[Comp-neuro] Re: Attractors, variability, noise, and other subversive ideas

james bower bower at uthscsa.edu
Tue Aug 19 17:23:21 CEST 2008

>  availability of source code is a necessary but but not sufficient
> condition.

I agree with this completely - while it is a good first step, without  
additional infrastructure, even with a common software platform (like  
GENESIS or NEURON or XPP) as a base, it is still difficult to figure  
these models out.  This is why I believe that text, graphics, and  
descriptions should be written around published models, rather than  
publishing models in a database unlinked and after publication of a  
written paper.  Model-DB is a good first step, but the infrastructure  
necessary to really publish models in a way that they can be  
understood (and improved on) by those that didn't built them, still  
needs to be constructed - and we are working on it.

Let me also comment on the issue of auto-review of published models --  
first, I am not suggesting that a submitted model can be completely  
autoreviewed -- while that may be a goal to strive for, for sure human  
review will continue to be an essential component of the review  
process for some time.  However, with model-based publishing, human  
review can be assisted with auto-review.  Here for example is a list  
of features of a model that could now be auto-reviewed.  I would love  
to have anyone else add to this list:

1) parameter ranges -- in single cell models everything from the  
conductance values of channels, to their voltage dependences can be  
evaluated and outliers identified. This function already exists in  
neuron and GENESIS in effect.  Auto-review could flag outliers for  
reviewers -- or authors for that matter  - who would then be under  
obligation to justify the unusual values.  This kind of analysis could  
also flag parameters that it is particularly important for next step  
experimental studies.

2) Certified (or previous used) components -- auto-review could  
identify components (channels, cell morphologies, etc) which are  
unchanged in the current model and have been approved through previous  
peer review - This evaluation could provide some more formal measure  
of what a new model has actually contributed that is new.  there is a  
risk here of course, of propagating bad assumptions -- but, on the  
other hand, this is potentially useful information -- in addition,  
this kind of auto-evaluation can be used to generate a lineage for a  
model.  How would it change tenure decisions or grant reviews, for  
example, if one had this kind of measure of "impact on the field".    
This measure could also help identify what is new

3) Robustness -- This is of course a major area of research in the use  
of numerical techniques, and can be expected to continue to develop --  
we need to be in a position, as a field, to take advantage of  
technical advances.  As auto-review, think of it as reverse parameter  
searching.  In some ways, evaluating what happens when you step  down  
the hill is easier than figuring out how to climb up it.   
Specifically, once a model is submitted,  we can (in principle) easily  
change key (needs to be defined) parameters by some percentage while  
remaining in the range of published values for the parameters, and  
evaluate the stability of core results.  In principle this is the kind  
of analysis that should be included in every model publication anyway,  
but seldom is - in fact, adding this as a feature of auto-review might  
very well push modelers to do more extensive (and quantitative)  
parameter sensitivity studies on their own.  Of course, there is an  
assumption here about how robust to parameter changes neurons and  
networks are in real life -- obviously, if there are some parameters  
that in real life have an inordinate effect on behavior, that is  
useful information to have as well, and leads directly to experimental  
questions.  As I already said, however, this area of parameter space  
testing and model evaluation can, of course, become quite complex,   
computationally intensive and is a subject of much core research in  
techniques for numerical simulation.

4) Completeness -- at present, there are cases I know of (not to my  
knowledge my own  :-)  ), where slightly different models were used to  
generate different figures in papers -- this is not necessarily  
intentional on the part of authors, as it is sometimes hard to keep  
track of versions of models (another thing that we are hoping to fix  
for GENESIS with 3.0).  Auto-review, by its nature, would assure that  
all figures are actually generated by the same model.

5) References -- if one has a system for annotating the antecedents  
for model components, in principle, one also has a way to check  
reference lists for omitted citations.

6) Minimal standards testing -- one could well imagine that for  
neurons or networks in general, or specific cases in particular, the  
field could agree on some minimal required ability for models -  
"generates an action potential", or "firing frequencies between 10 and  
100 Hz", or no dendritic back propagation (as is the case for Purkinje  
cells) against which all submitted models would be tested.  Again, one  
has to be aware that the current minimal standards might not be  
appropriate -- but simply identifying what they are, and testing  
models against them, would both help to standardize the field, and  
also provide a fixed target to argue for some other set of standards.   
Such a list would also be very useful for more abstracted models  
intent on capturing what the field considers to be essential features  
of more detailed models.  At present there are no standards of this  
sort for any kind of neural modeling that I am aware of.

These are all pretty straight forward to at least get started (are  
their others in this category? -- please suggest some).  More complex  
to develop, but in principle possible, and at the core of modeling are:

1) a more formal means of evaluating the relationship between real  
data and model output
2) a means of evaluating the advance made by a new model over previous  
3) a more formal means of comparing models

A formal mechanism to take either of these measures will almost  
certainly come out of the large ongoing research efforts involved in  
finding solutions to complex problems -- building the initial auto- 
review infrastructure will put us in a position to work on these more  
complex problems.

Again, if you have additions to this list, please send me a note, as  
we are building systems to start to do this.


On Aug 18, 2008, at 8:58 PM, Ross Gayler wrote:

>> By making his model source code freely available for years, Jim Bower
>> has actually been shoring up reproducibility in computational  
>> modeling.
>> It is hardly necessary to mention that reproducibility has elsewhere
>> been called a cornerstone of scientific method.
>> ...
>> To everyone who has published results obtained by studying  
>> computational
>> models of neurons or neural systems--at any level of abstraction--
>> free your source code!
> I couldn't agree more with the call for reproducible computational  
> research.
> However, availability of source code is a necessary but but not  
> sufficient
> condition.  There has been a steady thread of writing on reproducible
> research
> And associated tools over the last decade but it tends to be scattered
> across
> disciplines.
> http://www.reproducibleresearch.org/ provides pointers into some of  
> this
> literature.
> Fully reproducible research is something to aspire to.
> --Ross
> -----Original Message-----
> From: comp-neuro-bounces at neuroinf.org
> [mailto:comp-neuro-bounces at neuroinf.org] On Behalf Of Ted Carnevale
> Sent: Thursday, 14 August 2008 6:06 AM
> To: CompNeuro List
> Subject: Re: [Comp-neuro] Re: Attractors, variability, noise,and other
> subversive ideas
> james bower wrote:
>> This is one of the first times in history that a complex realistic  
>> model
>> has spread across labs and opinions -- and speaks very well for the
>> future - this is what the GENESIS project was about to begin with  
>> -- and
>> now, more than 20 years later, it is starting to happen, not only  
>> with
>> GENESIS but through Neuro-DB built by Michael Hines and the Neuron  
>> group
>> at Yale as well.
> Thanks for the plug, Jim.  And also for your advocacy of fresh ideas
> (whether I agree with all of them or not) in computational/theoretical
> neuroscience, or whatever it should be called.
> Allow me this minor typographical correction:  it's ModelDB.
> For those who may not yet know about it, here's the URL:
> http://senselab.med.yale.edu/modeldb/
> As of today, it contains source code for 394 published models,
> most of which is ready to run.  We invite authors of published
> models to submit them to ModelDB for attributed re-use and extension.
> Now for my own bit of advocacy--
> By making his model source code freely available for years, Jim Bower
> has actually been shoring up reproducibility in computational  
> modeling.
> It is hardly necessary to mention that reproducibility has elsewhere
> been called a cornerstone of scientific method.  How subversive of
> his own polemic is that?!
> As much as we might disagree on other issues, I am sure that Jim,
> and also Bard (who has likewise shared code freely) will join me in
> this call to arms:
> To everyone who has published results obtained by studying  
> computational
> models of neurons or neural systems--at any level of abstraction--
> free your source code!
> --Ted
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Dr. James M. Bower Ph.D.

Professor of Computational Neuroscience

Research Imaging Center
University of Texas Health Science Center -
-  San Antonio
8403 Floyd Curl Drive
San Antonio Texas  78284-6240

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