Tip Stroking reveals pleasure nerve

[oljoha]

http://news.bbc.co.uk/2/hi/science/nature/7610383.stm

A new touch-sensitive nerve fibre responsible for the sense of pleasure experienced during stroking has been described at a UK conference today.

The nerves tap into a human's reward pathways, and could help explain why we enjoy grooming and a good hug, a neuroscientist has explained.

His team used a stroking machine to reveal the optimal speed and pressure for the most enjoyable caress.

The research was presented at the British Association Science Festival.

Mothers stroke their children, monkeys groom group members, and we all enjoy a massage, but what is it about stroking and rubbing that we find so enjoyable?

"People groom because it feels good," said Professor Francis McGlone, a cognitive neuroscientist at Unilever R&D, but went on to explain that little is known about how we experience the pleasure of touch.

In order to isolate the touch-sensitive nerves responsible for the pleasure experienced during stroking, Professor McGlone designed a "rotary tactile stimulator" - a high-tech stroking machine.

"We have built some very sophisticated equipment, so the stimulus [of stroking] is very repeatable.

"We stroke the skin [of the forearm, foreleg, and face] with a brush at different velocities, and then asked the volunteers to rate how they liked it," he explained.

He also inserted microelectrodes through the skin, into a nerve, to record the neural signals running from the skin to the brain.

"It is like tapping a single phone-line and listening for the chatter that comes down that line," he told the conference.

Feel-good chemicals

By comparing how the neural signals corresponded with how much the volunteers enjoyed the stroking, he was able to pin down people's pleasure to one set of nerves called "C-fibres".

He thinks that the stroking movements are activating C-fibres, which are wired into the rewards systems in the brain, causing the release of feel-good hormones.

Professor McGlone points out that these touch nerves are not responsible for the pleasure experienced from rubbing sexual organs, nor are they found in a person's palms or soles.

"Experiencing pleasure when grappling with tools or walking, would make both task difficult to do with any accuracy," he suggested.

The Liverpool-based researcher showed that stroking speeds of about 5cm per second, while applying 2g of pressure per square cm is optimal, and gave the volunteers most pleasure.

He explained that the pleasure messages are conveyed from the skin to the brain, by similar types of nerve fibres as those that transmit the sensation of pain.

"This is interesting as we often rub a pain to try to alleviate it," he said.

This could explain why the pain experienced by people exposed to a painful thermal stimulus, lessens when the region of the stimulus is simultaneously stroked.

Stroking could be used to treat chronic pain, he suggests.

[Diane]

I figured they would be properly found one day.

[Jon Newman]

Oljoha, great find. It looks like there is quite a bit of research on this. What do you think of the idea of "pleasure nerves" however? I only point this out because of the amount of time spent on describing the difference between nociceptive neurons and pain.

It's frustrating when those news reports don't cite a specific reference but here is one of many relevant abstracts from that scientist.

Can J Exp Psychol. 2007 Sep;61(3):173-83.Links
Discriminative touch and emotional touch.

McGlone F, Vallbo AB, Olausson H, Loken L, Wessberg J.
University of Liverpool.
Somatic sensation comprises four main modalities, each relaying tactile, thermal, painful, or pruritic (itch) information to the central nervous system. These input channels can be further classified as subserving a sensory function of spatial and temporal localization, discrimination, and provision of essential information for controlling and guiding exploratory tactile behaviours, and an affective function that is widely recognized as providing the afferent neural input driving the subjective experience of pain, but not so widely recognized as also providing the subjective experience of affiliative or emotional somatic pleasure of touch. The discriminative properties of tactile sensation are mediated by a class of fast-conducting myelinated peripheral nerve fibres--A-beta fibres--whereas the rewarding, emotional properties of touch are hypothesized to be mediated by a class of unmyelinated peripheral nerve fibres--CT afferents (C tactile)--that have biophysical, electrophysiological, neurobiological, and anatomical properties that drive the temporally delayed emotional somatic system. CT afferents have not been found in the glabrous skin of the hand in spite of numerous electrophysiological explorations of this area. Hence, it seems reasonable to conclude that they are lacking in the glabrous skin. A full understanding of the behavioural and affective consequences of the differential innervation of CT afferents awaits a fuller understanding of their function.

This related study looked interesting also.

Exp Brain Res. 2008 Jan;184(1):135-40. Epub 2007 Oct 26. Links
Functional role of unmyelinated tactile afferents in human hairy skin: sympathetic response and perceptual localization.

Olausson H, Cole J, Rylander K, McGlone F, Lamarre Y, Wallin BG, Krämer H, Wessberg J, Elam M, Bushnell MC, Vallbo A.
Department of Clinical Neurophysiology, Sahlgrenska University Hospital, Blå stråket 7, 413 45, Göteborg, Sweden. olausson@physiol.gu.se
In addition to A-beta fibres the human hairy skin has unmyelinated (C) fibres responsive to light touch. Previous functional magnetic resonance imaging (fMRI) studies in a subject with a neuronopathy who specifically lacks A-beta afferents indicated that tactile C afferents (CT) activate insular cortex, whereas no response was seen in somatosensory areas 1 and 2. Psychophysical tests suggested that CT afferents give rise to an inconsistent perception of weak and pleasant touch. By examining two neuronopathy subjects as well as control subjects we have now demonstrated that CT stimulation can elicit a sympathetic skin response. Further, the neuronopathy subjects' ability to localize stimuli which activate CT afferents was very poor but above chance level. The findings support the interpretation that the CT system is well suited to underpin affective rather than discriminative functions of tactile sensations.

[Diane]

It was from Olausson I first heard of the insula.
He had a paper in nature neuroscience about thin unmyelinated fibers that ended up in the insula. We have that paper here in S of S.
Sounds like he is to pleasure of somesthesis what Craig is to displeasure of somesthesis.

If anyone wants an entire book about fibers and how they connect to brain, and which bit of brain, get Sensory Hand by Mountcastle. I'm trying to go through that book carefully just now, page by page, but I get so excited I start jumping around through it.

[oljoha]

Originally Posted by Jon Newman

Oljoha, great find. It looks like there is quite a bit of research on this. What do you think of the idea of "pleasure nerves" however?

Pleasure is in the brain - not in the nerves.

[Jason Silvernail]

Saw the thread title and thought I'd wandered onto the wrong forum...

[oljoha]

Originally Posted by Jason Silvernail

Saw the thread title and thought I'd wandered onto the wrong forum...

It reminds me of a C64 game I saw when I was young:

http://www.lemon64.com/games/details.php?ID=2516 (BTW this link has an adult theme)

[Jason Silvernail]

Originally Posted by oljoha

(BTW this link has an adult theme)

Thanks for the thought, but this parenthetical statement is about the biggest "don't click here" I can think of.

Having had our fun, this is a really interesting piece of neuroscience.

[msaracen]

Ole,

It does look like a C64 game LOL. How did we get so old? I wonder if this "touch-sensitive nerve fibre responsible for the sense of pleasure" is the same as tickle? By tickle, I mean tickle feeling not like tickle your belly. Example, a moving probe going across the distal palmar crease (Hand) from radial to ulnar is quite a tickly feeling but not ticklish.

Mike

[Mary C]

Light stroking as described above (about 5cm/sec, 2 gm/cm2 pressure) is really paying off in the treatment of painful arthritis of the hands. I stroke from the shoulder to the wrist. Maybe this is why gentle lymph drainage techniques are also very effective at decreasing pain.

[Diane]

Light stroking as described above (about 5cm/sec, 2 gm/cm2 pressure) is really paying off in the treatment of painful arthritis of the hands. I stroke from the shoulder to the wrist. Maybe this is why gentle lymph drainage techniques are also very effective at decreasing pain.

Probably.