Sunday, September 01, 2013

The Skin as a Social Organ. Part 2c: The sad dearth of manual therapy aspects in reviews of interpersonal touch

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? Part 1a: Touch can be pleasant, rilling Part 1b: Vallbo on C-tactiles 

Part 2a: Different kinds of touch Part 2b: Proxemics


Next paragraph:
"Affiliative behavior is that which reflects or increases the disposition of one or more members in an interaction to seek close contact with another member. This is assumed to be accompanied by positive affective feelings, such as fondness, or with the alleviation of stress or anxiety. The motivational-affective dimension of social touch may provide mechanisms for the promotion of such positive consequences, ultimately pertaining to the desire to seek a touch (‘‘wanting’’) or to continue a tactile interaction (‘‘liking’’; see Berridge and Kringelbach 2008 for the ‘‘liking–wanting’’ distinction). Evidence that social touch encounters are accompanied by, and engender, positive affective consequences comes mainly from social psychological research investigating the relationship between interpersonal touch interactions and positive evaluations of  people and surroundings. These studies usually involve ‘‘simple’’ touch, though without designating it as such (hand-to-hand, hand-to-arm, hand-to-shoulder, etc.)."
Berridge KC, Kringelbach ML (2008) Affective neuroscience of pleasure: reward in humans and animals. Psychopharmacology (Berl) 199:457–480 [full text]

Full text! How handy. Berridge and Kringelbach ferret through all the neuroscience that has to do with "reward." They discuss three kinds: liking, wanting, and learning.

Liking: the actual pleasure component or hedonic impact of a reward.
Pleasure comprises two levels:
(1) core ‘liking’ reactions that need not necessarily be conscious;
(2) conscious experiences of pleasure, in the ordinary sense of the word, which may be elaborated out of core ‘liking’ reactions by cognitive brain mechanisms of awareness (see “A glossary of reward definitions” below for more detail on definitions).

Wanting: motivation for reward, which includes both
(1) incentive salience ‘wanting’ processes that are not necessarily conscious
(2) conscious desires for incentives or cognitive goals.

Learning: associations, representations, and predictions about future rewards based on past experiences.
Learned predictions include both
(1) explicit and cognitive predictions
(2) implicit knowledge as well as associative conditioning, such as basic Pavlovian and instrumental associations.

The thing that stands out for me right away whenever I read anything like this is the way researchers automatically classify everything into two baskets, core and conscious. I think the labels "critter brain" and "human brain" work reasonably well..

The authors continue:
"Of the three types of reward component, pleasure or hedonic ‘liking’ has probably been the least addressed in neuroscience studies. There is a special need for better understanding of how pleasure is generated by brain systems, and so we will focus particularly on pleasure in this paper."
They go on to explore the matter under the folowing headings:
From sensation to pleasure
Is human pleasure similar or different to that of other animals?
Pleasure coding versus causality
The consciousness of pleasure: can ‘liking’ ever be unconscious?
Pleasure generators: hedonic hotspots in the brain
Cortical cognition and pleasure
Orbitofrontal cortex: apex of pleasure representation?
Cortical causation of human pleasure?
Controversial subcortical pleasure generators? Dopamine and electrical brain stimulation
In what ways are the brain mechanisms of pleasure linked to human happiness?
It's quite a detailed paper. I very much appreciated the diagram of the orbiotfrontal cortex ("human" or at least part of prefrontal lobes of the brain) and all the ways it connects with "critter" brain.

Orbitofrontal cortex connectivity

These authors seem to think orbitofrontal cortex may well be a main train depot for loops that have to do with pleasure.
Morten Kringelbach
Pleasurable touch.

Kringelbach's entire mission in life seems to be to learn everything about pleasure in the brain that he possibly can in a single lifetime.
Here is a pubmed list of his publications.

Kent C Berridge

Kent Berridge is in Michigan, I think.
His list of publications in pubmed is longer still.

It looks as though these two have written an entire text, Pleasures of the Brain. 


In "A glossary of reward definitions" they lay out the distinctions. There are many. There is liking without quote marks, and "liking" with quote marks.
Liking (without quotation marks) Subjective hedonic reactions. This is the everyday sense of the word liking or pleasure, referring most directly to a conscious experience or subjective feeling of niceness.
‘Liking’ (with quotation marks) An objective hedonic reaction, measured behaviorally or neurally, whether or not accompanied by conscious pleasure. Core ‘liking’ reactions result from activity in identifiable brain systems that paint hedonic value on a sensation such as sweetness. Behavioral ‘liking’ reactions have been especially useful for mapping causal hedonic hotspots in the brain, particularly in the form of ‘liking’/‘disliking’ facial expressions to tastes that are homologous between humans and many other mammals. In humans, ‘liking’ reactions on their own have been shown in the form of unconscious pleasures, in cases where people remain unaware of an emotional stimulus and of their own hedonic reaction to it.

Likewise, wanting comes with and without quote marks:
Wanting (without quotation marks) The everyday sense of the word as a subjective desire. Conscious wanting typically is distinguished by requiring cortical mechanisms that generate declarative goals (based on memory or imagery): you want something in particular and may imagine it in advance of getting it. 
Wanting’ (with quotation marks) Incentive salience, a motivational process within reward that mirrors hedonic ‘liking’ and makes stimuli attractive when attributed to them by mesolimbic brain systems. Incentive salience is highly influenced by mesolimbic dopamine neurotransmission (though other neurotransmitters and structures also are involved). Importantly, incentive salience is not hedonic impact or pleasure. That is why one can ‘want’ a reward without necessarily ‘liking’ the same reward. Irrational ‘wanting’ without liking can occur via incentive sensitization in drug addiction, false pleasure electrodes, and similar cases because ‘wanting’ mechanisms are largely subcortical and separable from cortically mediated declarative expectation and conscious planning. Thus, for example, addicts may irrationally and compulsively ‘want’ to take drugs even if, at a more cognitive and conscious level, they do not want to do so.

So, basically, anything in the inner world of human experiential existence looks like it divides out into subjective first-person human brain perception with meaning assigned, and objective third-person critter brain observation.

Including pain. Except we have two words, nociception for objective observations of critter brain function, especially for when descending modulation is working fine, and pain for subjective human brain function, when it doesn't. Not that there isn't overlap. E.g., nociception feels "pain"-ful, at first anyway, shocking even, as when one cuts one's finger on a piece of paper or broken glass. Then it goes away. End of story. Pain is "sensed" as nociceptive input. But it can occur even when there is no part "hurting" or being "nociceptive." E.g., phantom limb pain.

A good trick in manual therapy is to always feel better than the person with whom you are working. Another way to say this, is never treat anyone who feels better than you do.

If you want to blow your mind on how easily somebody else's brain can pick up how you might happen to be feeling, even to the point of distinguishing 8 separate emotions, check out Matthew J. Hertenstein, Rachel Holmes, Margaret McCullough, Dacher Keltner; The Communication of Emotion via Touch. Emotion 2009, Vol. 9, No. 4, 566–573 [full text].

Also recommended: Living with Touch, by Alberto Gallace

Also recommended: Alberto Gallace, Charles Spence; The science of interpersonal touch: An overview. Neuroscience and Biobehavioral Reviews 34 (2010) 246–259

This is a review paper of nearly everything that has anything whatever to do with physical contact between humans. Glaringly absent from the paper is any mention of contact for therapeutic purpose. Not the authors fault - it's a review paper, and they reviewed whatever they could find. There ISN'T anything manual therapy-esque out there, for them to review, because no one in manual therapy thinks about or writes about it, yet, in any neuroscientifically scholarly manner for scholarly purposes. 

Not yet. 

Why is manual therapy not in this picture?

Manual therapy is still lumbering along like a big dumb robot under the illusion that it physically "does" "stuff" to "stuff." Maybe after it grows up a bit more, it will be able to justify its existence by way of neural mechanisms instead. But it won't happen in my lifetime, probably. I'll likely not live to see people like Gallace and Spence include scholarly manual therapy input into any review of interpersonal touch. The problem from the other side is that manual therapy continues to not be interested in studies of interpersonal touch, possibly because it doesn't see itself reflected in them or by them. 

Yeah, I know, I'm an oddball for concerning myself with matters like this. Who cares? I do! What a project though. Get neuroscience in under manual therapy. I must be crazy, right?
So be it. All I can do is complain about it, right now. 

Maybe someday things will change. I know Lorimer Moseley works hard, has madly laid groundwork, has taken on looking at pain, at least, from a neuroscientific perspective. Has published with several neuroscience people including Gallace and Spence. (See Moseley, GL, Gallace, A & Spence, C. (2008) Topical Review: Mirror Therapy: Is it all it is cracked up to be? Pain, 138(1) 7-10.)

So, faint rays of hope do shine through occasionally, into our self-made manual therapy dungeon of mesodoom. Even though there are wide heavy dark bars built from orthopaedic biomedicine, equally operative, third-person, equally deluded about "fixing" pain, by "fixing" tissue, or injecting it, or needling it, or ... oh, don't get me started, or I'll get off track over this. We'll be back to Skin as a Social Organ next time. 


1 comment:

Mark Hollis said...

'Get neuroscience in under manual therapy.' or even crazier 'Get manaul therapy in under neuroscience' and out or at least shared with the auspices of biomechanics.