Measuring brain plasticity

Monday 11 February 2013 5:50PM (view full episode)

Heidi Johansen Berg from the University of Oxford has studied ways of stimulating parts of the brain. Stimulation techniques have been used to 'steer the recovery' of stroke patients as well as to increase the pace of learning for healthy individuals.


Norman Swan: The University of Oxford in the UK has a world-leading lab investigating brain plasticity. It's run by Professor Heidi Johansen Berg.

They use magnetic resonance imaging—MRI—to look at the brain in action. And have studied juggling!

Heidi Johansen Berg: That's right, so we're interested in what happens when healthy people learn new skills or have new experiences. So if you learn a new skill, like playing the piano or juggling, that can change the structure of our brains. So we took people who couldn't juggle and trained them to juggle over a six-week period, and when we scanned their brains before and after that training we found that a particular bit of the brain had grown in size, but also that the pathways, the brain fibres that connect that brain area to other areas, had changed their properties, had effectively got stronger. And interestingly those areas that were changing were those areas that we know were involved particularly in visual abilities, and when people reach for objects in the periphery of space. So exactly those kind of functions that you think should be trained when someone learns to juggle.

Norman Swan: So it was both behaving like a muscle and a network.

Heidi Johansen Berg: Exactly. So there's this idea that if you train something repeatedly it can grow, it can get stronger, but also the special architecture, if you like, of the brain is that it is made up of these vastly complicated networks.

What was novel about this study was looking at these connecting pathways, the white matter, so these are the fibres that allow signals to pass between different brain areas and connect up those bits of the network, and it hadn't previously been shown that those could change their structure.

Norman Swan: And the better somebody had learned juggling the better the network?

Heidi Johansen Berg: Well, curiously not. We were expecting to see that. By the end of the six weeks some people could barely do the three-ball cascade that they were being taught, whereas others could do five balls, could do it forwards and backwards and all kinds of fancy tricks. You'd think, therefore, that that variation in skill would relate to the brain structural change. But we didn't actually find that. So one of the things that we're doing now as a follow-up is try and see whether maybe what's more important is simply how long you spend training. So now we're doing a similar study but people train for different amounts of time.

Norman Swan: Because what it might be is that the act of training changes the brain rather than the end result.

Heidi Johansen Berg: Yes. It might be that the actual learning of the skill might be more related to these fine changes in the strength of connections in the synapses between the cells.

Norman Swan: Of course that's critical, because if you've had a stroke and somebody trains you, you're not going to thank them when they tell you, well, that bit in the brain has got bigger, isn't that fantastic, when you still can't walk.

Heidi Johansen Berg: In the clinical setting these things are only relevant if they translate into benefit for the patients.

Norman Swan: Tell me what you've been doing with people with stroke.

Heidi Johansen Berg: We've been looking to see whether we can use these same imaging techniques to observe what happens in the brain of people as they recover, but also potentially more excitingly to see if we can steer that recovery through brain stimulation. We can use very small electrical currents to stimulate people's brains non-invasively, so this is just by placing rubber pads against the scalp and passing a small current, say in the order of one to two milliamps, between two of these pads, and that has the effect of stimulating the underlying brain tissue. The imaging can tell us which bits it would be better to increase, potentially which bits it would be better to decrease in order to steer the brain along a particular path of recovery.

Norman Swan: So where you put the jumper leads is important.

Heidi Johansen Berg: Yes.

Norman Swan: What problem have you studied in people with stroke?

Heidi Johansen Berg: What we focused on is movement, and particularly hand and arm movement. There are conventional approaches to physiotherapy and motor training that are somewhat effective. What we're trying to do is enhance those effects with brain stimulation. So it's not that we think that the stimulation itself will magically cure these people's brains, but rather that this type of brain stimulation affects the brain in such a way that it makes learning or plasticity more likely to occur. So we know, for example, that it alters certain neurochemicals in the brain in such a way that learning is more likely to occur.

So what we typically do is have people undergo a fairly conventional physiotherapy session, a motor training session, but while they're training, while they're practising their movements, their brain is being stimulated. And the thinking is that therefore the normal changes that would typically happen in their brain will happen more strongly, will happen more quickly.

Norman Swan: And what have you been finding?

Heidi Johansen Berg: The clearest thing is that all patients are benefiting from this intensive physiotherapy. That in itself is actually interesting because these are all patients who are many years post-stroke and in many cases the physios are telling us there's not a great deal of point in working with this person, they're as good as they're going to get. But yet with this two weeks of intensive training they're all getting significantly better. Obviously the key thing from our perspective is does the electricity make them get even more better? At this interim stage there's a small but significant effect. But certainly when you see these patients and how motivated they are to get better, what looks to us on our graph to be a tiny effect, for them might make an enormous difference, you know, it might mean that they can eat for themselves or that they can tie up their own shoelaces or put on their own shirt.

Norman Swan: And you're studying brain stimulation in healthy people to see whether or not it turns them into Einsteins…

Heidi Johansen Berg: That's right. So we're just studied in a very small way so far which is that, you know, if you have people learn a new motor task—in our case it was a sequence of button-presses—they're learning to press these keys in sequence, and just like with the stroke patients, as they're performing that motor learning we're stimulating their brain in a way that we think will make it more likely for their brain to learn. And what we find again is this very subtle effect such that those who are getting stimulated learn that sequence significantly faster.

This is kind of exciting. You can think of all the sorts of real-life situations where that could be applied. You can imagine a class full of children all wired up to their brain stimulation, learning their times tables faster. You can imagine athletes wired up to stimulators, learning a new sporting skill more quickly.

Norman Swan: Raises all sorts of ethical questions as well.

Heidi Johansen Berg: It certainly does, yes.

Norman Swan: Of course, unlike a drug, if you put the electrodes in the wrong place they might decrease their ability.

Heidi Johansen Berg: Yes, certainly that's something that we're acutely aware of in the stroke setting, because you can have opposite effects of these types of stimulation depending where you place the electrodes, it's really important that we're looking on an individual patient basis as to whether we're making things better or worse. It's also very likely to be the case that the same pattern of stimulation will not be effective for every single stroke patient. Different patients' brains recover in different ways, so what we're trying to move towards is defining a collection of brain scans and tests that we could do when a patient comes into the clinic, and that will tell us what would be the most effective pattern of stimulation for that individual patient.

Norman Swan: And you're moving into physical activity?

Heidi Johansen Berg: Yes, that's right. So one of the most effective types of intervention that one can do to improve your brain power is actually to exercise your body. And there's very good evidence that particularly as we get older and our brain powers decline, one of the best ways to guard against that is to keep the body active and in particular to engage in cardiovascular activity which works the body. So what we're currently doing now is a big study in which we're taking older people who don't typically exercise and enrolling them on an exercise regime where they'll go to the gym a few times a week, and we're scanning their brains and doing lots of tests of their thinking abilities before and after a three-month period of going to the gym regularly, in order to really pin down what those benefits look like and what brain changes seem to be mediating those benefits.

We're doing a pilot study in younger people ranging from about 20 to 60, and what we're seeing there is that even in that young population if you take sedentary or inactive people, force them to go to the gym every day, then you can see changes in their brains. In particular there's a part of the brain called the hippocampus which seems to grow in size after that kind of physical training…

Norman Swan: Which might affect memory.

Heidi Johansen Berg: Which might affect memory and all kinds of thinking abilities but particularly memory. And what we see in that population is that that growth of the brain is particularly prominent in the older people. So it seems that there's more scope for this type of physical activity training to affect older brains, which are potentially on a sort of downward decline.

Norman Swan: The other aspect of physical activity is emotional and psychological, and people are using it to both prevent and treat depression. And there are parts of the brain not far from the hippocampus that we know are affected by emotions such as the amygdala. Are you looking at that as well to see whether or not you're actually changing one of the sources of emotion?

Heidi Johansen Berg: Yes, absolutely, because as you say there's very good evidence that physical activity alleviates depression, so we're assessing depression along with all of our thinking scales. Also, interestingly, in our study on younger people that I mentioned, the particular region within the hippocampus that seemed to be showing the greatest effect is a region which is particularly involved in stress and mood, so it might well be that emotional effects are one of the factors that's mediating the improvements that we see.

Norman Swan: Professor Heidi Johansen Berg heads the Plasticity in Disease group at the Oxford University Centre for Functional MRI of the Brain.


Heidi Johansen Berg
Plasticity and Disease Group, University of Oxford Centre for Functional MRI of the Brain (FMRIB)

Further Information

Plasticity in Disease Group


Dr Norman Swan
Nick Ridout