Unilateral Spatial Neglect
Actually cool, learned about this in PSYCH101.
Slide 01 - Professor James Danckert. Cognitive Neuroscience Research Area
I trained as a Clinical Neuropsychologist in Australia and came to Canada to do Postdoctoral Research at Western University in 1999 — and just never left! The roles of a neuropsychologist and a Cognitive Neuroscientist are related, but both aim to understand the relation between brain and behaviour, but are also quite distinct. As a clinical neuropsychologist, the aim is to evaluate cognitive function in an individual patient. This might be important for diagnosing an illness or for tailoring a rehabilitation plan to help the patient compensate for any lost function. In contrast, the neuroscientist is interested in probing the functions of the brain simply to understand it better. The questions asked are broader, the tools used are more varied and sophisticated, and although there ultimately may be a practical outcome of the work, it’s not a necessary part of what we do.
Slide 02 - How did you become interested in research?
One of my first research interests began from a clinical syndrome. Known as unilateral spatial neglect, patients with this syndrome behave as though the left half of their world has simply ceased to exist. They may eat food only from the right side of a plate. They might dress and groom only the right side of their bodies. And this can seem quite bizarre with a patient putting one sleeve of a shirt on (the right sleeve) and then claiming to be finished while the other half of their shirt dangles behind them.
Slide 03 - What happens in Unilateral Spatial Neglect?
Neglect is a not a problem of basic perception. The patient can see normally. What has gone wrong for the patient is that they can no longer create a full and accurate representation of the world. We test for neglect clinically at the bedside using simple pencil and paper tests. The easiest way to see the disorder is on tests of figure copying. We might show the patient simple line drawings of objects and ask them to make a faithful copy of it on the page. You can see that the patient clearly knows what it is that they are copying but leaves off details on the left side. This can be true for the left side of objects no matter where they are in space. So in copying these figures, the patient omits the left half of objects even when they are on the right side of the page. The most glaring example here is the left half of the apple missing from the tree on the far right side of the page. Again, this suggests that the patient doesn’t have a problem seeing per se, and they also have no problems in understanding what they’re looking at. They know what daisies and apples and cars are. They just can’t represent the left side of them.
My earliest work in neglect patients followed on from the prominent theory of the day which suggested that neglect arises as a consequence of failures to direct attention to the left side of space. This is still the dominant theory. One study in particular, though, fascinated me. This came from Marshall and Halligan in 1988 in which they examined a single case and asked the simple question, “What happens to neglected information?” They showed the patient two houses one above the other. Their trick was that one of the houses was shown to be on fire on the left side. The patient neglected that information and claimed that both pictures were identical. Next, they asked the patient “Well, which house would you prefer to live in?” The patient chose the house that was not on fire at above chance levels justifying her choice by saying, “Well, this one seems roomier, particularly in the attic.” And that suggested that neglected information was not completely lost and was available for use in decision making. We followed this up in my Ph.D. showing that not only could neglected information influence behaviour, typically we look at speed and accuracy as our measures of choice, but that it did so in a goal-directed manner.
Slide 04 - Is there a treatment that can help correct Unilateral Spatial Neglect?
In my postdoctoral years I got the chance to work in France for four months with a team led by Yves Rossetti who had pioneered studies using prism lenses to help rehabilitate neglect. These glasses shift vision in one direction or another. For the neglect patients we shift their vision further to the right, which sounds like a bad idea until you think through the consequences. We ask the patients to point to objects while wearing the prisms. When they do this, their pointing movements miss the targets because vision has been shifted by the prisms to the right. The brain notes the error and corrects for it. So with prisms that shift vision to the right, the brain now starts saying, “Go left, go left, go left!” When prisms are removed the brain is still saying, “Go left!” So now the patient’s movements and attention are drawn to the left side of space, that region that they had been neglecting up until now.
The work on prisms was extremely promising. Over a number of years and studies from many labs it seemed as though prisms could improve the deficit in attention, thought to be the primary cause of the disorder. But we found that this was not entirely true. We used stimuli known as chimeric faces, essentially a mash-up of a smiling face and a neutral face. With two such faces placed one above the other healthy people normally say that the face shown smiling on the left looks happier. This is likely due to the right hemisphere being more involved in emotional processing. Neglect patients on the other hand say that the face shown smiling on the right looks happier presumably because they are neglecting the left side of faces. We tested one patient using a task like this before and after prisms. We monitored eye movements and showed that before prisms, as you would expect, the patient only looked at the right side of the face. After prisms, he now looked at the left side of the face as well. But when we asked him which face looked happier he still said the one shown smiling on the right. So we’d changed his eye movements which is an indirect measure of attention, but we had not changed the way he represented the world. He was still biased to favour the right side of things.
Slide 05 - So what is the current understanding of Unilateral Spatial Neglect?
So this led us to think that problems with attention are not enough to explain the neglect syndrome. We thought that a better model of neglect would be to suggest that the patient fails to build and update accurate representations of the world. What do I mean by representations? Well, it’s not possible for you to see, hear, smell or feel everything that is out there in the world at any given moment. Your brain, awesome as it is, just can’t cope with that flood of ever-changing information. To solve this problem, the brain creates models of the world; condensed representations that help you cope with the vast amount of information and guide behaviour optimally. A key thing about such models is that it must be flexible enough to update when things change.
But how do you go about testing such a high level, abstract concept? Well, we turned to the children’s game of rock, paper, scissors. We had patients play against an opponent that had a bias. The computer played rock eighty percent of the time. If you can represent that accurately, then you can exploit it. If you know ahead of time what your opponent will do, then you can easily beat him. It turned out that our patients could not beat the computer even when it was playing such an obviously biased strategy. But things got murkier from there. Not only did neglect patients fail to win at rock, paper, scissors, but so did patients with right sided brain damage, but without neglect. So part of what we do now in my lab is geared towards understanding this finding.
Slide 06 - Why do you like being a researcher?
For me, this is the most exciting thing about being a researcher, you never know where the data will take you and no single study is ever capable of completely answering a question. We get part of the way there and then go back to the drawing board to try and fill the gaps our last experiment couldn’t fill. And that highlights something else about science that I think a lot of people are surprised by. It’s an incredibly creative experience.
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