Tactile Chicken Soup for the Brain: 2-pt discrimination | Modern Manual Therapy Blog

Tactile Chicken Soup for the Brain: 2-pt discrimination


This guy has nothing to do with that statement, but looks like someone who might say that...

Today’s blog will discuss some interesting research on cortico-somatosensory reorganization, and its implication to pain patients and the art of physical therapy as a whole.

One factor that can feel unsettling is summarizing or justifying treatment with a much more complex explanation of mechanism, in part due to patient education, though as practitioners we just have to accept that humans are complex and continue to strive to find meaningful variables, explanations, and interactions that promote proper beliefs on behalf of the patient regarding their condition.

The Practitioner may want do delve into a deep understanding of treatment interaction, mechanism of effect to interface (tissue being “treated”), application of treatment and education, all for the purpose of building a proper framework. From patient perspective however, I believe simple is better: we can choose to communicate concepts of the body recovering to its normal state (ie getting rid of pain or restoring function) to patients in a way that borders the conversation between two laboratory physiologists students prepping for an exam, to explanations that are tangible to the patient (though may seem trite).

This can be a particular area of struggle for myself when internalizing the way a patient presents, then externalizing it verbally in terms of approach to explanation of symptoms, treatment, patient buy-in, adding a bio component that is meaningful as well as psychosocial component that is tangible and meaningful. Beyond that, there can be many other intended influences passed upon the patient that don’t necessarily warrant an explanation (maximize placebo effect while setting realistic expectations and practice good listening and empathy skills with explanations that don’t dismiss or belittle patient concerns).

We do this all the time, decide what to verbalize and what not to; some of it is subconscious. We don’t start an evaluation by saying“research shows that good eye contact and listening when talking to people in pain during their initial sessions is predicative of a good outcome” then sit watching the patient and nod… but with all the information on a persons response to treatment elucidated by placebo studies, psychosocial studies, and pain science in general we have a lot to choose from in terms of what to and what not to verbalize.

Which brings me to the topic of a smudged homunculus…

I like to reference the studies by Moseley, as well as Louw, that discusses 2-point discrimination deficit in CLBP patients, when I find a reasonable time to do so with patients.

I think a meaningful way of getting some rather interesting and hopeful research across to a patient in pain may be something like this:

When were experiencing pain, we start to move and act differently than before. Initially this may be proper and important, as we want to protect the possible tissue injury, though if our body continues to react, move, and live as if injured it can become habituated. We all have an internal map of our bodies in our brain, and research shows that people with persistent pain start to recognize the part of the map representing the painful body part less. This results in improper interpretation of information getting to the brain, and affects what you feel as pain and how you move that area.

A recent research study looked at sensation awareness in lower back pain patients, and they found that the people in pain had difficulty discerning how many pins were poking them, where they were and how far apart they were. The also found that they could train this over a few months, and the people had a significant reduction in pain once as they became better at noting the accuracy of the pin prick.

Most interestingly, the people only improved if they were asked to scrutinize the sensations and report what they were feeling (placing pins into the back and creating a stimulus without having the patient consciously focus on what and how they were feeling it had no benefit).

Although verbose, choosing to convey this info to the patient may be relevant for a few reasons:

  • It validates that in persistent pain patients something could be “wrong” or “amiss” for the patient, without describing damaged joints or tissues
  • It demonstrates that changes can be made, and points the periscope at the tip of the iceberg that there is more to getting better than “fixing the joint with a technique”
  • It shows the possible importance of awareness to the patient, that some portion of them improving will be pending on them making their exercises (or manual therapy) meaningful and not just “something done to their body”
  • It opens up a window for more questions from the patient, if THEY want to learn more about it! (spouting intricacies of pain being an output may inhibit relations if poorly administered)
So back to practitioner framework, why is the research of impaired 2-point discrimination important? We know that somatosensory organization of the brain changes (maladaptive) when there is dysfunction (this is seen in not only pain, but post stroke). Loss of limb leads to invasion on the severed limb’s representation by surrounding area representations. It abides by the “use it or loose it” principle. That’s right, neuroplasticity can be for better or worse. Further, when we acquire a skill, these (adaptive) changes are reason for our performance and retention of that skill (why a professional violinist may have a differently organized map of the fingers). In the Motor cortex, neural density and cortical matter is correlated with the importance and use of that area! It can be “sharpened” and adapt by training, just like it can be “dulled” by non-use and habituated pain behavior.

The Motor cortex gets info/inputs from the somatosensory cortex and digests it in order to coordinate an output of motor control. Thus disturbances in output (how we move) are related to altered input from the somatosensory cortex. Though alleviating pain doesn’t necessarily mean the output of motor function, fluidity of movement, and movement options restore automatically. This is why functional movement based exercise is important, and in particular, perhaps awareness to movement. And the “functional” (although this term can be annoying) is important in that in order to be a catalyst towards a cortical reorganization change, it needs to be meaningful to the patient.

*as a side note, what annoys me with “everything must be functional” is that there needs to be a starting point with every patient; if their current function is maladaptive then replicating a functional exercise component may be difficult. Giving some form of input (maybe its an isometric, maybe just some simple pelvic rocking) may be a good starting point to build upon the awareness and ability, while educating the start slow and build concepts of graded exposure.

Although I know little of “Feldenkrais” physical therapy, I imagine part mechanisms of their success is due to this remapping that takes place, as they are “feeding” the brain with lots of slow and thoughtful inputs through movement. I still think an explanation is warranted on why the person should pay attention to the movement, as if not, the person is just knowing that “every 2 hours I need to do a pelvic clock, that’s supposed to make me better”…

I like how Tim Flynn and Emilio Puentedura discuss manual therapy in a recent publication discussing manual therapy and some of the paradigm shifts concerning “mechanism of treatment” (just because it “works” doesn't mean that the specific treatment was the “fix”)
  • “There is very little evidence that manual therapy performed under anesthesia is effective for CLBP and perhaps this is because we need to “manipulate”the brain, and not just the joints and other peripheral tissues, to bring about a change in the pain experience”…
  • Current evidence suggests that these representational body maps are dynamically maintained in the brain (neuroplasticity) and are negatively influenced by neglect, decreased movement, and pain
  • They touch on that part of skilled MT is certainly feeding inputs, as in “do you feel this part of your spinous process here, whats it feel like with this motion? Is this painful? Can you feel a slight stretch here?
These “techniques” can certainly be beneficial, but were continuing to consider lots of different reasons for their efficacy. Physical therapists like Jason Silvernail have been talking about this for many years, in what he at one point titled “crossing the chasm” when speaking of some of the reconceptualization for what our treatment is doing. Finding ways to communicate these concepts isn’t always easy (with both patients and fellow PTs), but if you’re at all a curious PT its impossible to ignore.

Although the aforementioned study discusses sensory input via pin prick, the body is experiencing sensory input via movement all the time. The take home to me is that under the influence of altered inputs feeding a cycle of altered outputs, we are more hopeful of changing this if we add awareness and discrimination to our inputs: be it exercise our MT. Visual feedback may be one way being able to constantly re-scrutinize positional awareness, test and train. In this sense, we’re giving more information, which may change processing in hopes to achieve an overall more adaptive system.

-Tal Blair, DPT


Moseley et al. Tactile discrimination, but not tactile stimulation alone, reduces chronic limb pain. Pain 137 (2008) 600–608

Catley et al. Is Tactile Acuity Altered in People With Chronic Pain? A Systematic Review and Meta-analysis. The Journal of Pain, Vol 15, No 10 (October), 2014: pp 985-1000

Louw A, Farrell K, Wettach L, Uhl J, Majkowski K, Wedling M 2015 Immediate effects of sensory discrimination for chronic low back pain: A case series. New Zealand Journal of Physiotherapy 43(2): 58–63.

Flynn et al. Combining manual therapy with pain neuroscience education in the treatment of chronic low back pain: A narrative review. Physiotherapy Theory and Practice · June 2016

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