The Journal of Neuroscience, April 15, 2000, 20(8):2934-2943
Extraction of Sensory Parameters from a Neural Map by Primary
Sensory Interneurons
Gwen A.
Jacobs1 and
Frederic E.
Theunissen2
1 Center for Computational Biology, Montana State
University, Bozeman, Montana 59717, and 2 Department of
Psychology, University of California, Berkeley, California 94720
We examine the anatomical basis for the representation of stimulus
parameters within a neural map and examine the extraction of these
parameters by sensory interneurons (INs) in the cricket cercal
sensory system. The extraction of air current direction by these
sensory interneurons can be understood largely in terms of the anatomy
of the system. There are two critical anatomical constraints. (1) The
arborizations of afferents with similar directional tuning properties
are located near each other within the neural map. Therefore, a
continuous variation in stimulus direction causes a continuous
variation in the spatial pattern of activation. (2) The restriction of
the synaptic connections of an interneuron to a unique set of afferents
results from the unique anatomy of that interneuron: its dendritic
arbors are located within restricted regions of the afferent map
containing afferents with a limited subset of directional
sensitivities. The functional organization of the set of four
interneurons studied here is equivalent to a Cartesian coordinate
system for computing the stimulus direction vector. For any air current
stimulus direction, the firing rates of the active interneurons could
be decoded as Cartesian coordinates by neurons at successive processing
stages. The implications of this Cartesian coordinate system are
discussed with respect to optimal coding strategies and developmental
constraints on the cellular implementation of this coding scheme.
Key words:
sensory maps; insect; functional neuroanatomy; sensory
interneurons; spatiotemporal patterns; neural coding
Copyright © 2000 Society for Neuroscience 0270-6474/00/2082934-10$05.00/0
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