Controlling movement

How might control over our movements change as we age, and what can we do about it? To answer these questions, Chris Smith spoke to Ann-Maree Vallence, from Murdoch University, Western Australia...

Ann-Maree - We use a non-invasive brain stimulation technique called transcranial magnetic stimulation, and this is a reasonably new technique that allows us to activate the brain cells non-invasively in a comfortable and safe manner. And the technique relies on electromagnetic induction because we know that brain cells are activated through changes in electrical activity, so we can use transcranial magnetic stimulation to induce a magnetic field, that passes through the scalp, which induces electrical current flow in the brain cells and activates them.

Chris - Does it harm them doing that?

Ann-Maree - No TMS induces electrical activity just the way that neurons or brain cells would typically be activated. So it's a safe method.

Chris - And does it turn the cells on or does it turn them off or both?

Ann-Maree - It can do both. It turns the cells on. So if we give a large stimulus then we can get an excitation response or we can see the effect of activating those brain cells. We can also use it to disrupt brain cells and so if someone is performing a movement in this case and we give a big stimulus to the part of the brain controlling that movement, it can temporarily, in order milliseconds, disrupt that activity.

Chris - And how do you focus where that effect happens.

Ann-Maree - Well part of that comes down to the design of the coil that we use to stimulate. It's in the shape of an eight, which I'm sure you can imagine, in the middle of that coil is where the maximum stimulus is delivered.

So that allows us to give a fairly focal stimulus and when we are deciding which part of the brain that we're interested in, in terms of movement we're interested in the primary motor cortex and this is a strip of brain that runs pretty much from your ear to ear. If you take your finger and place it near your right ear and run right along the top of your head to your left ear, that's the motor cortex. So if we hold our coil over that motor cortex or the motor strip, deliver a pulse, we can see the effect in the muscles of the body that we're targeting.

Chris - So you measure the muscle activity electrically, so you can see what the muscles are doing when you do this change in what the motor cortex is doing, so you can see how one is influencing the other?

Ann-Maree - Exactly. So in a typical experiment we would put some recording electrodes over small muscles of the hand for example. We would then use our coil to stimulate the representation of those hand muscles in the motor cortex. And after a very short latency, we can see the twitch in the muscle recorded as you say with electrical activity.

Chris - And how does this help you to solve the problem that you set out asking which is how movements get initially planned, then executed smoothly, and why they fall apart a bit as we get older?

Ann-Maree - We can use this technique to measure how active or how excitable particular parts of the motor cortex are. And so if we compare the excitability of particular regions between younger and older adults, we can start to understand how the brain is functioning in these two age groups. And whether there is some age-related decline in brain function, and that might be associated with age related decline in movement control.

Chris - And is that what you're finding?

Ann-Maree - Yes. So one recent study that we've conducted is actually looking at connections between two motor areas of the brain, the motor cortex and the supplementary motor area. Now this is a brain area that's a few centimeters in front of the motor cortex. And it's important for bilateral movement, so controlling both of the limbs, both of the hands in a coordinated manner.

And what we're finding is that when we probe the connections between the supplementary motor area and the motor cortex with transcranial magnetic stimulation, this connectivity is weaker in older adults than younger adults. And the strength of that connectivity is actually associated with how well they can perform a bilateral task, like using the hands to make a cup of tea or open a jar.

Chris - Do you have any insights as to why you're seeing that and could you for instance go to a brain bank and look at physical brain specimens to see if in people who have obviously now died but would have had these sorts of symptoms, whether you can see any anatomical reason for why you see this functional change?

Ann-Maree - Yeah it's a really interesting question and we're interested in looking at the brain structure. We know that as people age there are structural declines in the brain and we know that the structural decline occurs in motor areas like the ones I've described.

The structural decline tends to happen before we notice these symptoms in movement, the poorer movement. So it would be really interesting for us, in an alive person, to actually measure the structure of these connections by looking at what we call the white matter tracts and seeing whether they can predict a decline in movement control and whether we can also measure the functional decline and its association with movement control.

Chris - And it's one thing to identify why something's happening, it's another to try and do something about it. Do you think this is going to give you any insights into how we can help people, either not decline so much at all in the first place, or if they are at risk of this happening, help them to improve their function in some way, so they don't end up too shaky to write a cheque or make a cup of tea?

Ann-Maree - Yeah that's the overall goal actually and I think we can do that. There are two potential approaches to that. The first is actually to use the technique I've described already, transcranial magnetic stimulation, in a repetitive fashion. Instead of giving one pulse at a time to measure its effect on the brain, we can give hundreds of pulses over the course of several minutes and that has been shown already in a healthy young brain to increase the excitability of the stimulated brain regions.

So the plan to test actually is whether we can repeatedly stimulate the supplementary motor area and the motor cortex and see whether that can in the short term improve movement. If that is the case then that could be a potential therapy, repetitive brain stimulation.

The second approach, which might be more widely available, is to test interventions that we think will improve movement control and go in and probe functional connectivity. And then we have an evidence based intervention to improve movement control.

Chris - Have you got a study population you can look at? Is there anyone who's willing to take part in these sorts of studies?

Ann-Maree - Yeah we actually run a lot of studies here at Murdoch University, we’re recruiting older adults from the local community and they're very happy to participate actually.

Chris - So what, you’ve got an old folks home next door?

Ann-Maree -  Actually we do! But we also target the local community centers, libraries, sporting clubs and we have really good engagement with the aging community. And we feed back to them the results of our studies and have morning and catch ups like that which they really enjoy.