@Jonathan Edwards, I just saw your comment about the Edwards et al predictive coding model. Please allow me the honour of summarising it for you!
Predictive coding is all the rage at the moment in cognitive neuroscience, so these authors decided they would borrow from that literature to create a "scientific" account of functional movement disorders. It is one of the finest examples of neurobabble I've ever seen.
The model goes like this:
1. Predictive coding approaches view organisms not as passive processors of incoming info, but as active predictors of what is likely to happen next. Organisms are innately driven to make their predictions as precise as possible. We don't "like" to be wrong about out predictions, so when we get it wrong and we get a nasty surprise, we adjust our future predictions so that won't happen again. So if you're wearing heavy boots and you accidentally trip on the stairs (woops, predicted I'd make that step, didn't expect that, not nice!), you adjust that movement next time to avoid that happening.
2. People with FND have formed a powerful expectation that they cannot move some part of their body in a normal way. This expectation need not be a conscious belief, but it must be a powerful expectation. Maybe they really couldn't move it for a while (maybe they broke their leg?), who knows, anyway, they formed that expectation somehow.
3. Given that a mismatch between prediction and reality is an aversive state for the organism, we are powerfully driven to reduce nasty surprises. So if you very powerfully, strongly believe that your legs tremble, discovering they don't would be a great surprise indeed. To avoid the inherent aversiveness of such a surprise, the FND patient unconsciously adjusts their movement to fit their expectation.
4. Hey presto, there you have it! A movement disorder without any organic basis!
5. But wait! Right now, you're thinking, "But yea, people recover from movement problems all the time - like broken legs and stuff. So we're all capable of adjusting our expectations when reality not longer fits them. What's so different about FND?" Well, it's good you asked because the difference is that FND patients have formed an
abnormally strong and unshakeable belief that they have a permanent disability.
6. But wait! Now, you're thinking, "But why does the belief get this strong in the first place?" Answer: because FND patients have
a psychological dysfunction that makes their beliefs in their disorder unshakeable - they are overly anxious, overly depressed or overly focused on their own bodily sensations.
Hey, look what happened there - we did a full circle and came back right where we started - to a psychological explanation!
We also violated the very core of predictive coding models - they emphasise the evolutionary importance of aligning our predictions with reality, not the other way around!
Its priceless.
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