Thread by @FndPortal

So here’s a potentially productive conversation:

is Functional Neurological Disorder really a structural disorder or a functional one?

Should it be considered “psychological”?

Do we even know what it is?

(thread)

https://twitter.com/davidtuller1/status/1213518599018565633

To respond to Dr Tuller’s first question: how is FND different from other neurological disorders?

In some ways, it’s not! It creates real disability, with symptoms often comparable to other neuro disorders like MS, and the source of that dysfunction is the brain.

This is part of why some patients have argued against an exclusively psychological formulation: because it’s not just a subjective belief that you have, say, a gait disorder. You actually do.

IMO, FND should be all rights be a fully paid-up member of the Neurological Disorders Club. The fact that it isn’t (yet) widely recognized as such reflects a few differences:

(FND experts, plz jump in here if I’ve erred or if you feel something I’ve said is not quite right)

1) FND has a different character than other neuro disorders. It’s not (directly) due to a pathogen, or genetic abnormalities, or autoimmune issues where your immune cells eat the myelin on your spinal cord or that kind of thing.

Following that, it’s not typically visible on MRI. My understanding is that’s because brain changes in FND at least typically begin at a micro level, too small for typical MRI to pick up.

Although both imaging technology and analysis techniques are getting better, and with these researchers are now able to examine differences at both the functional (micro) and structural (macro) levels.

en.m.wikipedia.org/wiki/Voxel-bas…

(Neuroimaging is super not my strong point, so anyone with that background, please feel free to clarify or correct!)

(@JalilianRozita could perhaps speak to the specifics of this?)

Anyway, neurologists are sometimes skeptical because FND symptoms can be “inconsistent”, which implies they’re not due to the same kind of permanent structural damage that you’d see with something like a brain lesion.

Then (and this is where I think the scales in many a doctor’s mind start to tip heavily) symptoms sometimes appear to be driven or influenced by psychological factors.

FND patients as a group have a very high rate of adverse life events, from neglect to abuse to physical injury and chronic pain.

Although importantly not everyone seems to have a psychological history, which I think is significant.

thelancet.com/journals/lanps…

So, having that picture: “inconsistent” + no findings on MRI + past history of mental illness seems to suggest to some neurologists that this is REALLY a fully psychological disorder, AKA not a neurological one...

AKA a problem of the mind not the brain, and thus not my problem, please go find someone else to fix your crazy.

We’ll leave the stigmatizing attitude re: mental illness for another time...

But it’s not fully psychological anyway! And that’s what I mean by saying that FND is bigger than either psychiatry or neurology.

“Fully psychological” also doesn’t explain how people develop these symptoms after injury, as I and many others have.

ncbi.nlm.nih.gov/m/pubmed/24439…

So what is functional neurological disorder, then?

The evidence suggests that it’s a (yes) neurological disorder, and that the dysfunction lies in multi-modal brain networks at the top of the neural hierarchy.

Part of this is the so-called “limbic system”, which classically has been associated with emotions.

AHA! PSYCHOLOGICAL! 🙄
(hang on)

But it turns out the brain systems affected in FND also handle everything from motor control to attention to memory and visual perception and monitoring the state of the body (the interoceptive network).

Multi-modal brain networks. 👍

So that reflects a general truism of the brain, which is that most brain areas don’t do one dedicated thing, they do like 9 different things.

That’s prob why people can develop the same neurological symptoms from a nasty divorce or a car accident:

ncbi.nlm.nih.gov/m/pubmed/29868…

Because there are *no exclusively emotional networks in the brain*. A physical or emotional disruption can produce the same symptoms because they screw up the same brain networks, which are doing multiple things at once.

So that requires us to recognize that a psychological stressor need not be present for someone to get FND, but also acknowledge that it can happen that way, and that the disorder is sensitive/responsive to both emotional and sensory stimuli.

That also explains why symptoms can be “inconsistent”: it’s not the same as a lesion in motor cortex, which in one spot would reliably impair your ability to say, move your left leg.

The problem is higher up in the hierarchy, in the areas that govern deployment of other systems.

(Specifically these areas are concerned with attention and action initiation)

That also explains why symptoms can recede with distraction: because you’ve momentarily occupied the dysfunctional parts of the brain with something else, and they’ve stopped interfering with the normal operations of the hierarchically lower areas.

Like when a micromanaging boss takes the day off and everyone gets more productive.

That attentional-emotional-bodysensing character is also why symptoms that seem really different, like certain types of tremors and paralysis and seizures and speech difficulty, frequently co-occur in the same patients, + are considered symptoms of FND.

Because they share common qualities reflecting a shared underlying dysfunction in the same brain networks.

From a patient perspective, this updated understanding of the brain also tends to make sense. It jives with our stories and experience of how the disorder started: usually some disruptive episode amplified by attention towards the body. And then we couldn’t get un-stuck.

From a not-patient perspective, many of our stories conversely slot nicely into how computational approaches to the brain theorize how these things might happen. It all starts to come together.

(Andy Clark @fluffycyborg and Karl Friston have both written on this)

academic.oup.com/brain/article/…

global.oup.com/academic/produ…

Regarding “structural vs functional”:

FND is at LEAST a functional disorder, and appears to be in some cases a structural one. The question is “why would it be structural?”

There isn’t a definitive answer to this yet, but one possibility is that the structural changes develop out of the initial functional ones.

Neuroplasticity is kind of the central operational mechanism of the brain AFAIK, so if someone loses their ability to walk due to a functional problem, those brain areas will atrophy because brain cells there aren’t firing as they used to. Use it or lose it.

That can lead to subsequent changes in morphology, + eventually those changes will be visible at the macro level.

There are other possibilities too though. I think there’s a review of that topic here.

ncbi.nlm.nih.gov/m/pubmed/31146…]

Ok

So now we’re getting out of the evidence and into my personal opinion, but my take is that FND is informative about the least-understood aspects of the brain, especially around consciousness.

And the nature of FND suggests two major things about how to think about this topic

1) The words we use to delineate one thing from another (emotion, perception,action) in our folk understanding of the brain don’t map very well into what the brain is actually doing.

2) At a more academic level, while there are some differences between psychiatry and neurology, FND sits squarely at the nexus between the two, and suggests there’s really no simple binary. They’re more like two different dimensions of a 3D concept of brain function.

Id argue the delineation between the two is causing a lot more confusion than clarity here, especially for a disorder so bound up with action and the body.

I’m actually pretty excited bout where FND science is right now, cuz it means diagnoses for people who need them, it differentiates FND from the collective mass of other undiagnosed / rare disorders, and it’s kind of illuminating the architecture of consciousness to boot.

You can read something like this and see how FND might be relevant:

psyarxiv.com/6snfm/

So that’s my understanding. It’s both neuro and psych, a functional disorder that can also be structural because the brain is plastic, and suggests that an overall re-appraisal of how we think about the brain and body is overdue.

🧠💪❤️