I’m Matthew Rushworth, I’m a research scientist. My particular interest is trying
to understand the prefrontal cortex, a part of the brain. The prefrontal cortex like many
areas in the brain is actually a mosaic of different areas. Each little tile in this
mosaic of areas has a different job to do and one of the things that we are interested
in is understanding what all of the different parts of the prefrontal cortex are doing,
what contribution they are making to our mental life.
So, to give you an example, recently we have been looking at a particular part of the prefrontal
cortex, we call it the lateral orbitofrontal cortex and we think this brain region has
a very special role to play in discerning what events in the environment cause each
other so how does one thing cause another thing? What events lead to which consequences?
In order to try and study this one of the first things we were doing was looking at
macaque monkeys and we were looking at activity in the orbitofrontal cortex of these macaque
monkeys while they were performing very simple tasks. The tasks that we give them are a little
bit like a computer game for a monkey. What they are doing is that they are looking at
a computer monitor and they see several different visual patterns that we call stimuli that
are presented on their computer monitor. Their job is a very simple one, to work out which
is the best pattern to pick, to reach out and choose with their hand and if they pick
a good pattern then they get a small juice reward. What we are interested in is how the
animal links together the pattern they choose and the good consequence; the juice reward
that they get afterward. It turns out that this ability to make those links, to make
those associations is reflected in activity that we can measure in the orbitofrontal cortex.
One of the things that we have also been doing is looking at what happens when the orbitofrontal
cortex isn’t working properly. What are the consequences for behaviour and we can
try and investigate that by making a very precise disruption to the orbitofrontal cortex,
we can do this by using a special surgery that stops the specific brain region from
working in the normal way while leaving the rest of the brain working just at it would
do in every natural situation. There is a consequence of this type of manipulation.
We can see that animals are no longer so good at linking one event to another. They are
no longer are so good at working out which of these patterns that we are showing them
is the one that leads to the juice reward. This is telling us that this particular brain
area is doing a very basic but also a very important job in our mental life, enabling
us to see what events cause which other events in the environment around us.
Since we made this discovery we have gone to see if it has any relevance for understanding
how the human brain works because a large part of our work in the lab is actually working
with human volunteers. There have been a couple of different ways in which we have taken the
work forward with human subjects. One of them has been to put ordinary healthy humans into
MRI scanners and to try and record activity in the human brain. We are able to get a rough
sense of where activity changes in our human volunteers. We have been able to discern a
similar pattern of activity in the orbitofrontal cortex of our human volunteers while they
are performing similar type of computer games. Only now instead of winning small amount of
juice they are winning points that are going to be translated into money at the end of
the game. A second way that we have tried to take the
research forward is to collaborate with other researchers working with human patients who
have suffered strokes. Sometimes when people suffer a stroke they lose the ability to use
their arm or their leg and to move around in the normal way. Sometimes a stroke can
affect the prefrontal cortex, the areas that we are interested in. In such situations people
suffer a different type of disability. They might be able to move normally, they might
be able to see and to hear normally but they don’t seem to be capable of independent
living in the same way and it’s difficult for us sometimes to understand what it is
that has gone wrong. Some of our recent research suggests that this process of working out
what causes what, is one of the things that’s compromised in these patients, if the stroke
affects this particular region that we have been investigating? This is something that
we hadn’t realised before. Another way in which we are trying to take
the work forward is looking at how people with various different psychological illnesses
such as depression makes sense of cause and effect in the world around them. One of the
things that we know sometimes happens in depression is that people assume too much responsibility
for an undesirable outcome, some event that perhaps they haven’t really being causally
responsible for and so what we are interested in doing now is seeing if our understanding
of how the orbitofrontal cortex works and how we work out cause and effect in the normal
healthy brain, if that has any relevance for understanding how this ability may sometimes
go wrong in psychological illnesses.