Wednesday, October 19, 2005

Neuromatrix 7: Action Neuromatrix

The Action Neuromatrix: notes from p. 16, Topical Issues in Pain, Volume 3:

The output of the body neuromatrix directed at two systems;
1. the neuromatrix that produces awareness of the output and
2. a neuromatrix involved in overt action patterns. is important to keep in mind that, just as there is a steady stream of awareness there is also a steady output of behavior (including movements during sleep).

Apart from a few reflexes (such as withdrawal of a limb, eye-blink, and so on), behaviour occurs only after inputs have been analysed and synthesised sufficiently to produce meaningful experience. ...When we respond to pain, (by withdrawal or even by phoning for an ambulance), we respond to an experience that has sensory qualities, affect, and meaning as a dangerous (or potentially dangerous) event to the body.

I propose that after inputs from the body undergo transformation in the body-neuromatrix, the appropriate action patterns are activated concurrently (or nearly so) with the neuromatrix for experience. Thus, in the action-neuromatrix, cyclical processing and synthesis produces activation of several possible patterns and their successive elimination until one particular pattern emerges as the most appropriate for the circumstances at the moment. In this way, input and output are synthesized simultaneously, in parallel, not in series. This permits a smooth, continuous stream of action patterns.

The command, which originates in the brain, to perform a pattern such as running activates the neuromodule, which then produces firing in sequences of neurons that send precise messages through ventral horn neuron pools to appropriate sets of muscles. At the same time the output patterns from the body-neuromatrix that engage the neuromodules for particular actions are also projected to the sentient neural hub and produce experience.

In this way, the brain commands may produce the experience and movement of phantom limbs even though there are no limbs to move and no propriocptive feedback. Indeed, reports by paraplegics of terrible fatigue as a result of persistant bicycling movements (like the painful fatigue in a tightly clenched phantom fist in arm amputees) indicate that feelings of effort and fatigue are produced by the signature of a neuromodule rather than any particular input patterns from muscles and joints.

Why is there so much pain in phantom limbs? I believe that the active body-neuromatrix, in the absence of modulating inputs from the limbs or body, produces a neurosignature pattern, including the high-frequency bursting pattern that typically follows deafferentation, which is transduced in the sentient neural hub into a hot or burning quality. The cramping pain, however, may be due to messages from the action-neuromodule to move muscles in order to produce movement. In the absence of the limbs, the messages to move the muscles become more frequent and ‘stronger’ in the attempt to move the limb. The end result of the output message may be felt as a cramping muscle pain. Shooting pains may have a similar origin, in which action-neuromodules attempt to move the body and send out abnormal patterns that are felt as shooting pain. The origins of these pains then, lie in the brain.

Surgical removal of the somatosensory aeas of the cortex or thalamus fails to relieve phantom limb pain...the new theory conceives of a neuromatrix that extends throughout selective areas of the whole brain. Thus to destroy the neuromatrix for the body-self, which generates the neurosignature pattern for pain, is impossible.

(There follows rather long discussion of data collected that involved injections of anathesthetics into various parts of the brain and the results in rats, the gathering of direct evidence that the brain, neuromatrix can generate sensation on its own)...

The existance of phantoms in people born without a limb or who have lost a limb at an early age suggests that the neural networks for perceiving the body and its parts are built into the brain. The absence of inputs does not stop the networks from generating messages through out life.

In short, phantom limbs are a mystery only if we assume the body sends sensory messages to a passively receiving brain. Phantoms become comprehensible once we recognize that the brain generates the experience of the body. Sensory inputs merely modulate that experience; they do not directly cause it.


I think the implications for us as professional treaters of people are huge. We aren’t working with human bodies, we are working with human brains, every time. We are “inputting” a novel “neuromodule” which can produce a “subsignature” which can inform and alter the neurosignature of the neuromatrix. With our presence, voice, contact both psychological and physical, we use our capacity to reflect back (at least to intact nervous systems) the changes that they are making under our hands. We are literally joining nervous systems with our patients for a time.

It seems to me that this provides huge new multi-dimensional space in which to grow as professionals. Formal PT organizations should work to consolidate, reflect and support this new growth space, especially now that they can remain congruent with emergent science based thinking such as this updated pain model.

Physiotherapists/physical therapists can work with a new awareness of being 'neuromodulators', not just mobilizers or manipulators (a very Cartesian idea) or exercise suggestors/enforcers. With this new awareness, we can assist each individual to find the movement that is somewhere inside them, that needs to be expressed for the neuromatrix to reestablish correct function ( i.e., the "consummatory act" alluded to by Patrick Wall, Melzack's fellow pain researcher). Each patient can be helped to become his or her own neuromodulatory specialist, able to influence their own neuromatrix anytime they like, by enacting "neuromodulatory action."

Hands-on techniques help a neurosignature change its action output.

Let's put an end to all our perceptual fantasies we entertain about how we think we are affecting "tissue"; let's use instead this new set of concepts, this new theory that explains and universally translates all the carefully preserved and passed on traditional means by which people have always 'laid hands' on each other. Let's keep hands-on techniques and dissect away all incomplete and misleading explanations.

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