No subject

It provides compelling neurobiological evidence for the existence of 
stable attractor dynamics; at the same time, it forces consideration of 
the challenging problem of how to shift a stable activity profile.  
Because the first systematic experimental studies of HD cells were 
published only in 1990, the current paper includes a relatively complete 
reference list of the experimental publications, in addition to some 
immediately related theoretical papers.  

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The paper has appeared in:

	Journal of Neuroscience 16(6): 2112-2126 (1996)

Title: 	Representation of spatial orientation by the intrinsic
	dynamics of the head-direction cell ensemble: A theory

Author:	Kechen Zhang
	Department of Cognitive Science
	University of California, San Diego
	La Jolla, California 92093-0515

Abstract:

The head-direction (HD) cells found in the limbic system in freely moving 
rats represent the instantaneous head direction of the animal in the 
horizontal plane regardless of the location of the animal.  The internal 
direction represented by these cells uses both self-motion information for 
inertially based updating and familiar visual landmarks for calibration.  
Here, a model of the dynamics of the HD cell ensemble is presented.   
The stability of a localized static activity profile in the network and 
a dynamic shift mechanism are explained naturally by synaptic weight 
distribution components with even and odd symmetry, respectively.  Under 
symmetric weights or symmetric reciprocal connections, a stable activity 
profile close to the known directional tuning curves will emerge.   
By adding a slight asymmetry to the weights, the activity profile will 
shift continuously without disturbances to its shape, and the shift speed 
can be accurately controlled by the strength of the odd-weight component.  
The generic formulation of the shift mechanism is determined uniquely 
within the current theoretical framework.  The attractor dynamics of the 
system ensures modality-independence of the internal representation and 
facilitates the correction for cumulative error by the putative local-
view detectors.  The model offers a specific one-dimensional example of 
a computational mechanism in which a truly world-centered representation 
can be derived from observer-centered sensory inputs by integrating self-
motion information.  

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Comments and suggestions are welcome.
Email: zhang at salk.edu or kzhang at cogsci.ucsd.edu
http://www.cnl.salk.edu/~zhang