Abstract
. When gently stroked with velocities between 0.1 and 30 cm/s, participants typically rate velocities around 3 cm/s as most pleasant, and the ratings follow an inverted u-shape. This pleasantness curve correlates often, but not always, with the firing rate of unmyelinated C-tactile (CT) afferents, leading to the notion that CT afferents code for the hedonic or emotional aspect of gentle touch. However, there is also evidence that CT firing does not necessarily equal pleasantness, and the range of attributes that CT afferents code for is not known. Here, participants were stroked with different velocities assumed to activate CT afferents to a different extent while they rated the touch on several sensory and emotional attributes. We expected an inverted u-shaped rating curve for pleasantness and other emotional attributes, but not for sensory attributes. Inverted u-shaped rating patterns were found for the emotional attributes “pleasant” and “not burdensome,” but also for the sensory attribute “rough.” CT-directed stimulation is thus not only experienced as hedonic. The sensations arising from CTs together with all other types of mechanoreceptors might be centrally integrated into a percept that represents those aspects which are most salient for the stimulation at hand.
Highlights
The role of the so-called C-tactile (CT) afferents in touch perception has gained increasing attention
The firing rate of myelinated afferents increases with the speed of stimulation, and a positive quadratic regression model appears to provide the best fit (Ackerley, Backlund Wasling, et al, 2014; Loken et al, 2009)
Just as the firing rate of CTs, ratings of subjective pleasantness are maximal for velocities between 1 and 10 cm/s and follow an inverted u-shaped pattern (Ackerley, Backlund Wasling, et al, 2014; Loken et al, 2009)
Summary
The role of the so-called C-tactile (CT) afferents in touch perception has gained increasing attention These unmyelinated afferents can be found in the hairy skin of mammals and have a slow conduction velocity of about 0.9 m/s (e.g., Johansson et al, 1988; Vallbo et al, 1999; Watkins et al, 2017). Just as the firing rate of CTs, ratings of subjective pleasantness are maximal for velocities between 1 and 10 cm/s and follow an inverted u-shaped pattern (Ackerley, Backlund Wasling, et al, 2014; Loken et al, 2009). It seems likely that the perception of pleasant touch depends on the integration of input from both myelinated and unmyelinated afferents (see Vallbo et al, 2016)
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