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Touch perceptions across skin sites: differences between sensitivity, direction discrimination and pleasantness.

Ackerley R, Carlsson I, Wester H, Olausson H, Backlund Wasling H - Front Behav Neurosci (2014)

Bottom Line: Human skin is innervated with different tactile afferents, which are found at varying densities over the body.The assessment of tactile pleasantness over the skin resulted in a preference for the middle velocities (1-10 cm s(-1)), where higher ratings were gained compared to the slowest and fastest velocities.This preference in tactile pleasantness was found across all the skin sites, apart from at the palm, where no decrease in pleasantness for the faster stroking velocities was seen.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Gothenburg Gothenburg, Sweden ; Clinical Neurophysiology, Sahlgrenska University Hospital Gothenburg, Sweden.

ABSTRACT
Human skin is innervated with different tactile afferents, which are found at varying densities over the body. We investigate how the relationships between tactile pleasantness, sensitivity and discrimination differ across the skin. Tactile pleasantness was assessed by stroking a soft brush over the skin, using five velocities (0.3, 1, 3, 10, 30 cm s(-1)), known to differentiate hedonic touch, and pleasantness ratings were gained. The ratings velocity-profile is known to correlate with firing in unmyelinated C-tactile (CT) afferents. Tactile sensitivity thresholds were determined using monofilament force detection and the tactile discrimination level was obtained in the direction discrimination of a moving probe; both tasks readily activate myelinated touch receptors. Perceptions were measured over five skin sites: forehead, arm, palm, thigh and shin. The assessment of tactile pleasantness over the skin resulted in a preference for the middle velocities (1-10 cm s(-1)), where higher ratings were gained compared to the slowest and fastest velocities. This preference in tactile pleasantness was found across all the skin sites, apart from at the palm, where no decrease in pleasantness for the faster stroking velocities was seen. We find that tactile sensitivity and discrimination vary across the skin, where the forehead and palm show increased acuity. Tactile sensitivity and discrimination levels also correlated significantly, although the tactile acuity did not relate to the perceived pleasantness of touch. Tactile pleasantness varied in a subtle way across skin sites, where the middle velocities were always rated as the most pleasant, but the ratings at hairy skin sites were more receptive to changes in stroking velocity. We postulate that although the mechanoreceptive afferent physiology may be different over the skin, the perception of pleasant touch can be interpreted using all of the available incoming somatosensory information in combination with central processing.

No MeSH data available.


Related in: MedlinePlus

Diagrammatic representations of the stroking stimuli and the tactile direction discrimination probe. (A) The rotary tactile stimulator, where a soft brush was stroked at precise velocities across each skin site and psychophysical ratings of pleasantness were gained. (B) The probe used for the tactile direction discrimination task, which was moved across the skin over specified distances.
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Figure 1: Diagrammatic representations of the stroking stimuli and the tactile direction discrimination probe. (A) The rotary tactile stimulator, where a soft brush was stroked at precise velocities across each skin site and psychophysical ratings of pleasantness were gained. (B) The probe used for the tactile direction discrimination task, which was moved across the skin over specified distances.

Mentions: A rotary tactile stimulator (Figure 1A; Dancer Design, Wirral, UK) was used to deliver controlled brush strokes at a predetermined force, direction and speed to the skin sites in question, using custom-written scripts in LabVIEW (National Instruments, Austin, TX). A moving soft brush was used as a pleasant stimulus (5 cm wide goat hair artists’ brush), where previous studies have shown that velocities around 1–10 cm s−1 are rated as more pleasant than slower or faster velocities (Löken et al., 2009, 2011). A total of five velocities (0.3, 1, 3, 10, 30 cm s−1) were tested three times per skin site, in a pseudo-randomized order. The stimulator was placed over the specific skin area, with the brush end centered approximately 2 cm above the skin. The force applied by the brush was calibrated to 0.4 N. The stroking was delivered in a proximal to distal direction, apart from on the forehead where it was from right to left. After each brush stroke was delivered, the participant rated the pleasantness of the sensation using a visual analog scale with the end anchors “Unpleasant” to the left and “Pleasant” on the right. There was a 10 s pause between strokes. The output from the scale ranged from −10 (unpleasant) to +10 (pleasant). Analyses were carried out on the averages of the three stroking repeats, giving five stroking velocity pleasantness data points per skin site, per participant. Stroking velocity was transformed to log10 values to improve the statistical inferences and interpretation, as in previous studies (Löken et al., 2009, 2011).


Touch perceptions across skin sites: differences between sensitivity, direction discrimination and pleasantness.

Ackerley R, Carlsson I, Wester H, Olausson H, Backlund Wasling H - Front Behav Neurosci (2014)

Diagrammatic representations of the stroking stimuli and the tactile direction discrimination probe. (A) The rotary tactile stimulator, where a soft brush was stroked at precise velocities across each skin site and psychophysical ratings of pleasantness were gained. (B) The probe used for the tactile direction discrimination task, which was moved across the skin over specified distances.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3928539&req=5

Figure 1: Diagrammatic representations of the stroking stimuli and the tactile direction discrimination probe. (A) The rotary tactile stimulator, where a soft brush was stroked at precise velocities across each skin site and psychophysical ratings of pleasantness were gained. (B) The probe used for the tactile direction discrimination task, which was moved across the skin over specified distances.
Mentions: A rotary tactile stimulator (Figure 1A; Dancer Design, Wirral, UK) was used to deliver controlled brush strokes at a predetermined force, direction and speed to the skin sites in question, using custom-written scripts in LabVIEW (National Instruments, Austin, TX). A moving soft brush was used as a pleasant stimulus (5 cm wide goat hair artists’ brush), where previous studies have shown that velocities around 1–10 cm s−1 are rated as more pleasant than slower or faster velocities (Löken et al., 2009, 2011). A total of five velocities (0.3, 1, 3, 10, 30 cm s−1) were tested three times per skin site, in a pseudo-randomized order. The stimulator was placed over the specific skin area, with the brush end centered approximately 2 cm above the skin. The force applied by the brush was calibrated to 0.4 N. The stroking was delivered in a proximal to distal direction, apart from on the forehead where it was from right to left. After each brush stroke was delivered, the participant rated the pleasantness of the sensation using a visual analog scale with the end anchors “Unpleasant” to the left and “Pleasant” on the right. There was a 10 s pause between strokes. The output from the scale ranged from −10 (unpleasant) to +10 (pleasant). Analyses were carried out on the averages of the three stroking repeats, giving five stroking velocity pleasantness data points per skin site, per participant. Stroking velocity was transformed to log10 values to improve the statistical inferences and interpretation, as in previous studies (Löken et al., 2009, 2011).

Bottom Line: Human skin is innervated with different tactile afferents, which are found at varying densities over the body.The assessment of tactile pleasantness over the skin resulted in a preference for the middle velocities (1-10 cm s(-1)), where higher ratings were gained compared to the slowest and fastest velocities.This preference in tactile pleasantness was found across all the skin sites, apart from at the palm, where no decrease in pleasantness for the faster stroking velocities was seen.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Gothenburg Gothenburg, Sweden ; Clinical Neurophysiology, Sahlgrenska University Hospital Gothenburg, Sweden.

ABSTRACT
Human skin is innervated with different tactile afferents, which are found at varying densities over the body. We investigate how the relationships between tactile pleasantness, sensitivity and discrimination differ across the skin. Tactile pleasantness was assessed by stroking a soft brush over the skin, using five velocities (0.3, 1, 3, 10, 30 cm s(-1)), known to differentiate hedonic touch, and pleasantness ratings were gained. The ratings velocity-profile is known to correlate with firing in unmyelinated C-tactile (CT) afferents. Tactile sensitivity thresholds were determined using monofilament force detection and the tactile discrimination level was obtained in the direction discrimination of a moving probe; both tasks readily activate myelinated touch receptors. Perceptions were measured over five skin sites: forehead, arm, palm, thigh and shin. The assessment of tactile pleasantness over the skin resulted in a preference for the middle velocities (1-10 cm s(-1)), where higher ratings were gained compared to the slowest and fastest velocities. This preference in tactile pleasantness was found across all the skin sites, apart from at the palm, where no decrease in pleasantness for the faster stroking velocities was seen. We find that tactile sensitivity and discrimination vary across the skin, where the forehead and palm show increased acuity. Tactile sensitivity and discrimination levels also correlated significantly, although the tactile acuity did not relate to the perceived pleasantness of touch. Tactile pleasantness varied in a subtle way across skin sites, where the middle velocities were always rated as the most pleasant, but the ratings at hairy skin sites were more receptive to changes in stroking velocity. We postulate that although the mechanoreceptive afferent physiology may be different over the skin, the perception of pleasant touch can be interpreted using all of the available incoming somatosensory information in combination with central processing.

No MeSH data available.


Related in: MedlinePlus