Population estimates for responses of cutaneous mechanoreceptors to a vertically indenting probe on the glabrous skin of monkeys (original) (raw)
1993, Experimental Brain Research
Recordings were obtained from low-threshold mechanoreceptive afferents during stimulation with a 0.5-mm-diameter probe at the receptive field (RF) center and at different distances from the point of maximal sensitivity. At each location, force-controlled stimuli of 0.5-4.0 g were ramped on to a plateau and then off at rates of 1, 10, and 100 g/s. The properties of rapidly adapting (RA) and slowly adapting type I (SAI) mechanoreceptors, when stimulated at the RF center, were similar in many respects to those reported in previous studies. Controlled stimulation away from the RF centers revealed that RF size for RAs was primarily dependent upon ramp rate, and for SAIs the size of the RF was primarily dependent upon load (force). The action potentials from individual afferents during stimulation at each location were binned in time and assigned to spatial segments of 1 mm. These responses were multiplied by: (A) an annular area of the receptive field and (B) the innervation density for the afferent type and skin region. The calculations provided estimates of overall rates of activity among the population of cutaneous afferents that respond to indentation by a small probe. Important differences were obtained between the responses of the population of afterents activated by the trapezoidal stimulus and the responses of afferents stimulated only at the RF center. Populations of tactile afferents provide more information for rate and intensity (force) discriminations than is available from units stimulated at the RF center. For RA afferents, the exponent of the power function describing relationships between stimulus rate and the population discharge (in impulses per second) was 0.3 times greater than the exponent for responses to on-center stimulation. For SAI mechanoreceptors, the exponent of the power functions for static responses to force was 0.22 times greater for the population responses than for on-center activation. Population functions for RA responses to the rate of force application and for SAI responses to static load saturated less than comparable responses to stimu-Correspondence to: C.J. Vierck 106 fore, the relative magnitudes of onset, offset, and steadystate sensations elicited by stimulation at different rates and locations should vary systematically, according to the absolute and relative densities of each receptor type.
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Experimental Brain Research, 1970
The human capacity to scale the intensity of brief mechanical indentations of the hairy skin was measured by the method of subjective magnitude estimation. The afferent discharges evoked by nearly identical stimuli delivered to comparable locations on the hairy skin in monkeys were recorded in a number of types of fa'st-order mechanoreceptive afferents. It was shown that of these only those which adapt slowly to mechanical stimuli possess sufficient dynamic range of response to account for the range of human pressure sensation. Two such afferents innervating the hairy skin, previously identified by others as the Type I and Type II afferents, were studied in detail as regards their responses to brief mechanical stimuli of different intensities.
Properties of cutaneous mechanoreceptors in the human hand - related to touch sensation
Recordings from single peripheral nerve fibres made it possible to analyse the functional properties of tac-tile afferent units supplying the glabrous skin of the human hand and to assess directly the relation between impulse discharge and perceptive experiences. The 17,000 tactile units in this skin area of the human hand are of four different types: two fast adapting types, FA I and FA I1 (formerly RA and PC), and two slowly adapting types, SA I and SA 11. The receptive field characteristics and the densities in the skin of the type I units (FA I and SA I) indicate that these account for the detailed spatial resolution that is of paramount importance for the motor skill and the explorative role of the hand. The relationship between the stimulus amplitude and perceived intensity during sustained skin indentations did not match the corresponding stimulus response functions of SA units suggesting non-linear transformations within the central nervous system. These transformations, in turn, appear to vary between subjects. A single impulse in a single FA I unit may be felt when originating from the most important tactile regions of the hand, indicating that the psychophysical detection may be set by the threshold of the sense organs. Moreover, no significant noise seems to be superimposed in the respective central sensory pathways.
The neural signal for the intensity of a tactile stimulus
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1984
The effect of indenting the skin at different rates on the perceived intensity of the stimulus was studied by indenting the skin of the fingertip with two triangular waveforms, given as a pair. The subjects were asked to judge which member of the pair was more intense. Perceived intensity was found to increase both with the depth and the speed of the indentation. In contrast, changes in the rate of skin indentation had little influence on perceived skin indentation depth. This suggests that intensity and depth are different attributes of tactile sensibility. Since the skin is viscous, a rapid indentation is more forceful than a slow indentation of the same depth, raising the possibility that perceived intensity is related to stimulus force. Even though intensity judgments were more closely correlated with the force of a stimulus than with the indentation it produced, a rapidly increasing force was felt as more intense than one that increased more slowly but attained the same final m...
Quantitative Analyses of Dynamic Strain Sensitivity in Human Skin Mechanoreceptors
Journal of Neurophysiology, 2004
Edin, Benoni B. Quantitative analyses of dynamic strain sensitivity in human skin mechanoreceptors. . Microneurographical recordings from 24 slowly adapting (SA) and 16 fast adapting (FA) cutaneous mechanoreceptor afferents were obtained in the human radial nerve. Most of the afferents innervated the hairy skin on the back of the hand. The afferents' receptive fields were subjected to controlled strains in a ramp-and-hold fashion with strain velocities from 1 to 64% ⅐ s Ϫ1 , i.e., strain velocities within most of the physiological range. For all unit types, the mean variation in response onset approached 1 ms for strain velocities Ͼ8% ⅐ s Ϫ1 . Except at the highest strain velocities, the first spike in a typical SAIII unit was evoked at strains Ͻ0.5% and a typical SAII unit began to discharge at Ͻ1% skin strain. Skin strain velocity had a profound effect on the discharge rates of all classes of afferents. The "typical" peak discharge rate at the highest strain velocity studied was 50 -95 imp/s Ϫ1 depending on unit type. Excellent fits were obtained for both SA and FA units when their responses to ramp stretches were modeled by simple power functions (r 2 Ͼ 0.9 for 95% of the units). SAIII units grouped with SAII with respect to onset latency and onset variation but with SAI units with respect to dynamic strain sensitivity. Because both SA and FA skin afferents respond strongly, quickly, and accurately to skin strain changes, they all seem to be able to provide useful information about movement-related skin strain changes and therefore contribute to proprioception and kinesthesia.
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