Thesis available

[Simon Schultz]

The following D.Phil. thesis is now available for downloading: 

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Information encoding in the mammalian cerebral cortex

Simon R. Schultz
Corpus Christi College, Oxford

Short abstract:

This thesis describes new techniques for studying information
encoding and transmission in the mammalian nervous system. The
underlying theme of the thesis is the use of information theory
to quantitatively study real and model neuronal systems. The
thesis begins with an analytical calculation of the information
that can be conveyed by a feedforward network of
threshold-linear neurons. The replica-symmetric solution for the
mutual information is found to be valid at all but low noise
values. This method is then used to make a quantitative
calculation of the information that can be conveyed by the
Schaffer collaterals, which project from hippocampal subregion
CA3 to subregion CA1. The effects on information transmission of
a number of details of the anatomy of the projection are
explored, including convergence, divergence and topography of
connectivity.

Information theory is then applied to the analysis of data from
neurophysiological recordings, by quantifying the information
encoded in the responses (action potentials) of neural ensembles
about environmental correlates. The decoding approach to
estimating the information contained in the responses of
populations of cells is examined in the limit of short time
windows. It is shown that in this physiologically pertinent
limit, decoding algorithms which estimate the full probability
distribution must fail, whereas maximum likelihood algorithms
remain accurate. The metric content, or amount of structure in
the neuronal activity, is found to have a residual component at
short time windows which is related to the instantaneous
information transmission rate. The equation for mutual
information is then approximated by a series expansion to second
order, and it is found that while as has been previously noted,
the first order terms depend only on the firing rates, the
second order terms break down into rate and correlational
components of the information. This leads to a new procedure for
quantifying the relative contributions of correlations (such as
synchronisation) and firing rates to neural information
encoding. The practicality of this procedure is demonstrated by
applying it to data recorded from the primate medial and
inferior temporal lobes.

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The thesis is available either as a gzipped postscript file:

http://www.mrc-bbc.ox.ac.uk/~schultz/thesis.ps.gz

or as individual chapters:

http://www.mrc-bbc.ox.ac.uk/~schultz/theschaps.html

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                            Simon Schultz                       
Department of Experimental Psychology                             also:
University of Oxford                             Corpus Christi College
South Parks Rd., Oxford OX1 3UD                          Oxford OX1 4JF
              
	    Phone: +44-1865-271419  Fax: +44-1865-310447 
                http://www.mrc-bbc.ox.ac.uk/~schultz/
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