Sensory Motor Amnesia is a condition of persistent involuntary muscle activation. The muscles always maintain a constant level of tension without any input from the conscious mind. There are numeous tiny sensors in your muscles that continually feed back to the brain information about the length of the muscle, its position in space, how much resistance it feels, etc. These signals are usually integrated by your subconscious mind without you being aware of them. Your body adjusts spontaneously to maintain position for whatever activity you are doing.
In sensory motor amnesia the brain loses its connection with these sensors & “forgets” that it has control over those muscles.
The involved muscles become stiff and painful which leads to limitation of movement even though there is no diagnosable joint or nervous system problem. The perception of pain arises from the disconnect between the brain & body.
How does Sensory Motor Amnesia Develop?
If you do any action over & over again the body learns how to do that action with less conscious input.
When I sit slumped over a computer typing all day, it becomes easier & easier to assume that position. The brain sends messages to certain muscles to tighten up to maintain my posture. My body becomes more efficient at maintaining the slumped position & it becomes difficult to assume any other. The muscles involved have received the “tighten up” signal so often that they now do it even when the signal is not present. It has become a habit and any office worker knows the discomfort that can result.
It’s similar to learning to ride a bike. At first you need to pay attention to every detail but after a while you can just ride effortlessly. Your body “just does it” so your brain can pay attention to traffic etc.
Another time when sensory motor amnesia may develop is after an injury. If we have been injured then we adopt new behaviours to protect the injured area, limping is one example. It changes the way we walk to avoid the pain of using an injured ankle. If the injury is slow to heal, though, we may absorb these protective behaviours into our “normal” way of moving.
This is sensory motor amnesia which in turn leads to the development of muscle imbalance and increased risk of injury. Research has shown that people who have had an ankle injury are more likely to fall again on the same ankle but that balance exercises can reduce this risk. Improving the brains ability to sense the position of the foot reduces the risk of further falls.
What are the symptoms?
Tight painful muscles are the main symptom of sensory motor amnesia.
The muscles may cease to respond to messages from the brain, so that the sufferer is unable to relax the involved muscles. Since the muscles involved to not relax and lengthen normally when the opposing muscle is used there is typically limitation of the range of motion.
To give an example, if you stand with your arms by your sides and curl your hand up toward your shoulder, the bicep muscle on the front of your arm must contract and shorten. At the same time the tricep muscle on the back of your arm must relax and lengthen.
The constant contraction maintained in the affected muscles causes them to become weak which contributes to clumsiness & distorted movement patterns. Which make recurrent injury more likely.
What treatments work?
Because sensory motor amnesia is not caused by a structural problem, it is possible to reverse the condition without surgery or invasive medical procedures. The “habit” of stiffness & pain can be unlearned. Because the condition is being maintained by the lack of connection between the brain & the muscles, it is possible to reverse it if you can regain that connection. There are many ways to do this such as yoga, tai chi & even some mindfullness practices, but the most effective technique I have come across is pandiculation as taught by Thomas Hanna in Somatics. This involves a conscoius contaction followed by a slow relaxation.
The aim is to consciously produce the behaviour that is being maintained unconsciously then then allow it to relax.
In treatment of my own problems, I have found this to be extremely effective. My pain is usually in muscles opposite to the ones which need to be contracted to provide relief.