Why vegetative state patients can't move

Why is it that some people in persistent vegetative states can be conscious but unable to move?
27 October 2015

Interview with 

Dr Davinia Fernández-Espejo, University of Birmingham


Sometimes severe head injuries can leave a patient in what is dubbed a Post Surgerypersistent vegetative state. But recently, using a brain scanning technique called fMRI, scientists were able to show that some of these people are conscious and capable of communicating with them, but were just not able to move. Now Davinia Fernández-Espejo's has uncovered why - there's a 'disconnect' in the brain which prevents the thalamus - a relay station in the centre of the brain - and the motor cortex - the area of the brain that produces movements - from exchanging information. Graihagh Jackson caught up with her to hear how...

Davinia - So in this paper, we were looking for structural damage in the brain of patients who appear to be in a vegetative state. This is, they don't show any external signs of being aware of themselves, of the environment. But we do know that some of these patients are actually fully conscious. This is a small percentage of them and are just incapable to move. So, the first step we study was to try and identify awareness using these fMRI techniques asking them to imagine they were playing tennis, imagine they were moving their hands. Once we had a patient who we could confirm they were actually aware then we did the second part of the study.

Graihagh - And then my understanding is you also looked at healthy people and mapped what bits of their brain lit up as well.

Davinia - That's right. So, up until now, we were not entirely sure what the differences are between just imagining a movement or actually, physically performing that movement. And that was key in this study because this is the difference between the things that they can or can't do - these patients. So, they can imagine a movement, but they can't actually perform that movement. So we needed to see the difference between these two processes to know what were the areas are key for you to give this step further and actually move. And we found that there is a significant pathway which is the one connecting the thalamus which is the small region, kind of in the deep of your brain and the motor cortex which is the region that ultimately is going to send the signal to your limbs to move. So in a way, these two regions appear to be disconnected so the information can't travel from one to another and that's what's stopping these patients from being able to actually externally move.

Graihagh - That surprises me because you would've thought patient to patient, the structural damage in the brain would be very different, but you think it's down to this one sort of connection.

Davinia - Well, that's a good question. So, in this study, we focused on patients with a very specific type of damage which is traumatic brain injury from a car accident. What we don't know yet is whether this specific damage is going to appear also in patients of different aetiologies, and that will be the next logic step to this study.

Graihagh - What happens in these patients that means that there is that disconnect in the brain?

Davinia - So basically, when we're talking about a car accident, there's speed and sudden deceleration. What happens is that the fibres that are connected from regions of your brain break in the process. So, that ends up leaving regions that can't speak to each other again.

Graihagh - How common is this type of injury?

Davinia - It is very common. They're quite recent, so we only see these patients in the last few years. This is because we are talking about very severe accidents that before all the advances in the medical care wouldn't have survived the accident.

Graihagh - That's really interesting. I mean, I suppose it's great to show that we've had so much progression in this. But equally now, we've got a whole new other caseload of difficult things to solve.

Davinia - That's right. We're getting really good at solving problems in our organs and our body, but the brain is still something we're still kind of trying to understand.

Graihagh - Does that mean then, now that you've identified this blockage, that you can do something about it. Might there be a treatment down the line that could help these patients?

Davinia - Yeah and that's the most exciting thing about this finding. We're still very early in that direction, but I think it's a good first step. So, we can't regrow those fibres that are gone. That can't happen but we can do something to make those connections that are still present to work harder to try to compensate for the damage. There are several ways we can do this. We're still studying what's the best approach, but anything that you can think that could make those fibres that are still there work harder and make these two regions talk to each other could help these patients in the future.

Graihagh - How might you be able to make these connections work harder?

Davinia - So, there are several possibilities. One possibility could be a pharmacological treatment and there's also a number of brain simulation techniques that can help give these regions a little push to try and work a little bit harder.

Graihagh - So, how far away do you think are we from this type of thing? I know you said this is sort of a good first step. How long are we looking at here?

Davinia - Yeah. That's difficult to tell. We're starting to try some of these ideas about how to simulate some of these regions now. So, we're still a few years away from knowing the answers to this.


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