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Functional neurological disorder: new subtypes and shared mechanisms, 2022, Hallett, Dworetzky, Stone et al

Discussion in 'Psychosomatic research - ME/CFS and Long Covid' started by Andy, Apr 15, 2022.

  1. Ravn

    Ravn Senior Member (Voting Rights)

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    Slightly OT but stumbled across this alternative take on "PEM" while looking to update my understanding of predictive coding/processing. My understanding remains vague but I can see how a superficial reading of selected parts of the model could be misused to lend support to all manner of mind-body mischief.

    Anyway, "PEM":
    https://predictive-mind.net/papers/vanilla-pp-for-philosophers-a-primer-on-predictive-processing

    A slightly shorter and less dense - if overenthusiastic - explanation of predictive coding/processing if anyone's interested:
    https://www.mindcoolness.com/blog/bayesian-brain-predictive-processing/
     
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  2. Snow Leopard

    Snow Leopard Senior Member (Voting Rights)

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    I suggest this is because they are collaborating with younger scientists who are conducting those neuroimaging studies and may have slightly different opinions.

    @dave30th

    More to the point, they're merely speculating that there is a predictive system of sense inputs other than proprioception, without any empirical evidence, despite a century of research trying to look for such evidence.

    The brain doesn't need to predict fatigue or pain because a small amount of latency in those signals doesn't matter at all. Instead of a predictive coding system, we have a reflex system.

    There is a predictive coding system for proprioception, because our nerves are too slow to provide feedback in real time to provide precise motor control. (this research dates back to Helmholtz in the mid 19th century https://en.wikipedia.org/wiki/Predictive_coding)

    Their system is backwards because instead of relying more on sensory input to correct the model when it is incorrect, they are instead suggesting that the system decides to ignore sensory input and just mark one's own homework as 100% correct. This would necessarily lead to a loss in precise motor control (and hence does not apply to ME/CFS patients). They are also assuming that the brain doesn't have multiple sensory pathways to correct for when muscle (force/velocity) afferent signals may be incorrect - starting with the signals from the surrounding muscles, but also visual and touch feedback. If their model is correct, then all of these additional feedback mechanisms also have to be in error or are ignored by the brain.
     
    Last edited: Apr 17, 2022
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  3. Jonathan Edwards

    Jonathan Edwards Senior Member (Voting Rights)

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    That is a reasonable point but predictive coding applies much more widely than proprioception. It is relevant to colour and shade vision and to sounds, including speech perception. If the brain predicts that a square on a picture of a chessboard is in the shade of a vase then it will interpret it as white even though the shade of the image is the same as for black squares out of shadow.
     
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  4. Snow Leopard

    Snow Leopard Senior Member (Voting Rights)

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    I wouldn't strictly describe that as "predictive coding" though, as the reasons are more complex.
    Some of our perceptual processing related to hearing and sight are deliberately lossy (in terms of information processing) for example, in ways that aren't strictly related to accurate prediction of future sensory input. To put it another way, the brain filters the inputs to focus on what is deemed to be meaningful such as separating noise from speech, edge finding to provide spatial awareness and motion tracking which is needed for motor control of the eye, etc. The function is not to accurately predict the totality of the sensory input.

    This contrasts with the "perceptual coding" errors proposed by Stone et al. who flip the whole concept backwards and claim the higher level systems try to predict the noise rather than the meaningful signals and then lose the plot.
     
    Last edited: Apr 17, 2022
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  5. Jonathan Edwards

    Jonathan Edwards Senior Member (Voting Rights)

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    It is what the predictive coding people call predictive coding.


    I spend most of my time when not thinking about ME thinking about perception and writing articles on it. The predictive coding people are the main neurobiological theorists involved. They consider the brain to be a prediction machine with everything in perception derived from a 'Bayesian model', whatever that is supposed to be. Predictive coding is supposed to explain why we are conscious at all. It is blather, but it is the current fashion.

    There is a vast literature on illusions that fool the 'prediction machine' including colour and shape illusions, rubber hands and misinterpretations of lip movements and so on. There is masses of evidence for 'forward models' and 'efferent copies' and so on although as far as I am aware nobody can say how it actually works in individual neurons. My work is on how perception might operate at the individual neuron level. I do not doubt that comparisons and subtractions are widespread in all modalities but I don't think the neurobiologists realise quite what that needs to involve. Christof Koch and Idan Segev got somewhere near to it in giant locust visual neurons about twenty years ago but nothing much new seems to have materialised.

    So I don't think people like Mark Edwards are thinking in terms of proprioception particularly when they talk of predictive coding.
     
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  6. Snow Leopard

    Snow Leopard Senior Member (Voting Rights)

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    Why would they not think about the most strongly empirically demonstrated biological predictive coding systems? (I now realise this is a rhetorical question)
    That is where the language of 'forward models' and 'efferent copies' comes from (I'm a fan of Helmholz's work).

    The idea is that the brain (supplementary motor areas) has an effective model of the muscle efferents and specific afferents, such that when a motor signal is generated, an identical the 'efferent copy' is passed through, it provides a precise series of outputs that are then compared with the actual afferent outputs, which in turn revises the model. (of course there are other inputs too, vision, vestibular system etc)

    Knowing little about the field, and thinking about bottoms-up approaches, I'd look at models of force loaded spring-mass systems based on neuronal modelling and then construct a feedback-control system with separate hierarchies (and deliberately apply latency). But then again, this could lead to a system being created that despite being built out of neurons and delivers the theoretical capability, has nothing in common with actual biological brains.

    I don't know if anyone has tried to develop the canonical models as actual neuronal systems (https://www.sciencedirect.com/science/article/pii/S0896627312009592).

    There is this also:
    "Single cortical neurons as deep artificial neural networks"
    https://www.sciencedirect.com/science/article/abs/pii/S0896627321005018?dgcid=author

    Perhaps start a different thread if this is something worth talking about?
     
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  7. Jaybee00

    Jaybee00 Senior Member (Voting Rights)

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  8. Jaybee00

    Jaybee00 Senior Member (Voting Rights)

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    Anyone have access to the full article? Wondering who funded this.
     
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  9. Snow Leopard

    Snow Leopard Senior Member (Voting Rights)

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    The majority of the talk had little to do with functional motor disorders. The video mostly focused on the fact that our sense of attention or 'volition' during a motor task occurs after the task actually occurs.

    Several signals are observed in the brain during a motor task, firstly a readiness potential that basically lets the brain know a motor task may follow, this is typically around 1 second before but can be up to 8 seconds during some tasks. Then there are several senses of a generation of a task, with the sense of will occurring after the time at which the motor task occurred, yet the individual percieves it as being around 200-300ms before the task. They also devised an experiment that attempted to predict a task based on the readiness potential, then provide feedback to the participant to prevent the task. The 'point of no return' was around 200ms before the task occurred, however many participants quickly aborted the task partway through. He also mentioned that Transcranial Magnetic Stimulation of the supplementary motor areas 200 ms after a task has started can disrupt an individuals sense of when the task occurred. Additional note from me: TMS of the SMA also disrupts the sense of effort during motor tasks.

    The question of functional motor disorders was covered in the first question, but the answer was about why individuals don't perceive there to be a sense of volition associated with the motor movement. Hallett suggests the problem is in the right temporoparetial junction that has been shown to be integrate our conscious attention and sense of volition. But he didn't answer as to why this system may be going wrong, nor why the movements are generated in the first place.
     
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  10. Andy

    Andy Committee Member

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    Comment: Functional neurological disorder and other unexplained syndromes

    "Functional neurological disorder is a syndrome of medically unexplained neurological symptoms. In The Lancet Neurology, Mark Hallett and colleagues review some of the potential explanations for functional neurological disorder and the evidence that supports these explanations. 1

    The paper by Hallett and colleagues, however, is more than a Review: it is also a territorial claim, seeking to expand the boundaries of what should be considered functional neurological disorder. The details of this claim are unlikely to be controversial to any clinician working in the field: the presentations Hallett and colleagues describe are not new, even if they do not fall within the current classifications of the disorder. But the claim is nonetheless remarkable, as even a decade ago it would have been thought to be sheer folly. A good argument could then have been made that functional neurological disorder (or conversion disorder, as it was more formally known) was the most stigmatised of all disorders, even compared with other unexplained syndromes. What would have been the point of expanding the scope of a diagnosis that patients went to such lengths to avoid? 2

    The expansive mood in the Review by Hallett and colleagues therefore reflects a striking transformation in the status of functional neurological disorder. Functional neurological disorder has become a diagnosis that a neurologist might be comfortable to give, and that a patient might be glad to receive."

    Paywall, https://www.thelancet.com/journals/laneur/article/PIIS1474-4422(22)00095-3/fulltext
     
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  11. Art Vandelay

    Art Vandelay Senior Member (Voting Rights)

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    The author of this fawning dross is Richard Kanaan. Not surprisingly, he and Wessely are old cronies.

    I believe the technical term for this is 'circle jerk'.
     
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  12. Jaybee00

    Jaybee00 Senior Member (Voting Rights)

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    Has anyone read the actual paper? I cannot access through sci-hub. Thanks.
     
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  13. Gradzy

    Gradzy Established Member

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    When I was first diagnosed with FND I was directed to Stone’s website.

    All the consultant herself said to me as an explanation for the diagnosis was some very brief waffle about software, as per Stone. Then she told me to check the website out.

    I was instantly suspicious. Then I checked out the website and got much more suspicious.
     
    Last edited: Aug 22, 2023
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  14. Amw66

    Amw66 Senior Member (Voting Rights)

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    Ah so patients are all Buddhist monks ...
    ( power of mind over physical )
     
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  15. Evergreen

    Evergreen Senior Member (Voting Rights)

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    About this bit quoted by @Art Vandelay above from Jon Stone's website about Vogt's recovery stories
    Have they? I was surrounded with them. Bombarded by tales of people doing the same things as me and just having different outcomes.

    One of the most dispiriting experiences I had was reading a book about 50 supposed recoveries. It was so clear there were no patterns, that these people had spontaneously improved. The only things I took away were, ensure I don't have something else like untreated hypothyroidism, and consider diet. Neither helped. I get that some people find recovery stories inspiring; for me, they have the opposite effect. Look! Another person has improved! And it's not you! And they attribute it to things you've done or homeopathy! Super.
     
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  16. NelliePledge

    NelliePledge Moderator Staff Member

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    And in the fine print they are saying they don’t work or they do something home based. They travel but have long rest breaks. Etc etc Ie not recovered back to pre illness level.
     
  17. Arnie Pye

    Arnie Pye Senior Member (Voting Rights)

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    From a UK perspective ...

    Be aware that diagnosis of hypothyroidism is usually restricted to just diagnosing Primary Hypothyroidism (PH). Other forms of hypothyroidism are rarely tested for and rarely treated because doctors are trained that such other forms are rare and thus belong in the "zebra" category which is often ignored. Also note that if a patient has PH they can still be missed for many years because doctors seem to rarely think of it - I don't know why.

    Also testing and dose levels are usually determined by TSH alone these days because "TSH is the gold standard marker for thyroid disease" and setting doses for treatment. And - "If the TSH is in range then the thyroid hormone levels must be okay so we don't have to test them". This is nonsense and leaves many people struggling for years without treatment.

    TSH is produced by the pituitary. But doctors think pituitary problems are vanishingly rare so can again be ignored. There are oodles of thyroid forums on the web if it interests you.
     
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