TACTILE DIRECTION DISCRIMINATION IN THE DORSOLATERAL PREFRONTAL CORTEX

My take on why manual therapy "works", part 5.

OLDER POSTS IN THIS SERIES

Part 1: IS MANUAL THERAPY EVEN NECESSARY? 

Part 2: NEUROTAGS! YOU'RE IT! 

Part 3: ABOUT "LEARNING" 

Part 4: SKIN STRETCHING AND MOVEMENT ILLUSIONS

NEWER POSTS IN THIS SERIES

Part 6: MORE ABOUT DORSOLATERAL PREFRONTAL CORTEX 

Part 7: TREATMENT CONTEXT, NON-SPECIFIC EFFECTS 

Part 8: SOME FINAL THOUGHTS ON NON-SPECIFIC EFFECTS

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The next statement in the SomaSimple post is:

"This will engage the dorsolateral prefrontal cortex, even. (See Lundblad et al 2010, about Ruffinis and DLPFC)"

It's time to revisit that Lundblad paper (1). Actually, Olausson was involved in it, of course..
He seems to be involved in all papers that involve exteroceptive or interoceptive skinput.

Here is the full reference:

Lundblad LC, Olausson HW, Malmeström C, Wasling HB. Processing in prefrontal cortex underlies tactile direction discrimination: An fMRI study of a patient with a traumatic spinal cord lesion. Neurosci Lett. 2010 Oct 15;483(3):197-200

ABSTRACTWe 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.

The implications are kinda huge, actually... Here is my confirmation bias, full on, full blast:  I very much like the idea that Ruffinis (my very favourite sensory ending, way out in skin, easy to manipulate - dead easy) are somehow totally tied up with tactile direction discrimination! Not just sensing, but direction discrimination! Movement illusion!
This study demonstrated, in a single subject with an incredibly rare iatrogenic spinal cord lesion (that only affected his dorsal column pathway(3), and only on one side!..the control group was built right in!!).. that the dorsolateral prefrontal cortex activated on the appropriate (opposite) side, with skin stretch, inside an MRI machine, from skin stretch on the unaffected leg, but did not with skin stretch on the affected leg, whereas everything else in the brain activated bilaterally. Effectively isolating DLPFC as being divorced/severed from input from (specifically, one presumes) Ruffini input. By said lesion to the dorsal column pathway.

I mean, how often does an opportunity to combine all those factors into one study come along? The odds against this combination of factors plus a researcher canny enough to want to know, and willing to build a machine that would be acceptable to a scanner, plus a patient willing to go in one just for the research, after having his spinal cord injured by an epidural injection gone wrong in the first place for something totally unrelated - I mean.. sometimes the universe knocks me back on my butt, it's so marvelous at coughing up stuff like this every so often!  
It's pretty unlikely that something like this would ever be replicable. But that doesn't mean it isn't great science and great scientific deciphering.

OK, enough of the science appreciation. Please read the blogpost I linked to, where you'll see a picture of the device that the patient wore inside the scanner, and a description of the paper itself. And a lot more gee-whiz golly-gee science appreciation writing by me that you may ignore if you so choose.

1.  Lundblad LC, Olausson HW, Malmeström C, Wasling HB. Processing in prefrontal cortex underlies tactile direction discrimination: An fMRI study of a patient with a traumatic spinal cord lesion. Neurosci Lett. 2010 Oct 15;483(3):197-200

2. Dermoneuromodulation: Ruffini sensory endings and dorsolateral prefrontal cortex HumanAntiGravitySuit, Mar7/2012

3. Overview of ascending pathways: Dermoneuromodulation: Ascending pathways Mar11/2012