The Journal of Neuroscience, November 1, 2002, 22(21):9556-9566
Neural Coding of the Location and Direction of a Moving Object by
a Spatially Distributed Population of Mechanoreceptors
Robert M.
Friedman,
Partap S.
Khalsa,
Kenneth W.
Greenquist, and
Robert H.
LaMotte
Department of Anesthesiology, Yale University School of Medicine,
New Haven, Connecticut 06520-8051
A neural code for the location and direction of an object moving
over the fingerpad was constructed from the responses of a population
of rapidly adapting type I (RAs) and slowly adapting type I (SAs)
mechanoreceptive nerve fibers. The object was either a sphere with a
radius of 5 mm or a toroid with radii of 5 mm on the major axis and
either 1 or 3 mm on the minor axis. The object was stroked under
constant velocity and contact force along eight different linear
trajectories. The spatial locations of the centers of activity of the
population responses (PLs) were determined from nonsimultaneously
recorded responses of 99 RAs and 97 SAs with receptive fields spatially
distributed over the fingerpad of the anesthetized monkey. The PL at
each moment during each stroke was used as a neural code of object
location. The angle between the direction of the trajectory of the PL
and mediolateral axis was used to represent the direction of motion of
the object. The location of contact between the object and skin was
better represented in SA than in RA PLs, regardless of stroke direction or object curvature. The PL representation of stroke direction was
linearly related to the actual direction of the object for both RAs and
SAs but was less variable for SAs than for RAs. Both the SA and RA
populations coded spatial position and direction of motion at acuities
similar to those obtained in psychophysical studies in humans.
Key words:
direction; location; movement; cutaneous afferent; fingerpad; mechanoreceptor
Copyright © 2002 Society for Neuroscience 0270-6474/02/22219556-11$05.00/0