Pain and the Brain – the mind/body connection
Mind/body interaction and our perception of pain has been studied intensively in recent decades. We have discussed pain mechanisms previously on this blog but suffice it to say at this point that the concept of the pain experience being simply related to activation of nociceptors, as a consequence of tissue trauma, is now widely recognised as only one potential mechanism in the perception of pain. The IASP (international association for the study of pain) has defined pain as an ‘unpleasant sensory and emotional experience associated with actual or potential tissue damage’. Now that covers a fair spectrum of sensations!
It has now become routine in physiotherapy practice to consider that, non-resolving / slowly resolving conditions, are attributable to central nervous system malfunction (sensitisation) and those which behave predictably fit neatly into the categorisation of nociceptive pain, attributable to local tissue trauma. Here the resolution of symptoms is associated with the reduction in local inflammatory signs such as, swelling, sensitivity, tissue thickening and load tolerance.
The mechanism of sensitivity reduction is attributed to the resolution of the so called ‘inflammatory soup’, which perpetuates peripheral sensitisation and resolves in accordance with known tissue healing times.
The biological reality is that nociceptive stimulation has immediate central nervous system manifestations in terms of neuronal activation at the spinal cord level and regions of the mid brain (thalamus) and sensory cortex. Much of the research looking at central mechanisms of processing, have evolved from Ronald Melzack’s concept of the neuromatrix, which postulated a neural signature within the brain associated with an individual’s response to painful stimuli. Much of this work has been expanded upon by physiotherapy’s own Lorimer Moseley , Herta Flor and other brain imaging specialists.
We know from much of the work on chronicity and disability perpetuating factors in low back pain, that there are multiple environmental and attitudal factors (classified under the flags system and here which also profoundly influence the level of symptoms and disability experienced. The vast majority of research in this area seems to relate to persistent low back pain and whiplash. If we were to consider many of the other musculoskeletal conditions with a high propensity to chronicity i.e. tennis elbow, plantar fasciitis, Achilles tendonitis and headaches the questions is whether these neuronal factors are the key determinates in perpetuating sensitivity, or whether we are still looking at a peripheral nociceptive mechanism?
Much of the interesting work by Moseley’s team involves illusionary stimuli to alter neuronal output or influence symptom experience. This can involve manipulating perceived sensory input or altering the perception of motor output. One interesting illusion, which illustrates mind/body interaction and its manipulation is the ‘thermal grill illusion’.
The Thermal Grill Illusion
Todd Hargrove has written eloquently on this and I have extracted some of his thoughts below.
The thermal grill illusion is a phenomenon of sensory motor mismatch. The thermal grill illusion is created by placing the index and ring fingers in warm water and the middle finger in cold water. This unusual sensory input apparently confuses the brain into thinking the middle finger is in boiling water because it somehow results in a feeling that the middle finger is painfully hot. In a recent study researchers induced pain through the thermal grill illusion and asked the subjects to press their fingers together. This cut the pain intensity by 64%.
However, they were unable to reduce the pain by doing several other forms of touching, such as touching the hands of the other people or by pressing their hands together in an overlapping fashion. The researchers noted that the thermal grill illusion was reduced only when thermosensory and tactile information from all three fingers was fully integrated. That is, the thermal illusion reduction required a highly coherent somatosensory pattern, including coherence between tactile and thermal patterns and coherence of stimuli between the two hands. In other words, the pain didn’t go away until the brain received sufficient sensory information to correct the distortions in the body maps.
One of the debates regarding nociception is the debate between perceived and actual tissue damage and the mechanisms of excitation of nociceptors . Whilst changes in sensory and motor firing patterns have been well documented in the presence of peripheral sensitisation (associated with tissue trauma), there appear to be other mechanisms of nociceptor sensitisation not directly associated with such evident trauma.
We know there are sub groups of nociceptors , which are chemo-sensitive, thermo- sensitive as well as the obvious mechanosensitive. Perhaps there are other sub classes of nociceptors, which perpetuate unpleasant sensory bombardment of the central nervous system. Although we have undoubtedly come a long way in our classification of pain mechanisms, there is a danger that the peripheral central mechanism pendulum has swung so far towards central mechanisms, that peripheral are being neglected.
How do you think the integration of pain mechanisms has influenced your clinical practice?
Do you use strategies that target the central nervous system to improve patient’s function?
Is anyone using illusionary techniques to treat musculoskeletal pain in their clinical practice?
Let us know your thoughts.
Enjoy the clinical challenge.
David.GHTime Code(s): nc