[Comp-neuro] Re: (1) Maybe channel biophysics is not the "real" level for analysis of brain function.

james bower bower at uthscsa.edu
Fri Aug 22 00:30:33 CEST 2008


jim

and nice to have engaged you again in this debate as well -- ah the  
old days -- anyway. Just one technical point (perhaps to make a larger  
point).

>

As you know, PSTHs are a statistical device derived from point process  
statistics whose central assumption is stationarity, thus your  
carefully added caveat " sometimes get approximate statistical  
consistency this way, sometimes not. "  A second assumption, the  
points (or action potentials) occur completely independent from each  
other as independent samples of the underlying process.

So, how appropriate really is this statistics to a device whose  
dynamical behavior is "held in the biochemical states of its neurons,  
developed through environmental experience, as they behave in complex,  
dynamically shifting networks."  And how much is this a leap of faith?

Which leads me to the following bit of history -- as a postdoc, I  
developed a technique (in Llinas' lab) to record from multiple (32)  
cerebellar climbing fibers at once -- I took that data to Wisconsin  
and to a wonderful mathematician named Josh Chover, and asked him how  
the heck to analyze this data.  He and I ended up teaching a course  
(in 1982) on multi-neuron data analysis (A guy named Matt Wilson was  
the TA).  During the course,   i realized that not only PSTHs but also  
correlation analysis (still the mainstay of this type of data  
presentation), was completely inappropriate - Despite taking multiple  
statistical courses as an undergraduate, I also finally realized the  
critical connection between the assumptions of the model from which  
any particular statistics is constructed (point process statistics) ,  
and the organization of the system to which they were applied  
(neuronal firing patterns).  Faced with the realization that point  
process statistics was completely inappropriate to analyze neuronal  
firing patterns - I asked myself, "what is the appropriate model from  
which to extract statistics to study the brain?" -- I decided that, in  
the limit, that model was the brain itself -- which is the original  
origin of my interest in building realistic models.  I convinced Matt  
Wilson to build a model of the olfactory cortex (over my supervisor  
Lew Haberly's objections), Matt came to Caltech where I bullied him  
into building the framework for GENESIS (to which he has never  
returned) -- and the rest, as they say is (if we are lucky) history.

So, I actually believe that the process of building analytical  
infrastructure around realistic models, is really the process of  
building statistical devices to keep shaping the models based on  
biological data.  And, I am suspicious of any level of modeling or  
analysis that relies on more generalized statistical models (like  
point process statistics).

Jim






==================================

Dr. James M. Bower Ph.D.

Professor of Computational Neuroscience

Research Imaging Center
University of Texas Health Science Center -
-  San Antonio
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