Dissertation abstract & Technical report

[menon@cs.utexas.edu]

 Technical report announcement:  

        Dynamic Aspects of Signaling in Distributed Neural Systems

                         Vinod Menon
                  Dept. of Computer Sciences 
                   Univ. of Texas at Austin 
                      Austin, TX 78712 

                          ABSTRACT 

  A distributed neural system consists of localized populations of
neurons -- neuronal groups -- linked by massive reciprocal
connections. Signaling between neuronal groups forms the basis of
functioning of such a system. In this thesis, fundamental aspects of
signaling are investigated mathematically with particular emphasis on
the architecture and temporal self-organizing features of distributed
neural systems.

Coherent population oscillations, driven by exogenous and endogenous
events, serve as autonomous timing mechanisms and are the basis of one
possible mechanism of signaling.  The theoretical analysis has,
therefore, concentrated on a detailed study of the origin and
frequency-amplitude-phase characteristics of the oscillations and the
emergent features of inter-group reentrant signaling.

 It is shown that a phase shift between the excitatory and inhibitory
components of the interacting intra-neuronal-group signals underlies
the generation of oscillations. Such a phase shift is readily induced
by delayed inhibition or slowly decaying inhibition. Theoretical
analysis shows that a large dynamic frequency-amplitude range is
possible by varying the time course of the inhibitory signal.

Reentrant signaling between two groups is shown to give rise to
synchronization, desynchronization, and resynchronization (with a
large jump in frequency and phase difference) of the oscillatory
activity as the latency of the reentrant signal is varied.  We propose
that this phenomenon represents a correlation dependent non-Boolean
switching mechanism. A study of triadic neuronal group interactions
reveals topological effects -- the existence of stabilizing (closed
loop) and destabilizing (open loop) circuits.

The analysis indicates (1) the metastable nature of signaling, (2)
 the existence of time windows in which correlated and uncorrelated
activity can take place, and (3) dynamic frequency-amplitude-phase
modulation of oscillations.  By varying the latencies, and hence the
relative phases of the reentrant signals, it is possible to
dynamically and selectively modulate the cross-correlation between
coactive neuronal groups in a manner that reflects the mapping
topology as well as the intrinsic neuronal circuit properties. These
mechanisms, we argue, provide dynamic linkage between neuronal groups
thereby enabling the distributed neural system to operate in a highly
parallel manner without clocks, algorithms, and central control.



 To obtain a copy of the technical report TR-90-36 please send 
$5 in US bank check or international money order payable to 
"The University of Texas" at the following address: 

Technical Report Center
Department of Computer Sciences
University of Texas at Austin
Taylor Hall 2.124
Austin, TX 78712-1188 USA

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Dept. of Computer Sciences                   email: menon at cs.utexas.edu 
University of Texas at Austin                tel:   512-343-8033
Austin, TX 78712                                       -471-9572
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