Models of Pain and Movement

There are various models used to understand pain: the neuromatrix model, the biopsychosocial model; Louis Gifford's Mature Organism Model; the Onion skin model, the biomedical model. And for motor learning and physical training there is the constraints based model, or dynamic system theory, the various Russian sports science models, non-linear pedagogy, etc.

I often see debate as to the relative merit of these models, which is a good thing. But what I think is not such a good thing is when people argue that because a model has a certain flaw or limitation, it is fatally deficient. Or that using this model will always lead to error. Or that existing problems with current models requires a complete and radical revolution in our thinking. These arguments are particularly common in regard to models about the brain because, let's face it, the brain is pretty hard to model. 

The way I look at it, all models are necessarily wrong, at least to some extent. But some models are still useful. We need to be aware of how a particular model might lead us astray, but we also need to appreciate how it can provide insight.   

Building models is a fundamental part of trying to understand the world in any systematic or organized way. The world has too many details and complexities to be taken in all at once. In order to really understand a particular phenomenon, we need to focus on certain essential details while ignoring others.

For example, to understand the movement of large objects in response to forces, we focus on the mass and velocity of the object, and the magnitude and direction of the forces applied to it. But we ignore non-essential but very real details like the color of the object, the shape of the object, or even the effects of friction. The result is a model with simple equations like force equals mass times acceleration. 

We can test the accuracy of the model by seeing whether it makes accurate predictions. If it does, or leads to better understanding and control over the events we are trying to explain, it is a success. Further progress can be made by noting the limitations of the model, arguing about whether other models are better, making improvements to existing models and so forth.

Although we can improve the accuracy and utility of models, they can never be complete or accurate representations of the world. In order to fully model the world, we would have to build another world! That’s impossible, and it wouldn’t really help anyway. So models are not mirrors of reality, but simplified reflections. They are therefore, to at least some extent, "wrong." But again, they can be incredibly useful.

Newtonian mechanics allows us to make amazingly accurate predictions about the movement of large objects like planets. But it fails to describe events accurately when objects are very small, or moving near the speed of light. Under these circumstances, we need different models - the theory of general relativity or quantum mechanics. So Newton’s “laws” are not universal, but they remain accurate in the “middle sized” world that is our usual area of concern. 

Here’s a relevant quote from Sean Carroll (a very smart physicist) in his new book The Big Picture:

Our best approach to describing the universe is not a single, unified story but an interconnected series of models appropriate at different levels. Each model has a domain in which it is applicable, and the ideas that appear as essential parts of each story have every right to be thought of as “real.” Our task is to assemble an interlocking set of descriptions, based on some fundamental ideas, that fit together to form a stable planet of belief.
. . .
Our fundamental ontology, the best way we have of talking about the world at the deepest level, is extremely sparse. But many concepts that are part of non-fundamental ways we have of talking about the world — useful ideas describing higher-level, macroscopic reality — deserve to be called “real.”
The key word there is “useful.” There are certainly non-useful ways of talking about the world. In scientific contexts, we refer to such non-useful ways as “wrong” or “false.” . . . Every scientific theory is a way of talking about the world. The world is what exists and what happens, but we gain enormous insight by talking about it — telling its story — in different ways.

I agree!

The human body is one of the most complex organizations of matter in the known universe. To understand it, we must build models, use metaphors, and deal in abstractions. This necessarily involves ignoring certain details, creating simplified pictures, and relying on metaphors that have the potential to mislead. But we have no choice! Models and metaphors are indispensable thinking tools to understanding the body. Is the brain a computer? The heart a pump? The kidney a filter? The nerves telephone wires? In some ways yes, and others no.

Each model is a different perspective from which to see the world, with its own unique insights and blindspots. For example, you can look at movement or pain from the perspective of the musculoskeletal system, the nervous system, the metabolic system, the immune system, or the endocrine system. You can take a microscopic view to consider the behavior of individual cells, or zoom out for a big picture of the relationship between larger systems. Some perspectives might be highly informative for a wide variety of purposes, and generally foster an accurate perception of the viewed object. These perspectives are great. Others may get you looking in completely the wrong direction. These perspectives suck. But there is no one perspective that can offer complete understanding of a multi-dimensional phenomenon like pain, movement, or any other event in the human body.