I do not think any of the above points can be ruled out, no matter what "kind" of manual therapy one was taught. Yet none of these considerations are commonly taught by current manual therapy institutions or teachers to my knowledge.
I found a paper lately, Processing in prefrontal cortex underlies tactile direction discrimination: An fMRI study of a patient with a traumatic spinal cord lesion.
"We have investigated cortical processing of tactile direction discrimination (TDD) in a patient with unilateral tactile disturbance due to spinal cord lesion. The patient R.A. (male, 45 years old), suffers from a traumatic dorsal column lesion at the level of Th XI-XII on the right side. He was instructed to report the direction of 2mm long skin pull stimulations applied in a proximal or distal direction on his right or left lower legs during functional magnetic resonance imaging (fMRI). Although R.A. considered himself to have nearly normal tactile sensibility, testing showed severely disturbed TDD on his right leg whereas results were within the range of healthy subjects on his left leg. For both legs TDD activated an extensive cortical network that included opercular parietal area 1 (OP1) of the second somatosensory cortex (S2), as has previously been observed in healthy subjects. However, dorsolateral prefrontal cortex (DLPFC) and anterior insular cortex (AIC) were only activated for the unaffected (left) leg where TDD was normal. A revisit of previously published data showed that healthy subjects consistently had TDD-related activations in DLPFC and AIC. However, in several healthy subjects AIC, but not DLPFC, was also activated for skin pull stimulations per se without the TDD task. Thus, the patient's data, in conjunction with the previous results from healthy subjects, suggest that DLPFC processing is important for tactile decision making based on proper tactile input."Their subject was an individual who had sustained a cord lesion two years prior (due to a mishap by a person providing him with epidural anesthesia for a colon operation). The lesion was at the level of T11-12, 12mm long and 2mm wide, to the right of the cord medulla, in the dorsal column. This left him with sensory deficit - the point of the study was to determine exactly what sort. He had right leg pain, and some difficulty running, although he could still run.
The authors used a device that could apply skin stretch (2 millimeters) in a directional, quantifiable manner, to hairy skin on the human leg, and looked at that was happening in the brain at the same time via fMRI. To the right is a picture of it. It went into the fMRI machine with him. They glued a 2-mm rod to the lower leg with which to pull the skin. The paper describes all the details of how the testing was conducted, how much, how long, how many times, etc.
From the paper:
"TDD for a high-friction stimulus (i.e. lateral skin pull stimulation) utilizes information about patterns of skin stretch [8,18] mainly signalled by a population of slowly adapting type 2 (SA2) afferents (commonly regarded as Ruffini afferents)"
|Could this be why skin stretching, or massage,|
or any 'kind' of manual therapy,
is often effective for reducing pain,
clinically, at least in the short term?
From the paper:
"The DLPFC has been reported to be involved in sensory decision making . In an fMRI study on a vibration discrimination task in healthy subjects it was found that the level of activity in the left DLPFC correlated to the accuracy of the perceptual decisions . Our results showed DLPFC activation only for the patient’s unaffected (left leg) where he was able to perceive the difference in movement direction in TDD and thus gave more correct answers. Further, we found reliable activation of DLPFC in healthy subjects during TDD but not during skin pull stimulation per se. Thus, it seems reasonable to suggest that DLPFC is involved in tactile decision making based on proper tactile input ."Just think about that for a minute: tactile decision making - not just sensing.
Interestingly the authors state that they saw no activation of S1. It may be that S1 responds only to novel exteroception. Perhaps once the rod was glued in place, the S1 ignored it, and, perhaps Ruffini ending information bypasses S1, reaches the DLPFC through some other pathway connected to interoceptive processing, but only if dorsal column information is available in the first place to be sent there.