Anosognosia for hemiplegia and types of body representation

another attempt to popularise what I do!

Continuing the theme of providing popular summaries of my papers today I’d like to talk a little about anosognosia for hemiplegia and some implications the disorder has for understanding how we represent our own bodies.

Given the very pompous nature of the name “anosognosia for hemiplegia” [MD’s are even better than philosopher’s at playing power games by making up words ] I doubt that its meaning is at all transparent. ‘Anosognosia’ refers to a patient’s lack of knowledge about some problem with their body. In the medical context the most striking examples pick out patients who seem to lack knowledge of a disorder so overwhelming and severe that it is baffling how they could miss it. The most shocking case being Anton’s syndrome or “blindness denial” sufferers of which although clearly blind nevertheless claim to be able to see perfectly well. “Hemiplegia” means half paralysis and refers to cases where either the left or right side of the body is paralysed. I take it that you know what ‘for’ means, so by now you may have guessed that ‘anosognosia for hemiplegia’ refers to patients who lack knowledge about their paralysis- they are paralysed down one side of their body but they do not know this to be the case. The name, of course, comes from Babinski of defecating Maxwell fame (yes I watch the big bang theory; no I don’t think it is offensive to nerds).

So the important thing is that patients suffering from ansognosia for hemiplegia (AHP) are paralysed but they don’t know it. When asked why they are in hospital they don’t mention their paralysis, when asked if they can move they say that of course they can (‘how else could I scratch my right arm?’ (Fotopoulou et al. 2008). They also act as if they are not paralysed; when asked to lift a try of glasses they typically grab the tray from one side, as if to lift with both hands. Patients who are paralysed but aware of this problem grab the try at the centre when asked to perform such actions.

Overall a scary situation to be in, made all the worse by the fact that AHP is one of the least serious symptoms such patients experience following stroke. This is not to say that the symptom isn’t dangerous, it is, but it typically remits after days or weeks. After it remits patients say different things about their experience. Some patients claim that they knew they were paralysed all along and deny their previous denials, so to speak. What are we to make of this? Did they know they were paralysed or not?

The answer, I suspect, is both. To see why we need to look more closely at what patients say about their paralysis. Whilst it is defining of AHP that patients deny their paralysis, it is also true that in some circumstances they temporarily acknowledge that they are paralysed. They do so when repeatedly confronted on their inability to perform tasks which require the use of both hands or when cold water is squirted in their ears (the reason for this is complex, for now suffice to say it changes how patients can direct their attention). When patients do come to acknowledge that they are a paralysed this insight only lasts a short amount of time, 20 minutes or so. Very quickly AHP patients seem to lose this knowledge about the state of their body. What these examples suggest is that somewhere in there is the knowledge that they are paralysed, but this knowledge isn’t used in most circumstances.

Why don’t they access this knowledge? Well in fact I think this isn’t quite the right question, because in one sense they’re not failing to access this knowledge about the current condition of their body, because no one would check the current condition of their body in this circumstance. If I ask you right now if you are paralysed you don’t need to check to find out. You can answer based on knowledge of what your body is usually like. This is what the AHP patient does. When asked if they are paralysed the AHP patient asks based on this knowledge- they’ve not been paralysed before so why would they think they are paralysed now?

We have then a different question to ask about the AHP patient. Why doesn’t knowledge about the current condition of their body, which we know they have- at least when they temporarily acknowledge their paralysis, help them learn that they are paralysed? Why doesn’t this update their knowledge of what their body is usually like?

If we can answer this I think we will have done a huge part of the work needed to understand why people with AHP don’t know that they are paralysed. There is also, as it turns out, a lot more work we can do with this distinction between knowing what your body is like now and knowing what it is usually like. But we can get to that next time.

With love

DrNPC

My paper on this is: Carruthers, G. (2008). “Types of body representation and the sense of embodiment.” Consciousness and Cognition 17(4): 1302-1316.

And others using this distinction: Carruthers, G. (2009). “Is the body schema sufficient for the sense of embodiment? An alternative to de Vignemont’s model.” Philosophical Psychology 22(2): 123-142.

Carruthers, G. (in press). “Toward a Cognitive Model of the Sense of Embodiment in a (Rubber) Hand.” Journal of Consciousness Studies.

Reference:

Fotopoulou, A., M. Tsakiris, P. Haggard, A. Vagopoulou, A. Rudd and M. Kopelman (2008). “The role of motor intention in motor awareness: an experimental study on anosognosia for hemiplegia.” Brain 131(12): 3432-3442.