Wednesday, October 17, 2018

Sensing Your Reality

Courtesy of Dr Matthew Long.
As chiropractors we are fascinated by the intricacies of spinal manipulation, and even more intrigued by what it might do to the nervous systems of our patients (particularly the brain). In the last few Clinical Clarity Blog articles we have looked at the evolving brain-based models of spinal derangement, and discussed new ideas about how and why such problems might develop in the first place. Increasingly, it seems that those with spinal disorders have a distorted sense of 'self' - a misperception of their spinal tissues that has been described as a disruption of their 'body schema' or 'cortical body matrix'. This is a far more profound idea than a simple proprioceptive deficit, and impacts upon other important areas of the brain such as the limbic system, and the autonomic nervous system.
In essence, the human nervous system requires vast amounts of sensory data to orchestrate its responses to our ever-changing environment. The more accurate and timely the data, the more likely that we can respond in an appropriate fashion. Furthermore, our great capacity to learn means that over time our brain will enhance this data with its own predictions about what future inputs it is going to receive, in the hope of improving response times and survival. But in order to make informed predictions, our brains need data. Lots of it. Unfortunately, those who live a modern, and relatively sedentary, lifestyle are starved of the rich data supply necessary to allow their brains to function as nature intended. Without sufficient data they cannot construct an accurate three dimensional model of their world - both external and internal.

This brings me to the main subject of this Blog article - TED talk by cognitive neuroscientist Professor Anil Seth entitled"Your brain 'hallucinates' your conscious reality". As Professor Seth says,
"Imagine being a brain. You're locked inside a bony skull, trying to figure what's out there in the world. There's no lights inside the skull. There's no sound either. All you've got to go on is streams of electrical impulses which are only indirectly related to things in the world, whatever they may be. So perception - figuring out what's there - has to be a process of informed guesswork in which the brain combines these sensory signals with its prior expectations or beliefs about the way the world is to form its best guess of what caused those signals. The brain doesn't hear sound or see light. What we perceive is its best guess of what's out there in the world."
To quote Professor Seth again,
"Instead of perception depending largely on signals coming into the brain from the outside world, it depends as much, if not more, on perceptual predictions flowing in the opposite direction."
This is an important idea that is worth pondering for a moment. Our sensory perceptions are largely dependent upon internal models that we have developed over time, and we use these to predict our world. But we can only predict what we have experienced, and we can only build models based upon data that we have accumulated. If we all still lived the 'hunter-gatherer' existence that nature intended, then we would have developed a vast repertoire of movements and motor patterns necessary to survive in such a variable environment. But most of us subsist with a limited array of stereotypical movements (walk, sit, stand, sit, text, type, sit, text, etc), with the odd gym session thrown in. This is not the same as a life that is lived in variable motion. As such, our brain struggles if we suddenly ask it to perform a movement for which it has limited data to work with, such as cleaning out a cupboard under the stairs, or reaching up at an awkward angle. These are the stories that our patients tell us every day, usually preceded by the words, "But I didn't do anything". Without data we cannot make accurate predictions and our ability to control our body is compromised. When we move, we make mistakes - internal mistakes - and this can lead to tissue injury and pain. 

So what has all of this got to do with chiropractic? 

Spinal manipulation should be seen as a method of enhancing input to the nervous system. Adjustments may help our patients by delivering highly leveraged proprioceptive stimulation to areas of the sensory neuraxis that have become depleted and deconditioned through disuse and injury. Hopefully then, with more data flowing in, the brain can make better predictive models that allow us to navigate our world more safely and accurately.
Something to think about...

Dr Matthew D. Long
BSc (Syd), M.Chiro (Macq)