Journal of Neuroscience, Vol 7, 2181-2191, Copyright © 1987 by Society for Neuroscience
Sinusoidal movement of a grating across the monkey's fingerpad: temporal patterns of afferent fiber responses
JW Morley and AW Goodwin
Responses were recorded from cutaneous afferents innervating
mechanoreceptors in the monkey's fingerpad, while gratings of alternating
grooves and ridges were moved sinusoidally across their receptive fields.
The gratings were specified by their spatial period and the movement by its
peak speed: together these determined the peak temporal frequency at which
grating ridges passed over the receptive field. During the central 42
degrees of each half cycle of movement, the speed and thus the temporal
frequency of the grating ridges remained constant to within 6.6% of their
peak values. In this region the responses of all afferents were
phase-locked to the temporal sequence of grating ridges. The number of
impulses elicited by each grating ridge was a function of the stimulus
variables. For all 3 afferent classes--namely, slowly adapting afferents
(SAs), rapidly adapting afferents (RAs), and Pacinian afferents (PCs)--the
number of impulses per grating ridge increased as the spatial period of the
grating increased (while the peak speed of movement was held constant).
Similarly, for all 3 classes, the number of impulses per ridge decreased as
the peak speed of movement increased (while the spatial period of the
grating remained constant). When the peak temporal frequency of the grating
ridges was held constant, for SAs and RAs the number of impulses per ridge
increased with an increase in the spatial period of the grating and thus
with an increase in the peak speed. These phase-locked responses provided
information about the peak temporal frequency of the grating ridges
independent of the grating spatial period and of the peak speed of
movement. The shape of the response profile during a half cycle of movement
was different for different afferents. Many of the RA response profiles
were close to sinusoidal. The SA and PC profiles tended to have reduced
peaks or raised troughs, resulting in flatter profiles. Other departures
from sinusoidal profiles were also seen.
Previous Article | Next Article
