DORSAL HORN SPATIAL REPRESENTATION OF SIMPLE CUTANEOUS STIMULI
Paul B. Brown, Ronald Millecchia, Jeffrey J. Lawson, Stephanie Stephens, Paul
Harton and James C. Culberson.
Departments of Physiology and Anatomy, West Virginia University Health
Sciences Center, Morgantown, WV 26506.
APStracts 4:284N, 1997.
ABSTRACT
A model of lamina III-IV dorsal horn cell receptive fields (RFs) has been
developed in order to visualize the spatial patterns of cells activated by
light touch stimuli. Low threshold mechanoreceptive fields (RFs) of 551 dorsal
horn neurons recorded in anesthetized cats were characterized by location of
RF center in cylindrical coordinates, area, length/width ratio and orientation
of long axis. Best-fitting ellipses overlapped actual RFs by 90%.
Exponentially smoothed mean and variance surfaces were estimated for these
five variables, on a grid of 40 points mediolaterally by 20/segment
rostrocaudally in dorsal horn segments L4 - S1. The variations of model RF
location, area, and length/width ratio with map location were all similar to
previous observations. When elliptical RFs were simulated at the locations of
the original cells, the RFs of real and simulated cells overlapped by 64%. The
densities of cell representations of skin points on the hindlimb were
represented as pseudocolor contour plots on dorsal view maps and segmental
representations were plotted on the standard views of the leg. Overlap of
modeled and real segmental representations was at the 84% level. Simulated and
observed RFs had similar relations between area and length/width ratio and
location on the hindlimb: r (A) = 0.52; r (L / W) = 0.56. While the
representation of simple stimuli was orderly, and there was clearly only one
somatotopic map of the skin, the representation of a single point often was
not a single cluster of active neurons. When two-point stimuli were simulated,
there usually was no fractionation of response zones or addition of new zones.
Variation of stimulus size (area of skin contacted) produced less variation of
representation size (number of cells responding) than movement of stimuli from
one location to another. We conclude that stimulus features are poorly
preserved in their dorsal horn spatial representation, and discrimination
mechanisms which depend on detection of such features in the spatial
representation would be unreliable.
Received 15 July 1997; accepted in final form 14 October 1997.
APS Manuscript Number J585-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 29 October 1997