Four channels mediate the mechanical aspects of touch

Abstract

Although previous physiological and anatomical experiments have identified four afferent fiber types (PC, RA, SA II, and SA I) in glabrous (nonhairy) skin of the human somatosensory periphery, only three have been shown to mediate tactile (mechanoreceptive) sensation. Psychophysical evidence that four channels (P, NP I, NP II, and NP III) do, indeed, participate in the perceptual process is presented. In a series of experiments involving selective masking of the various channels, modification of the skin-surface temperature, and testing cutaneous sensitivity down to very low-vibratory frequencies, the fourth psychophysical channel (NP III) is defined. Based on these experiments and previous work from our laboratory, it is concluded that the four channels work in conjunction at threshold to create an operating range for the perception of vibration that extends from at least 0.4 to greater than 500 Hz. Each of the four channels appears to mediate specific portions of the overall threshold-frequency characteristic. Selection of appropriate neural-response criteria from previously published physiological data and correlation of their derived frequency characteristics with the four psychophysical channels indicates that each channel has its own physiological substrate: P channel and PC fibers, NP I channel and RA fibers, NP II channel and SA II fibers, and NP III channel and SA I fibers. These channels partially overlap in their absolute sensitivities, making it likely that suprathreshold stimuli may activate two or more of the channels at the same time. Thus the perceptual qualities of touch may be determined by the combined inputs from four channels.

Relation between vibrotactile perception thresholds and reductions in finger blood flow induced by vibration of the hand at frequencies in the range 8–250 Hz

“…Psychophysical studies have shown that with the contact conditions used in the current study the thresholds at these low frequencies are not mediated by the Pacinian channel but by another channel, probably NPI associated with Meissner corpuscles (Bolanowski et al, 1988). The four channel psychophysical model suggests that around 25 dB SL above the absolute thresholds for these frequencies, one or more other channel, including the P-channel, become activated and involved in the mediation of sensations (Bolanowski et al, 1988). The results suggest finger blood flow reduced when the vibration magnitude was sufficient to activate the Pacinian receptors, which occurs at threshold levels at high frequencies but at magnitudes much greater than the threshold at low frequencies.…”

“…Although thresholds at low frequencies are determined by the responses of a non-Pacinian channel, other mechanoreceptors become activated at greater magnitudes of vibration (Bolanowski et al, 1988;Verrillo et al, 2002). At vibration magnitudes 25, 30, and 40 dB SL above the threshold, the Pacinian channel is expected to have been activated.…”

“…Thresholds for perceiving vibration of the hand are determined by one or more of four psychophysical channels associated with mechanoreceptors in the glabrous skin of the hand (Bolanowski et al, 1988). The most sensitive channel depends on the frequency of the vibration, the contact conditions, the location on the hand, and some other factors.…”

“…The Pacinian (P) channel, mediated by Pacinian corpuscles (also called FA II units), has the lowest threshold at frequencies greater than about 40 Hz when using a 6-mm vibrating contactor (Morioka and Griffin, 2005;Morioka, et al, 2008), and exhibits both spatial and temporal summation: reduced thresholds with increased area of excitation and increased duration of vibration (Verrillo 1962(Verrillo , 1963. Of the three non-Pacinian channels, the NPI channel often determines thresholds at frequencies between 4 and 40 Hz and is associated with Meissner corpuscles (FA I units), whereas the NPII and NPIII channels are associated with slow adapting fibres and have been identified from the results of psychophysical experiments (Capraro et al, 1979, Bolanowski et al, 1988, Verrillo et al, 2002. The NPII channel, which is excited by vibration in the same frequency range as the Pacinian channel, is sensitive to the stretching of the skin and in most conditions has a higher threshold than the Pacinian channel (Bolanowski et al, 1988).…”

“…Of the three non-Pacinian channels, the NPI channel often determines thresholds at frequencies between 4 and 40 Hz and is associated with Meissner corpuscles (FA I units), whereas the NPII and NPIII channels are associated with slow adapting fibres and have been identified from the results of psychophysical experiments (Capraro et al, 1979, Bolanowski et al, 1988, Verrillo et al, 2002. The NPII channel, which is excited by vibration in the same frequency range as the Pacinian channel, is sensitive to the stretching of the skin and in most conditions has a higher threshold than the Pacinian channel (Bolanowski et al, 1988). The NPIII channel may have a lower threshold than other channels in the range 0.4 to 4 Hz (Greenspan and Bolanowski, 1996).…”