GENESIS: Documentation

Related Documentation:

Question raised during initial development of Chemesis-3

0.1 2011/06/25: Writing custom G-3 extensions

It appears that the separation of a model into a biological component in the model container, and mathematical components in solvers can make the process of constructing new objects more difficult in G-3 than in G2. Can we minimize the complexity of this, while maintaining the structure of G-3?

response This may be the way it appears, but it is certainly not true. Because of the strict separation between the biological aspects of a model and their numerical representation, extension of G-3 is very different from extension of G-2 and requires many more steps. However, many of these steps can be automated and with the exercise of integrating Chemesis-3, we actually already automated some of them. We are currently looking for other solvers to be candidates for integration.

0.2 2011/06/25: Selective NDF_SAVE

Is there an option to ndf_save that will allow me to save only /cell? If not, can I give a model-container command from the gshell that is equivalent to the one used in conversions.t to generate simplecell-all.ndf?

What is the easiest way to extract the channel models to get .ndf files for the channels that appear in converted cell models? Of course, I could hand-edit the cell .ndf file to create ones for the each of the channels, and make a new NDF file for the cell that references the channels in the library, instead of having all the gate representations be in the cell file. But, there has to be a better way.

response This needs to be implemented.

0.3 2011/06/22: Browsing user documentation

I find it easier moving linearly through a users guide/tutorial, with occasionally being referred to another document for more in depth explanations. I don’t want to be sent to different places frequently.

response The documentation system has no layout algorithm yet that shows the narrative flows in which the displayed document participates.

0.4 2011/06/22: Types of user documentation

I would be tempted to create 2 (3) tutorial tracks:

response This has a relationship with the layers of the old G-2 users community. See the GENESIS overview.

0.5 2011/06/14: Morphology

morphology_summarize /Purkinje

and also this one:


but I’m not sure how that command works. I.e., why are spine_heads special? There is no morphology_list_branches. I would expect that spines are just additional compartments (at least I treat them that way in terms of calcium, etc.)

0.6 2011/06/14: Simulation Constants

runtime_parameter_show /Purkinje/segments/soma/cat G_MAX

As I suspected, you consider G_MAX a simulation constant and not a model constant. I am strongly opposed to this. G_MAX is no more a simulation constant than is tau, or V_half for a channel.

response When a parameter in the model-container is fixed to a value, it becomes a model parameter. But it is important to understand that the model-container does not make a rigid distinction between parameter and variables. For instance binding the same model parameter to the value of a variable, such as the membrane potential in a compartment, will turn it into a variable too. The solvers are responsible to recognize the variables in the model, or to emit an appropriate error message when the model is parameterized in a way beyond the solver’s capabilities.

0.7 2011/06/14: Event time tables

runtime_parameter_add /Purkinje/segments/branchlets/b1s06/b1s06[182]/Purkinje_spine_0/head/par/synapse EVENT_FILENAME event_data/events.yml

gives me no error message, even though I didn’t replace ”EVENT_FILENAME” with an existing filename. But I like this capability. This is what we use the time_table for in genesis 2. Is there more information on this capability?

response Currently not, but there are test cases for it in the gshell, see the test specification single_synapse.t and its html version. In the model library, the file ’event_data/events.yml’ is an example of an event file.

0.8 2011/06/14: Renaming a cell model

How to a load the cell model but give it a different name, or make an identical copy of a cell, and give it a different name?

response currently this can only be done by modifying the NDF file.

0.9 2011/06/14: Combining existing models

I would like to combine some of the gates in the NDF library to create additional channels (e.g., there are no recognizable calcium channels in the channels library), or modify some of the parameters to tailor the channels, but I don’t know how to do either of these. Which documentation would be most helpful for this?

0.10 2011/06/14: NDF for CHEMESIS-3

Note that the purpose of NDF is to maybe be readable, but not necessarily to verify or write. For most models I have worked with, it was actually human readable. For models that resulted after a conversion from G-2 it was unreadable to a human in most cases.

1. I see you have parameter thick, and then it’s commented out with //? so I’m not sure if you’re using it. I prefer having an outer and inner diameter or radius, to allow for shells, with the inner radius allowed to be zero for the inside shell. Then, the object itself can calculate thickness as well as all the needed surface areas. I suppose with thickness the inner diameter and all surface areas can be calculated, but I don’t see as they are existing fields in the pool object.

response This is an interesting question. The POOL component is already used for concentrations with exponential decay. Depending on the model it can use THICK and DIA (inferred from the parent segment) to compute BETA, and for other models it is convenient to specify BETA directly. Generally speaking the implementation of a component type can define convenience relationships between the different parameters. An trivial example is the relationship between a segment’s TAU, RM and CM. In the example I have used the same POOL model type that is used by the other models such as the Purkinje cell, the Traub model ao. I don’t know yet if this is a good idea.

2. I wouldn’t call the various pools substrate_somaCaBuf or product_somabuf. Though certainly that is how they act in the present simulation, all pools can simultaneously be substrates or products, so those names will be confusing as soon as the model is extended at all.

response these have been renamed. 3. I don’t understand the concept of groups, but I think I understand the concept of bindings - similar to messages? Are bindables just the inputs and outputs?

response Bindings are similar to messages in the sense that they define the mathematical connections (and also the topological connections) between model components. Bindings are available in the model-container. But during a simulation the solvers can decide to do something clever and not compute some of the variables. For instance, a compartmental solver does not have to compute an ion channel current, say soma/kdr-┐Ik, because it is not required to compute the membrane potential. However, when the user lists this current as a desired output, the compartmental solver can reconfigure itself to compute ion channel currents. This is what Heccer does (the current G-3 compartmental solver). This is of course dependent on how smart the implementation is.

A solver can also choose to compute variables that are not directly available from a model’s perspective. As an example the average membrane potential or calcium concentration of selected dendrites in a single time step can be computed. In G-3, you can tag model components, then tell Heccer to compute an average value of the tagged components.

Note that all these features work and are part of the automated test cases. The tagging is always available for new model components such as the reaction type.

4. On the other hand, I definitely do not understand the code following ”An extension file with the definition:” which means I wouldn’t be able to do additional development (though I suppose that comment is unfair given I’m still learning).

response Correct: you don’t have to write code to create a new type. In this case the configuration file mapped the reaction type to an already existing implementation. But of course it is possible to map to a new implementation and in this implementation code the logic specific to handle the parameters of that component. For example, the implementation of a segment defines the relationship between TAU, RM and CM and the implementation of a concentration pool defines the relationships between volume, diameter, thickness, valency and beta. If the reaction.yml would map a reaction type to the segment implementation, the new reaction type would know about TAU, RM and CM. Of course this is not what you want, but I am just illustrating the idea behind.

5. Related to groups, one of the nice things about NeuroRD is the ability to define a reaction independent of the morphology, and then the reaction occurs wherever there are the appropriate substrates. An good alternative for G-3 is to define a reaction independent of groups, and then specify which parts of the morphology it occurs in. In a large model, you don’t want to have to define 100 identical reactions, HOWEVER, that is what I did with G-2 - e.g. I looped through my 2D array of calcium pools, and created a 2D array of reactions (pseudo 2D since genesis doesn’t allow 2D arrays of elements).

calcium - the compartments must be much smaller than voltage compartments. So, it is necessary to subdivide each voltage segment or whatever you call them, into multiple calcium compartments. The calcium channels bridge these two compartments. I.e., each calcium compartment might have its own calcium channel, but each of these channels receives an identical voltage message. As an approximation, you could just take the calcium channel in the voltage compartment, and subdivide the current by the number of calcium compartments. However, using GHK to calculate driving potential, each of these calcium comp could have a different conc, e.g. if it had different synapses, and thus a different driving potential.

response The model-container allows to instantiate repetitive model components in different ways. It is possible to group arbitrary components and then to reference the group from many places. This does not necessarily mean that all (virtual) instances identified by these references must be mathematically identical.

As an example, the implementation of a segment defines the parameter SOMATOPETAL_DISTANCE (I might be wrong on the name of this parameter). The value of this parameter is dynamically inferred from the path to the soma. Using the notation ’..-┐DISTANCE’ in the definition of a reaction, pool or any other component allows to set the relationship of a parameter as dependent of its location in a morphology.

As I explained in my previous email, the model-container works with types (data) and algorithms. A second way of defining repetitive model components is to first declare 10000 identical model components then to randomize them (or do something else) using the algorithm specific for this purpose (it is called Randomize I believe, but have to look up again).

A third way of defining repetitive model components that is specific to reading morphologies, is to look at a parameter of a dendritic section in the morphology, for instance its diameter, and depending on the value of this parameter map the dendritic section to a predefined compartmental prototype. The compartmental prototype may have arbitrary complexity. The tool morphology2ndf implements this type of functionality, internally in the model-container it works with references to model components. Section 5 of explains this.

6. how to create a passive morphology - either specifying a few ”compartments” by hand or reading in a cell from, and how to create different ionic channels. Second step would be creating (or using if it exists) either GHK (for Ca channels) or Mg block (for NMDA channels).

7. The POOL token sounds like the old genesis ca_concen object. This is entirely not sufficient for doing general concentration pools. In particular, you absolutely cannot have any exponential decay. All decay is provided by various mechanisms. And you can’t have 2-D (or even 1-D) diffusion without additional geometry factors specified. By the time you add and remove stuff, you no longer have the old simple exp decay.

response The model-container stores all the different HH-channel types with the same CHANNEL token. This token is used for channels with activation, both activation and inactivation, and for channels with a concentration dependent gate. The CHANNEL implementation defines a derived parameter, called CHANNEL_TYPE that contains a value that changes dynamically with the number and type of HH-gates internal to the channel. This is convenient for a solver when it needs to allocate its internal structures, and it is convenient for a user when exploring a model.

The CHANNEL_TYPE parameter is dynamic in the sense that adding or removing a gate from a channel will change its value immediately. The value is never stored in memory.

The current implementation of the POOL token is exactly that: a pool of ions, whether exponential decay or with other dynamics. A modeler is assumed to think of a pool of ions, independent of whether its with simple decay, 1D or 2D diffusion. The parameterization of the pool token and its internal structure will define the behavior at simulation time.

Currently three different parameterizations of the POOL token will map it to one of the G-2 ca_concen object, the Chemesis-3 pool, or the Chemesis-3 conservepool objects.

For a user who is exploring a model, this means that querying the model for all concentration pools and then inspecing the parameters of the pools becomes trivial.

0.11 2011/06/14: Creation of the most simple simulations

If I wanted to create a single cell model with various channels. I discovered only a few synaptic channels and hodgkin-huxley channels. Then I looked at the introduction to ndf file format, which wasn’t too helpful, but was probably the best document, though still not sufficient. This shows me how to create a synaptic channel, but I don’t need another synaptic channel. Presumaly I can just take the existing ones and modify tau. It would be nice to see the ndf for a vdep channel, then I would better understand how to modify it to create other channels.

I must confess another command I really like is the listobjects commands in G2. I could see what existed, look at the fields and brief explanation of what it did. Also, I could look at the source code to figure out how it worked (I know that this latter step is done by almost noone.)

response The equivalent in the gshell of the G-2 listobjects command is ’help command create’. There are also commands with similar functionality: ’list structure’ list all tokens known to the model container to structure a model. As another example ’list physical’ lists all tokens knowns to the model-container that instantiate model components. There are a couple of other ’list ¡this and that┐’ commands, but they are of less interest here. After the tutorials, I still don’t know how to get started creating my own model, i.e.

1. how to define a simple morphology or read in a realistic one

2. how to add channels to various compartments

0.12 2011/06/14: Tests don’t pass on the regression tester. What now?

Then it is highly unlikely it will work on any other developer machine.

0.13 2011/06/08: Empty output when compiling the developer package???

That may wel be. ’make && sudo make install’ is the standard way of installing a Unix software package. Because the developer package is a minimal set of utilities, the ’make’ phase may be a no-operation depending on the revision of this package. The ’sudo make install’ is always required. Just continue with the installation of the other packages as explained in the documentation.

0.14 2011/06/03: Five ways to create simulations in GENESIS-3

0.15 2011/06/14: Tutorial 1

1. Instead of creating a cell called /n, I created one called /cell1 - so far so good. But, then later I forgot, and copied the tutorial commands ”output_add /n/soma Vm” and there were no complaints/error messages, even though I never created a /n object. It does give me an error when I try to run it, but not before then.

2. I can’t figure out how to examine the objects that exist for my use, or the fields/parameters in those objects. runtime_parameters_show shows me the parameters I created using that command (including my ”non_existent” parameter). model_parameter_show shows me parameters I’ve added. list_elements also helps, but I can’t examine the fields/parameters that already exist in the elements. Does that mean that I can add any parameter? That wouldn’t make sense, since parameters such as Rm act differently than parameters such as INJECT.

3. set_verbose warning doesn’t seem to be doing what it says, though set_verbose information does.

4. Are SI units required, or can I use any set of consistent units? FYI, I really hate being forced to use SI units, since my experiments and publications all report stuff using physiological units.

response Representation of parameter values in a user-chosen unit system is a User Interface issue. The gshell and its python based alternative will do the conversion from SI to other unit systems. The model-container and solvers always use SI units. This is to prevent specification of one model in different unit systems. Conversion between unit systems is a matter of multiplying and offsetting the values (when they are numeric). Dave has recently written a document about this and we should incorporate this type of functionality into the gshell such that a user can script a model using any unit system he likes, and the model-container will always see, store and provide SI based values to other components, including (G)UIs and solvers.

5. In the discussion of simulation constants (tutorial1), it seems you are claiming that conductance of the CaT channels is a sim constant and not a model constant, but I would strongly disagree. I think of the model as analogous to the tissue an experimentalist records from. conductances are definitely model parameters, where as dt, runtime, mesh element size, current injection are simulation parameters or simulation inputs.

6. Continuing with tutorial1, I tried

genesis > ndf_load /n myneuron.ndf

but it didn’t work:

Could not find file (number 1, 1), path name (/n)  
Set one of the environment variables NEUROSPACES_NMC_USER_MODELS,  
to point to a library where the required model is located,  
or use the -m switch to configure where neurospaces looks for models.  
*** Error: ndf_load /n

when I used the -m switch, nothing happened, and there was no help for this command.

7. In the tutorial, you suggest storing output in /tmp :

genesis > sh cat /tmp/output

but I would never want to write my output to that directory. also, how is that the default since you specify full path? I would think the default would be the directory from which you invoked genesis. Strangely, this command is not working today. I keep getting ”No such file or directory” no matter what filename or directory I specify. OK, I figured it out. In the tutorial discuss where simulation output is, and then give the sh cat command _before_ you present ”run simulation”. So, of course an error is returned. I recommend changing the tutorial so that the sh cat command is explained after the run simulation to prevent errors, or explain not to invoke the command till after running the model. Also, I would change the default location of the files, and explain how to specify a file location.

9. model_state_load doesn’t appear to work. I tried calling it two different ways:

genesis > model_state_load tempmodel  
*** Error: <modelname> and <filename> are required

genesis > model_state_load /n tempmodel  
HeccerConstruct: cannot find model /n  
/usr/local/bin/genesis-g3: While running GENESIS3 SSP schedule initiated for /n, 0: compile failed (error: HeccerConstruct() from the model_container failed) at /usr/local/glue/swig/perl/ line 1756.  
 at /usr/local/bin/genesis-g3 line 54  
       main::__ANON__(’/usr/local/bin/genesis-g3: While running GENESIS3 SSP schedul...’) called at /usr/local/glue/swig/perl/ line 1756  
       SSP::run(’SSP=HASH(0x2270958)’) called at /usr/local/glue/swig/perl/ line 1956  
       GENESIS3::Commands::run(’/n’, 0) called at /usr/local/glue/swig/perl/ line 1182  
       GENESIS3::Commands::model_state_load(’/n’, ’tempmodel’) called at (eval 50) line 1  
       eval ’GENESIS3::Commands::model_state_load( \’/n\’, \’tempmodel\’, )  
;’ called at /usr/local/bin/genesis-g3 line 171  
       main::interprete(’model_state_load /n tempmodel’) called at /usr/local/bin/genesis-g3 line 242  
       main::loop() called at /usr/local/bin/genesis-g3 line 307  
       main::main() called at /usr/local/bin/genesis-g3 line 367  
$Result = undef;  

0.16 2011/05/28: Customizing GENESIS-3 (1)

General question #1: Is this currently possible, or are there parts of the G-3 infrastructure that need to be implmented in order to make this task straightforward? At present, it seems to be a lot harder than extending G2, although in principle it should be easier. We also talked about a demo using Python scripting to show how G-3 can interoperate with an external Python script. In principle, this script could invoke PyMOOSE or PyNEURON and incorporate part of a model in one of these simulators, but I had something much simpler in mind. The simplest trivial case (which I would try first) would be a simple application that makes a graph like G3Plot, but gets the data directly from /cell/soma Vm as it runs, rather than from a file. The demo that I would like to write is an ”efield application” (not an added object) that works as I described in my ”Interoperability example” email, with a Python object that recieves compartment or channel currents as the simulation runs, calculates the extracellular potential, and sends it to a plot object.

0.17 2011/05/28: Customizing GENESIS-3 (2)

General question #2: What needs to be done to make this demo possible? Is it already possible to have a Python script access something like asc_file and get the output directly as it is generated? Are their any problems associated with getting the Ik values? I was not able to send Gk to an asc_file. The simplecell_spike_pulse.g in testchannels-0.9/simplecells was designed to be another example to convert to Python, but failed to run in ns-sli for many reasons.

0.18 2011/05/28: Customizing GENESIS-3 (3)

General question #3: I am still trying to get a clear idea of whether I should choose Python scripting, SLI backwards compatibility scripting, or basic G-shell scripting for this release.

0.19 2011/05/28: Customizing GENESIS-3 (4)

General question #4: Will scripting in G-3 Python (or anything else) preserve the GENESIS paradigm of elements coupled with ”messages”? In GENESIS 2 SLI, a ”message” is not the usual one-time event of other languages, but is more of a persistent data connection.

0.20 2011/05/21: an efield object

Suppose that I want to implement an efield object to measure the extracellular potential at some point outside a Purkinje or traub94 cell. It needs to know Ik in every compartment at specified intervals (probably much less than the simulation time step), and the coordinates of each compartment, in order to calculate the inverse square distance. This can be done by either (1) creating a G-3 object in C and making it available to gshell, ns-sli, or the Python interface; or (2) creating an external ”efield application” in Python that loads and runs the cell model and gets the needed information for its own Python efield object.

It is the second that I’m most interested in now, and that has the most relevance to the chapter I’m writing, but I’d like to think ahead to the first. When you can find the time, could you try to give me some general answers in terms of ”what things do I need to know about?” for these questions? Later, I may pin you down for names of example code files or specific documentation that exists.

1. If i write an efield object in C, using the vclamp or PulseGen code as an example

a. How do I make it availble to the gshell? I suspect that the docs genesis-extend-model-container will answer a lot of this. What else do I need to know about in order to be sure that the efield object gets the Ik information at specified intervals?

b. How would I make the new efield object accessible to a Python script, and use Python to set up the communication with the cell? This could be called interoperability of a sort, because Python is external to G-3. But it isn’t really what I mean by interoperability because it requires changes to G-3 to add a new object.

c. What is involved in doing this for ns-sli? Is it more or less work than doing it for Python?

2. As a demo of ”run-time interoperability” and a useful tool, I’d like to write a Python script that, as in (1b), would import nmc and heccer, then issue commands to load a cell model from a NDF file. But, it would implement its own efield object in Python.

a. Do we yet have a way to load a cell from a NDF file in Python? The cbi-scripting/scripting-example files just create and intialize a soma compartment. This would seem to be the next step.

b. How do I get the Ik information to the Python efield object in an efficient manner through the Python interface?

You can ignore question (1) for now. I posed it just to show the contrast. At some point I’ll need to create documentation on doing this, after trying it myself, but (2) is more important to me now, and I hope easier.