This part of the neuroanatomy of touch, or exteroceptive skin reception, of manual therapy contact, has been well worked out. According to Olausson and his colleagues, information from Ruffini endings in skin, which respond to lateral skin stretch, and will continue to fire as long as the stretch is continuously applied, travel along dorsal column pathways, and reach beyond S1 to dorsolateral prefrontal cortex. (4)
|Dorsal column pathways are fast. They go straight through to S1.|
The spinothalamic tract handles ascending traffic from thin, unmyelinated fibers. These fibers are "C" fibers. Nociceptors are among them, but C fibers are not restricted to only nociception. (1-5)
|These pathways are slow. They transmit nociceptive information, AND, also, pleasurable sensation.|
The main somatosensory map in the parietal cortex (S1) is non-judgemental - it records intensity only.
The affective network, the salience network, the threat-detecting "critter brain"(which includes the insular cortex and anterior cingulate cortex, part of the descending modulation/internal regulation system) is very judgey about contact. As manual therapists, if we know about this we can explain it to our patients so that when we touch them, they will be prepared in their "human" brain (4), for the contact we make with them. Then when we make that contact, they will be able to distance themselves from, or engage with, the sensations, as may be appropriate in the moment. They may even be better able to guide us, to help us help them better.
This is a picture of all the parts of the internal regulation system, and a description of its awesome powers. I call this the "critter brain." Our manual therapy should be mostly about helping patients win this part of their own brains over, in my opinion.
1. Löken LS; A Pathway for Pleasant Touch: Linking Peripheral Receptors To Central Processing And Hedonic Experience (thesis paper) U. Gothenburg, 2009
2. Morrison I; Reduced C-afferent fibre density affects perceived pleasantness and empathy for touch. Brain (2011)
3. Björnsdotter M, Morrison I, Olausson H; Feeling good: on the role of C fiber mediated touch in interoception. Exp Brain Res (2010) 207:149–155
4. Lundblad LC, Olausson HC, Malmeström C, Wasling HB; Processing in prefrontal cortex underlies tactile direction discrimination: An fMRI study of a patient with a traumatic spinal cord lesion. Neuroscience Letters 483 (2010) 197–200