Touch is an immensely important sensation and has been linked to many healing properties, so too has proprioception (the sense of body position in space). If you will, allow me to try to link these senses to pain and the body’s self representation.
So touch and movement helps with pain perception? How does all that happen?
First, you get sensory stimulus in. Afferent signals. (How do those sensors function? What do they look like? See external link here.) This information goes to your sensory homunculus where you have THE representation of your own body and self stored. (Brodmann’s area 3a-b, 2,1 the post-central gyrus)
Photo credit: http://www.merckmanuals.com/media/professional/figures/NEU_homunculus.gif
Each area of your entire body is represented here. The size of the area is directly related to the density of sensory fibers in an area. The densest areas include the hand, fingers, mouth and tongue, etc. You feel yourself and know who you are because of their input. When these nerves interact with the environment (wind blows on your skin, you squeeze into skinny jeans, etc) then you get representational information about the outline, borders and position of your body.
( Side note: notice how little kid’s first drawings of people often look like the homunculus man? Is that because they are drawing what they perceive to be important: the parts most represented in their own body perception? )
The skin is stimulated by heat and touch, etc. The more you are touched in an area the better defined that area becomes in your brain, in your sensory cortex, in your mind, in your SELF. It may not actually grow in size and the density of peripheral fibers does not increase but the accuracy and confidence with which that area is known will increase.
The same can be said for proprioception. The more information your brain-self-somatosentory cortex gets about you, the better you are represented. This comes from Golgi Tendon Organs, muscle spindles, joint mechanoreceptors, etc. These guys are activated with movement and stretch and muscle contraction and load bearing and jumping and all the wonderful physical things that we are able to do. This gives the brain stimulus as to how the body is actually moving and oriented. The brain likes to know what is going on, so it can decide that that area is doing fine.
I believe the connection is as follows.
Low sensory input from a body part can lead to a dysfunctional or unhealthy body representation. This, in turn, may cause a pain output. (and/or vice versa?!)
Amputees often suffer from phantom limb sensations or even pain. These are feelings in a limb that no longer exists on the person… but still does exist in the brain. The sensory homunculus wants to verify that body part. That’s a fancy way of saying the neurons in that area fire and are seeking to work, seeking to do something with their time, if you will. They are met with….. silence. There is no longer a limb there to send a “don’t worry, I’m OK, s’all good” signal. So, since we know pain is an output of the brain, that output goes unchecked by the lack of actual information and the individual may feel sensations of the limb being contorted, or stuck in the last known position before amputation, or just simply feel pain. Amputees often get relief with wearing their prosthesis because it gives them a sensory cue to the area. See here from the BBC.
We also know that the sensory homunculus will change via neuroplasticity to the afferent signal sent in. This study: shows that when/if a finger is cut off, it was demonstrated that the adjacent areas of the brain will converge and take over that brain real estate that once represented that finger. The neurons in that area don’t like to be idle, so they pick up doing the job of their neighbors. So in effect, the area that once housed your finger is now smaller, or non existent. It is also described here in a study on amputees.
The same goes with chronic pain. That painful area of the body is not well represented in the brain, it may be smaller or changed in some way. This is seen in MRIs of Chronic Regional Pain Syndrome (CRPS) or Chronic Low Back Pain (CLBP)patients.
Here is a wonderful post from bodyinmind.org about touch speed on body perception.
Lets say you hurt your arm. You often get nociception and resultant pain. You also immobilize the limb and dont move it for fear of pain or to protect it to allow for healing. This deminishes the healthy input to your body-self. Now your body only recieves negative stimuli about the area. Now, either because of a protective mechanism (unkown?) or as a neuroplastic lack of sensory/proprioceptive input, that area shrinks. The brain stops feeling an ‘arm’ and simply feels nociception. Not a good trade-off. Here is a great post from Bodyinmind.org on a study about how touch sensation is sent around that awesome cortex of ours.
We know this anecdotally when we hurt ourselves. If we cut our arm, for example, that spot will hurt. We can also touch the area around that cut and we hurt. We feel the pain, not the touch sensation that we should. Now, of course, touch can stimulate the A-betas and reach the spinal cord quicker than the Delta and C fibers. But this does not often work in the direct area of the injury and is more likely to occur just outside the area but still dermatomally. So, in the area that we feel touch and can utilize the gate-control theory, that area of the body will stay represented fully. The body area sending nociceptive input, however, may run the risk of distorting the homunculus.
In studies individuals with CLBP or other chronic pain were asked to draw their painful body part as part of drawing their whole body. Often this area was distorted (controlling for drawing talent) or left blank on the paper. (self image: insert “it hurts here” picture with no body part). Here is Lorimer Moseley’s paper on the whole thing.
Can you see the connection now? Touch and movement give the brain something to do, something to wrap it’s ‘mind’ around, something to focus on. This lends more credibility to exercise as a way of giving proper and healthy input in. Those who do yoga, for example, get an amazing amount of information about their body, same goes with sports players and active people of all types. Think how tuned in a painter’s brain is to their arm, wrist and fingers as compared to a CRPS patient. Think about how big the area in charge of the foot and leg is for someone born with no arms and who has learned to play drums with his lower extremities. Do you think it’s the same as you and me? This difference is probably amazing.
So, as a practitioner: make your patient move. Active movement is self limiting as it concerns pain. most people will stop short of hurting themselves and with the right coaching they can learn to move more and more without kinesiophobia (fear of movement).
Click here for a nice short video post from NOIjam… move, all day!
Also think about how your manual skills come into play. Massage and therapeutic touch could literally reorganize the individuals somatosensory cortex and homunculus. It’s all about that input.
Check out some research! Dunigan B, Teresa K, Morse B. A preliminary examination of the effect of massage on state body image.Body Image.Elsevier Press. 2011:8(4);411-414.
Get to know yourself and spread the word: Touch and move. All day.
– Matt D