Thursday, August 22, 2013

The Skin as a Social Organ: Part 1a: Touch can be pleasant, rilling.

The paper, The skin as a social organ

Previous introductory blogpost to this series.
Preamble: Random thoughts on spas

Part 1: Dual nature of touch: as PTs, do we "get" this?

The second and third statement in the abstract are really pretty self-evident. Aren't they? 
The second statement: 
"However, the research emphasis on these wide-ranging functions of touch leaves out a very essential fact: touch can also be pleasant." 

This is like a news flash to lots of manual therapists. They may well be touchphobes themselves (and if they are, who cares), but there is no excuse for ignoring this important information, clinically. Not when you're licensed to touch people, clinically. People who are in pain.
The third statement:
"This aspect of tactile sensation is at the heart of the social domain, allowing positive hedonic experience ranging from the reassurance of a pat on the back to the rills of a sensual caress."
Wasn't sure what a "rill" was. Thought maybe it was a Swedish word lost in translation. Or that somehow the word "thrilling" had been misspelled.
I looked it up, just to be sure, and... oh. my. gosh. It means some part of the landscape eroded by water, I think..  
(Look out, we may be in for yet another voyage, this time downstream.) 

Here is a picture of rills that caught my eye:

Rills on a cliff edge
They're lovely things, rills... they add texture to landscape. 
But rills can also be deliberately fashioned. I used to dig rills as a child, little drainage ditches with a toy shovel to carry meltwater away from the barn. My dad would nod his approval at my industrious efforts. 

I won't ever be able to go back to being a person who doesn't know what a rill is or what it means. Way more poetic than "neurotags"... don't you think? 

Apparently rills can be created in the brain by sensual caress. But probably any sort of well-intentioned touch in a carefully constructed context can do it, make metaphorical rills. As practitioners, let's not make any nociceptive rills. Let's not reinforce any that already are nociceptive. 

Next paragraph, only a few sentences long, but filled with a pile of references. 
Here we go, one sentence at a time:

"It is possible that functional divisions in the neural organization of touch may resemble that of pain, possessing two major, dissociable dimensions (e.g., Rainville et al. 1997; Hofbauer et al. 2001; Kulkarni et al. 2005; Auvray et al. 2008)." 
Rainville P, Duncan GH, Price DD, Carrier B, Bushnell MC (1997) Pain affect encoded in human anterior cingulate but not somatosensory cortex. Science 277:968–971 (Full text)
Hofbauer RK, Rainville P, Duncan GH, Bushnell MC (2001) Cortical representation of the sensory dimension of pain. J Neurophysiol 86:402–411 (Full text)
Kulkarni B, Bentley DE, Elliott R, Youell P, Watson A, Derbyshire SWG, Frackowiak RSJ, Friston KJ, Jones AKP (2005) Attention to pain localization and unpleasantness discriminates the functions of the medial and lateral pain systems. Eur J Neurosci 21:3133–3142 
Auvray M, Myin E, Spence C (2008) The sensory-discriminative and affective-motivational processing of pain. Neurosci Biobehav Rev. doi:10.1016/j.neubiorev.2008.07.008 (Full text)

 Wow, that is huge. I used to think that when I touched somebody on my treatment table I was touching their brain, all right, but only exteroceptively. Then I learned about C-fibres in skin whose job was to transmit pleasant input (from this group). We can touch peoples' interoceptors too! 
Next sentence:

"The sensory-discriminative dimension supports spatial localization and intensity encoding of a stimulus, and the motivational-affective dimension is involved in coding its valence (e.g., pleasantness/unpleasantness) and motivational relevance. So far, only a handful of studies have explored the possibility of a similar functional dissociation in the domain of non-painful cutaneous sensation (McGlone et al. 2007; Lovero et al. 2009)."
McGlone F, Vallbo AB, Loken L, Wessberg J (2007) Discriminative touch and emotional touch. Can J Exp Psych 61:173–183 
Lovero KL, Simmons AN, Aron JL, Paulus MP (2009) Anterior insular cortex anticipates impending stimulus significance. Neuroimage 45:976–983
Goodness, I shall have to hunt all these down, crack them open, take a look-see. For sure, that Lovero paper will be interesting. I think my anterior insular cortex tries to run my whole life. And she's very touchy. And by touchy, I mean picky.. 

"Though discriminative aspects of touch have been well-studied, the affective aspects have only recently been conceptualized and investigated in the neuroscientific literature (Essick et al.1999; Francis et al. 1999; Olausson et al. 2002; McGlone et al. 2007; Olausson et al. 2008a, b; Gallace and Spence 2008; Lovero et al. 2009; Löken et al. 2009; Guest et al. 2009)" 

Essick GK, James A, McGlone FP (1999) Psychophysical assessment of the affective components of non-painful touch. Neuroreport. 10:2083–2087 
Francis S, Rolls ET, Bowtell R, McGlone F, O’Doherty J, Browning A, Clare S, Smith E (1999) The representation of pleasant touch in the brain and its relationship with taste and olfactory areas. Neuroreport 25:453–459 (Full text)
Olausson H, Lamarre Y, Backlund H, Morin C, Wallin BG, Starck G, Ekholm S, Strigo I, Worsely K, Vallbo A˚ B, Bushnell MC (2002) Unmyelinated tactile afferents signal touch and project to insular cortex. Nat Neurosci 5:900–904 (Full text)
(This Olausson 2002 paper made my insular cortex go through the roof when I/we first laid eyes on it, about a decade ago.. 
"There!" it said, ".. there - do you believe me now!!??" 
"Yes," I replied. "Yes, I believe you.")
McGlone F, Vallbo AB, Loken L, Wessberg J (2007) Discriminative touch and emotional touch. Can J Exp Psych 61:173–183  
Olausson H, Wessberg J, Morrison I, McGlone F, Vallbo A (2008a) The neurophysiology of unmyelinated tactile afferents. Neurosci Biobehav Rev. doi:10.1016/j.neubiorev.2008.09.011 
Gallace A, Spence C (2008) The science of interpersonal touch: an overview. Neurosci Biobehav Rev. doi:10.1016/j.neubiorev. 2008.10.004 
Lovero KL, Simmons AN, Aron JL, Paulus MP (2009) Anterior insular cortex anticipates impending stimulus significance. Neuroimage 45:976–983 
Löken LS, Wessberg J, Morrison I, McGlone F, Olausson H (2009) Coding of pleasant touch by unmyelinated afferents in humans. Nat Neurosci 5:547–548 
Guest S, Essick G, Dessirier JM, Blot K, Lopetcharat K, McGlone F (2009) Sensory and affective judgments of skin during inter- and intrapersonal touch. Acta Psychol (Amst). 130:115–126

OK, two posts in one day, AND I got work done on the presentations. Not bad. I don't feel overly guilty now.

One more paragraph in the introduction, coming up next time. 

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