed above.
The next step is to connect this muscle cell to the six neurons which synapse on it and approximate their effect.
The rough plan is to then both:
- Approximate the synapses which synapse on those neurons
- Repeat the process for other muscle cells
The official project milestones can be found here.
Open Science
The Open Worm community is committed to the ideals of open science. Generally this means that the team will try to publish in open access journals and include all data gathered (to avoid the file drawer problem. Indeed all the biological data the team has gathered is publicly available, and the five publications the group has made so far are available for free on their website. All the software that OpenWorm has produced is completely free and open source.
Open Worm is also trying a radically open model of scientific collaboration. The team consists of anyone who wishes to be a part of it. There are over one hundred "members" who are signed up for the high volume technical mailing list. Of the most active members who are named on a publication there are collaborators from Russia, Brazil, England, Scotland, Ireland and the United States. To coordinate this international effort, the team uses "virtual lab meetings" and other online tools while are detailed in the resources section.
Resources
Wiki This is where general information about the project goes. It is incomplete but a very useful primer for understanding the project. It also contains information on how to install and set up the software.
Github This is where the code is stored. Also it is a version control system for keeping track of changes to the code. There is also a well developed social networking aspect to the site. This is useful for following specific people and developing a reputation as a good developer. It is also used to post issues about the code and discuss them like a forum. It is also used to set and track goals for the project.
Blog This is where news stories or scientific articles which are relevant to the project or the team's interests are posted.
YouTube This is where software demonstrations and software tutorials are posted. There is also a very helpful [volunteer orientation video http://www.youtube.com/watch?v=vV7yKlE0VrE].
Every two weeks there is a "hang out" which takes place live on YouTube (and the Google+ page). These are opportunities for the OpenWorm community to talk "face to face", which is useful both for building a sense of community and also for keeping the project on track to reach its goals.
Every month there is a journal club "hang out", in which the OpenWorm community discusses a hot or relevant scientific paper.
Google+ and Twitter are another way the Open Worm team interface with the scientific community and the interested public.
Public Mailing List This is where most of the discussion happens. Anyone is free to post about anything.
References
- ^ http://www.openworm.org/downloads.html
- ^ http://www.jefftk.com/p/whole-brain-emulation-and-nematodes
- ^ P. Frenger, “Simple C. elegans Nervous System Emulator”, Houston Conf Biomed Engr Research, 2005, pg.192.
- ^ www.openworm.org/people.html