Moving Forward With Prisms: Sensory-Motor Adaptation Improves Gait Initiation In Parkinson’s Disease

Dr. Janet Bultitude

Centre for functional magnetic resonance imaging of the brain, University of Oxford, UK.

Victoria Murphy:

My guest today is Dr. Janet Bultitude from the centre for functional magnetic resonance imaging of the brain, University of Oxford, UK. Dr. Bultitude, a very warm welcome to you, thank you for joining us.

Dr. Bultitude:

Hi, thanks for having me

Victoria Murphy:

Today we are here to discuss a paper you authored in Frontiers in Neurology in September 2012. The title of the paper was ‘moving forward with prisms: sensory-motor adaptation improves gait initiation in Parkinson’s disease’.

What were the objectives of your study?

Dr. Bultitude:

A lot of people with Parkinson’s Disease find that they have difficulty walking. These difficulties can take many different forms, but what we were particularly interested in was the problem that some people seem to have with initiating walking. These patients say that once they get going they seem to be fine, but it’s getting going that is the problem. Scientists and doctors have studied this problem, and we know that when we start walking our body moves forward over our feet until we’re leaning far enough forward that we have to take a step or else we’d fall. From there everything seems to be fairly automatic, but what has been found is that people with Parkinson’s Disease don’t move their body forward enough over their feet to get that initial momentum. This might explain why they have difficulty initiating walking.

We used a simple behavioural training technique, called prism adaptation, that has been shown to adjust balance in stroke patients, and changed it in such a way that it should, theoretically, give people just a little more forwards lean in their body, which should in turn make it easier for patient’s with Parkinson’s Disease to initiate walking.

Victoria Murphy:

How was it designed?

Dr. Bultitude:

We tested how quickly people could step forwards, asked them to perform the prism adaptation intervention, and immediately measured their forwards stepping speed again. So within the same session we could see if prism adaptation changed how quickly they could step forwards.

So now would probably be a good time to explain what prism adaptation is. Prism adaptation is a way of adjusting or recalibrating our sense of the normal relationship between the sensory information we receive about the world, from our eyes and our sense of touch, and the motor signals that are generated in order to interact with it. In this study, people wore goggles that were fitted with prismatic lenses that shifted their vision by about fifteen cm upwards. While wearing these goggles, they had to reach quickly to touch a small target at arm’s length. When you do this, you find yourself missing the target – you aim too high. But if you keep going, after your performed a few of these reaching movements your sensory-motor system adjusts – your body is adapting to the shift and there is a downwards recalibration in your reaching movements. Basically, you’re learning that you need to adjust your movements downward in order to interact with the world. Based on some previous work with stroke patients, we thought that this downwards adjustment in pointing could translate to a slight forwards shift in body posture, and therefore faster forwards stepping.

First we tested the concept with healthy people, and found that upward-shifting prisms did result in faster forward stepping times, as we predicted. We also found that adaptation to downward-shifting prisms, which, if anything, should result in a backwards shift in body posture, had no effect on forward stepping times. This was our control condition. Also, there was no change in backward stepping times for either types of prism adaptation.

This was quite encouraging, so we went on to test 16 patients with Parkinson’s Disease, and we found that after five minutes of adaptation to upward-shifting prisms they too showed faster forward stepping times.

Victoria Murphy:

What types of patients were included?

Dr. Bultitude:

We tested 16 patients with Parkinson’s Disease.

Victoria Murphy:

What were the study endpoints?

Dr. Bultitude:

We measured stepping times using a very simple set-up. Patients held a lever that was attached to a microswitch in the floor. As soon as they heard the word ‘forward’ or ‘backward’, which was played by a computer, they took a step in the appropriate direction, which would move the lever and activated the microswitch so that we knew how quickly they had taken the step.

Victoria Murphy:

What were the results?

Dr. Bultitude:

Healthy people had an 8{cf2c27d335602139ec9071daca508545599ba8f9ca09b366fd00e5c28736f208} reduction in forward stepping time, and patients had a 10{cf2c27d335602139ec9071daca508545599ba8f9ca09b366fd00e5c28736f208} reducting in forward stepping time.

Victoria Murphy:

Are there any limitations to the study?

Dr. Bultitude:

Yes. We consider the results of this study to be a promising proof-of-concept, which means that we have good evidence that, in principle, prism adaptation might be a quick and simple way of improving gait initiation in patients with Parkinson’s Disease. But before we could be really confident of this we need to do further research to address two limitations of our initial study.

First, we only tested upward-shifting prisms in the patients who had Parkinson’s Disease. That is, we only tested the condition that we thought might help them. To be confident that it was prism adaptation that was reducing the patient’s forward stepping time, we need to perform a study in which we compare prism adaptation to some sort of sham or placebo treatment. A standard control condition for prism adaptation is to ask patients to perform the reaching task that I described before, but while wearing neutral lenses that don’t shift the visual field, and therefore don’t result in this recalibration of the sensory system. We can compare the effect of this sham treatment to the effect of the real prism treatment to see whether it’s really prism adaptation that is helping, or just something to do with our winning personalities influencing patient’s stepping.

Second, we can’t be sure that the stepping measure that we used in our study is truly reflective of real-world walking. So we need to test the effects of prism adaptation on posture and walking in patients with Parkinson’s Disease using much more refined techniques that give a better picture of how the person can get about in the real world. I’m currently planning more research in gait analysis labs in Lyon in France, and Dartmouth in America, where we are measuring things like standing balance and making detailed analyses of different aspects of patients’ walking by using treadmills and motion trackers.

This research is taking place at the Intstitut National de la Santé et de la Recherché Médicale, which is the French Government Medical Research organisation, and the Geisel School of Medicine, which is part of the Dartmouth-Hitchcock Medical Centre.

Victoria Murphy:

What conclusions can be drawn from these results?

Dr. Bultitude:

We can conclude that prism adaptation may be useful in helping patients with Parkinson’s Disease address one aspect of their walking difficulties. This is quite exciting because prism adaptation is very easy to administer and inexpensive, and patients can perform it in their own home. Problems with walking is a symptom that contributes dramatically to Patients’ sense of dependence and disability, so anything that can be done to address these difficulties could make a dramatic difference to their lives.

Victoria Murphy:

Can these results be considered conclusive?

Dr. Bultitude:

While we believe these results are quite exciting, further work is needed before we’ll be urging doctors to hand out prism goggles to their patients.

Victoria Murphy:

Dr. Bultitude, thank you for joining us today, it has been a pleasure.

Dr. Bultitude:

Thank you very much for having me.

To access the full article please click on the link below,

http://www.frontiersin.org/Movement_Disorders/10.3389/fneur.2012.00132/abstract

 

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