Diane
31-05-2008, 07:03 PM
I've added this post already in S of S (http://www.somasimple.com/forums/showthread.php?p=53430#post53430), but because I found a free version floating about on the internet, I decided to post here as well.
I thought this paper from the Canadian Journal of Experimental Psychology was very good:
Discriminative Touch and Emotional Touch (http://findarticles.com/p/articles/mi_qa3690/is_200709/ai_n21137497/print)
Abstract
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.
The paper argues a number of points, but the ones that I picked up on and agreed with were ones that highlighted the fact that two systems operate in the brain side by side and have their own opinions on what is or isn't important.
Discriminative decoding
1. Most tactile studies have been done on the discriminative system to SI (i.e., a less "emotional" decoder)
2. The discriminative system is mostly in the hands and lips (glabrous)
3. The hands (of monkeys) do not contain Ruffini receptors. But it looks like human hands do..
Emotional decoding
4. There is something very cool going on with Ruffinis, and it has to do with pleasurable social grooming
5. Contact of skin which is "Ruffini-ized" is more interoceptively interpreted than exteroceptively interpreted - i.e., different maps are accessed, and more non-conscious parts of the brain have more access than the more conscious, discriminating parts, parts that code for emotional content in the contact.
6. There are some C fibres that are decoded as having pleasure content, not just C-fibres that are decoded for having nociceptive content.
As manual therapists, we pretty much never handle lips or finger tips, do we? We are on the back of the trunk or head (i.e., little to no discriminative capacity, hardly any representation in the SI region of the cortex) and the limbs, sometimes the anterior of the trunk and neck, but still way less discriminative decoding capacity.
In other words, we are pretty much always on non-glabrous, no-discriminative, more emotionally decoded, interoceptively decoded skin receptors/body regions.
I like the suggestion that Ruffini's might contain some overlooked mystery, might be important for something - I've always thought so. :)
The c-fibres or interoceptors that convey info that can be decoded as pleasurable need a name. Maybe they could be called placeboceptors.
I thought this paper from the Canadian Journal of Experimental Psychology was very good:
Discriminative Touch and Emotional Touch (http://findarticles.com/p/articles/mi_qa3690/is_200709/ai_n21137497/print)
Abstract
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.
The paper argues a number of points, but the ones that I picked up on and agreed with were ones that highlighted the fact that two systems operate in the brain side by side and have their own opinions on what is or isn't important.
Discriminative decoding
1. Most tactile studies have been done on the discriminative system to SI (i.e., a less "emotional" decoder)
2. The discriminative system is mostly in the hands and lips (glabrous)
3. The hands (of monkeys) do not contain Ruffini receptors. But it looks like human hands do..
Emotional decoding
4. There is something very cool going on with Ruffinis, and it has to do with pleasurable social grooming
5. Contact of skin which is "Ruffini-ized" is more interoceptively interpreted than exteroceptively interpreted - i.e., different maps are accessed, and more non-conscious parts of the brain have more access than the more conscious, discriminating parts, parts that code for emotional content in the contact.
6. There are some C fibres that are decoded as having pleasure content, not just C-fibres that are decoded for having nociceptive content.
As manual therapists, we pretty much never handle lips or finger tips, do we? We are on the back of the trunk or head (i.e., little to no discriminative capacity, hardly any representation in the SI region of the cortex) and the limbs, sometimes the anterior of the trunk and neck, but still way less discriminative decoding capacity.
In other words, we are pretty much always on non-glabrous, no-discriminative, more emotionally decoded, interoceptively decoded skin receptors/body regions.
I like the suggestion that Ruffini's might contain some overlooked mystery, might be important for something - I've always thought so. :)
The c-fibres or interoceptors that convey info that can be decoded as pleasurable need a name. Maybe they could be called placeboceptors.