Making moves

20 September 2019
Presented by Katie Haylor.

WALKING-CITY

WALKING-CITY

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This month - what’s going on in the brain that allows us to move? How might control over our movements change as we age? And why do armies march in time with each other? We're mulling over the neuroscience of movement. Plus, we’ll be taking a stroll through the latest neuroscience news, with the help of local experts.

In this episode

Brain schematic

01:24 - How much of a risk taker are you?

We tuck in to some neuroscience news morsels with our local experts, Helen Keyes and Duncan Astle...

How much of a risk taker are you?
Helen Keyes, ARU; Duncan Astle, Cambridge University

Joining Katie Haylor to check out the latest neuroscience news stories are psychologist Helen Keyes and neuroscientist Duncan Astle. First up, Helen talked about a paper looking at how the degree to which we take risks may fluctuate more than we think...

Helen - I've been looking at a paper asking why it is that sometimes we make risky decisions whereas sometimes we might be more risk averse. And this study suggests that perhaps we're not quite as stable as we might think we are. And while it might be true that we might have some risk taking traits or some risk averse traits, this study does show that actually our behaviour is quite erratic, more erratic than we might like to believe about ourselves.

So the background of this is we tend to look at risk taking at a population level, and that some people are prone to taking risks. In particular younger people are known to be more prone to taking risks than older people by about 5 percent. This study is run on the basis that we are almost slaves to the brain chemical dopamine so dopamine - a feel good chemical in your brain. And generally people whose brains are saturated with dopamine will take more risks. This is really widely established and in general a big head of dopamine feels good and people can tend to return for another rush, it can lead to a lot of addictive behaviours.

In this study the researchers used fMRI which can show us different levels of activity in the brain over a period of time and they focused on the dopaminurgic midbrain. This is part of your brain that's really centrally involved in decision making. What was really neat about this study was that they tied the presentation of stimulus to your brain responses. So they looked at the dopaminurgic midbrain and if you were just in your resting state, had very low activity there, this would trigger the presentation of a stimulus.

Katie -  And the stimulus is doing something risky?

Helen - It is indeed. So the interesting part is they tied the presentation of a stimulus to when you in your resting state had low or high activity in this region. And when that happened, let's say you had low resting activity in this region, you would then be presented with an interesting potentially risky choice.

So you would be asked to choose on a gambling task as to whether you wanted to go for a low amount of money, a safe option so say three pounds, or whether you wanted to make a choice, a gamble, where you could get more money than that so potentially six or nine pounds or zero.

And they found that if in your dopaminurgic midbrain you had very low activity, a low resting state, and you're suddenly presented with this gambling choice, there's quite a spike in your dopamine activity. And that spike in dopamine leads to you actually taking a more risky decision. So within the same session, if in your resting state you had a high activity in this brain area and you're presented with a risky choice, there wasn't quite the same dopamine spike and you tended to make a safer choice.

Katie - Ah OK. But this is within one person, right? So does that mean on any given day you can have higher or lower levels of dopamine in your brain?

Helen - It absolutely does and this is what was quite surprising about this study. It was really neat just within one fMRI session people were making quite different gambling choices, just on things we have no control over, so background fluctuations in resting state activity in this part of your brain.

Katie - Here’s me thinking that I'm a very habitually cautious person, maybe that is not true?

Helen - Well you may be a habitually cautious person, but I think you might not be as consistent within yourself as you might think. We need to remember that risk taking activity isn't just a generic negative. There can be real reasons for us taking risks! So if we want to be ambitious and make progress, whether that's in our work life, or our romantic life, or any aspect of our life, we're gonna need to have these fluctuations, we're gonna need to sometimes push ourselves and take a few more risks.

And this mechanism might be quite helpful for this and indeed the authors of this study suggest these background fluctuations might make us a bit more unpredictable and even might make us better able to adapt to different situations. So there could be good use in these background fluctuations.

I think what this does point to is we can be a bit more self-aware. So it does suggest that some decisions we're making or the way you make decisions can be somewhat out of our control, our behaviour can be somewhat erratic. It doesn't give us much hope, does it, for ourselves!

But what it does suggest is that things that I'm quite interested in, like the development of driverless cars, could be really really good because if these background fluctuations are going to affect particularly risk taking behaviour, let's take that out of the equation altogether and make more sensible choices.

Duncan - It’s interesting that there are various conditions where risk taking can become pathological. So for instance people who become addicted to dangerous narcotics and that kind of thing. And there's been a lot of interest in the role that the dopamine system plays. Are there underlying genetic differences in our dopamine systems, such that for instance if some people's dopamine systems are just much more erratic, then that means that there might be periods where they're exceptionally prone to taking big risks like, “inject this substance”?

Katie - Oh I see. So there's fluctuation in everyone but there could be more fluctuation in some people.

Duncan - Yeah. So there is some genetic susceptibility for certain types of substance abuse addiction for example. And it's interesting that there are various medications on the market to try and mimic dopamine action so for instance something like Parkinson's where because of the loss of dopamine receptors, the medication tries to boost the amount of dopamine.

And what you'd find is exactly what you'd expect from what you've said is that, that obviously helps with some symptoms, but they start to struggle with any tasks that require them to gauge rewards and make choices about rewards i.e. make risks. Because their levels of dopamine are just high the whole time

Duncan looked at a stimulating paper on transcranial magnetic stimulation...

Duncan - So this is using transcranial magnetic stimulation. It's also very interesting paper and it's looking at anhedonia, inability to find joy and enjoyment in the things that we do.

Katie -  Are you talking about depression?

Duncan -  It is a very common symptom. About 70 percent of those with major depressive disorder will experience this symptom. It's regarded as a very stubborn symptom for treatment options and people who score particularly highly on this symptom tend to be those who are most resistant to the current forms of treatment.

So in this study they recruited 19 subjects who all had major depressive disorder and particular problems with anhedonia. They rated them on an anhedonia scale. And they also performed a task which required them to look at faces that convey different types of emotion, and those faces are manipulated to make it really tricky to judge the differences, e.g. how happy is this person?

Then the subjects are divided into two groups and both of them receive a type of stimulation applied to a part of the frontal lobe called the dorsal lateral prefrontal cortex, which people have previously thought might be important in the symptom of anhedonia.

Katie - What does it mean to stimulate this bit of the brain? What are you doing to somebody?

Duncan - So you will remember from GCSE or equivalent physics that wherever you get an electrical current running in a particular direction you will also get a magnetic field running counter to it. It’s called the right hand rule.

Katie - This does bring back memories of my physics lessons!

Duncan - The same is true of your brain. So when the neurons fire, the axons in different layers of the brain are really well aligned and that can create an electrical current that generates magnetic field, and we can measure that outside the brain. And the same thing goes in reverse if we can induce a big magnetic field just outside your head, then we can kind of fire the electrical activity within those neurons.

And so what TMS does, it's two coils, essentially a big loop of iron that has got lots of wire wrapped around it. And then at the flick of a switch a very large electrical current is put through the wire to create an electromagnet. And then when that's applied to the outside of your head, it generates a big enough magnetic field on the outside to get the neurons firing on the inside.

Katie - So how does this relate to anhedonia then?

Duncan - Good question. So what they did essentially was to apply repetitive transcranial magnetic stimulation to this part of the brain called the dorsal lateral prefrontal cortex. And they did it for 20 sessions and in each session a person would receive 3000 bursts of TMS and this at 10 hertz at 10 per second.

And then people come back into the lab, they repeat the emotional faces task, and they repeat the anhedonia questionnaire. Now half of the group unbeknownst to them they are not receiving the real stimulation. And what they find is that people who have had the real deal active stimulation do indeed show better sensitivity on that faces task, and the degree of change on the faces task is predictive of the degree of improvement that they show on the anhedonia questionnaire.

Katie - So what's going on to make this relationship?

Duncan - Well one popular idea is that there are various parts of the brain which are something called the limbic system so areas like the amygdala, that are really important in processing emotional content. But that that can be regulated by other areas like the dorsal lateral prefrontal cortex.

And what might be going wrong in subjects who experience anhedonia, is they’re not able to regulate this lower level brain area. And so one possibility is that by stimulating the dorsal lateral prefrontal cortex it’s then better able to regulate the amygdala and thus you're better able to experience the emotional content of the faces and experience less anhedonia.

This kind of thing is seen as a potential alternative route to treatment. So we know that the current best quality NHS gold standard treatment, which is usually cognitive behavioural therapy with some kind of pharmaceutical agent, is effective fir 50 to 60 per cent of individuals. And so treatments like this are seen as a possibility.

But there are some real questions surrounding it. Number one its feasibility, so can we really scale this up? Secondly how long does it last? Would the person keep having to come back in every couple of months for another set of sessions? Can you deliver it to people of all ages? Could you give this to an adolescent for example who is particularly prone to depression?

Katie - Do we know anything about what happens to the brain of a younger person who you're putting in this situation?

Duncan - Not really. There've been some long term follow up to this kind of stimulation done with adults, but there's not really been any work done with kids because we don't really know the effect that it might have on the developing brain.

Katie - I'm assuming that this is a safe technology that doesn't seem to cause brain regions any harm?

Duncan - Yeah so there's no evidence whatsoever that this does any harm to the brain.

These studies are relatively high risk to run so they tend to be run on a small scale. So really to see whether it's genuinely effective you'd need to scale it up.

Katie - Do you think looking at people's faces, where the emotion is difficult to read, is a good measure of anhedonia? It sounds like something that could be quite a difficult task even if you don't have anhedonia.

Duncan - There might be lots of reasons why you might be bad at that task. A general challenge is finding tasks that sit between the kind of basic intervention you've done, whether it be a drug, a therapy, stimulation technique, and the ultimate outcome which is symptoms in the real world. So in the middle of that we try and think of tasks that we think might be sensitive to the underlying symptoms. But ultimately they're always quite a long way from the real world. Sitting in a lab and looking at faces static on the screen as they flash up in 2D isn't really much like real life but at the minute it's kind of the closest that we can get in the lab setting.

COFFEE

14:08 - How do we move?

How are you able to pick up that coffee cup?

How do we move?
Isabelle Cochrane, trainee doctor

What's actually going on in the brain and body, to allow us to move, like in reaching for a coffee? Trainee doctor Isabelle Cochrane has been brewing up an answer...

Movements are generated when a  type of nerve, called a motor neurone, sends a chemical signal directly to a muscle, causing it to contract. This can occur in response to a sensory stimulus from the environment: contact with a hot surface, or a stinging nettle, for instance, causes a rapid withdrawal reflex!. Movements are also voluntary such as walking, or using tools, to do things like typing, or throwing a ball..

The parts of the nervous system that generate movements are collectively called the motor system. Over millennia, these have evolved to operate automatically. This means that most of our movements are not under direct conscious control: even though the decision to carry out a particular movement might be conscious, we do not have to think consciously about the sequence of nerve signals, muscle contractions, and joint movements that are going to be needed to carry out an action successfully. Instead, these calculations are carried out at various levels in the motor system.

So let’s start by looking at withdrawal reflexes.

These occur when a painful or unpleasant stimulus is experienced, for instance touching a piping hot oven dish. The result of this stimulus will be something we have all experienced: an almost instantaneous removal of the affected digit from the offending item. When researchers first studied this historically they realised that this reaction occurs far too rapidly for the movement commands to be going via the brain. Instead, sensory neurones that detect painful stimuli are linked, via short spinal nerve cells called interneurones, straight to the motor neurones responsible for withdrawing a limb from the noxious stimulus. In other words, the machinery of the spinal cord is sufficient to generate one of the less complex goal-directed movements. Of course, we know the story is not so simple: for instance, no matter how painful it is, we can resist dropping our favourite mug full of steaming coffee. Many of our spinal reflexes are ultimately still under the control of the brain, which can refuse permission for a particular action to take place.

So is the spinal cord able to generate movement other than reflexes? In  vertebrates, it would appear that the answer is generally “yes” - the spine contains networks of neurones known as ‘central pattern generators’. These fire rhythmically to produce stereotyped movements, such as swimming, scratching and walking. However, the story is less clear cut in man and scientists aren’t sure whether there are central pattern generators in the adult human spinal cord, or whether these circuits are located elsewhere in the nervous system, such as the brain.

The part of the brain that is responsible for producing movement commands is called the primary motor cortex; this is  a strip of brain tissue which sits roughly beneath where your headphones rest on your head. The primary motor cortex is organized like a map of the body, with different regions of the cortex responsible for the muscles of a particular part of the body. This part of the brain – and the bundles of nerve fibres that flow from it - are commonly affected by strokes, which is why one of the most prominent symptoms of a stroke is paralysis of the arm, leg or face - and based on which of these structures is paralysed, one can predict quite accurately which part of the motor cortex has been affected.

 

The nerve fibres that flow away from the motor cortex form two bundles that run down the front of the spinal cord and are called the corticospinal tracts; the nerves exit these bundles at the right locations along the spinal cord to connect to and activate target motor neurones and intermediate “interneurones” that control muscles. 

So how does the motor cortex actually make a movement happen? At a simple level, a nerve cell in the motor cortex becomes active and fires a barrage of impulses along its fibre down the corticospinal tract. These impulses are transmitted to and activate a select group of motorneurones and interneurones in the part of the spinal cord that controls the relevant part of the body you want to move. When the motorneurones fire up, the muscles they activate contract, and you move. 

In reality it is, of course, more complex than this. The motor cortex tends to be organised in terms of ‘motor synergies’. This means that the brain contains libraries of various useful movement combinations - for example, activating the muscles that stretch the elbow and the muscles that stretch the wrist simultaneously, in order to reach out and grab an object. Sensory feedback during a movement can help to modify these synergies, both at the time of the action, in order to refine the movement, but also in the future, enabling a learning process by which this ‘library’ can be expanded.

You might wonder, though, what controls the motor cortex? That role – in planning and refining movements before they happen falls to structures that sit just in front of the motor cortex, just behind your forehead. These are the supplementary motor area and pre-motor cortex. They are richly connected with the front parts of the brain that are involved in decision-making, as well as with other brain structures such as the cerebellum, which helps with the coordination of movement and in learning new movements, and the basal ganglia, which are involved in  delivering the “go signal” that kicks off a movement in the first place.

So next time you reach for your cup of coffee, spare a thought also for the millions of neurons buzzing away in your motor cortex, cerebellum and spinal cord to ensure that the coffee ends up where it should and when it should!

OLDER-PEOPLE

20:14 - Controlling movement

How might control over our movements change as we age?

Controlling movement
Ann-Maree Vallence, Murdoch University

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.

WALKING

28:01 - We're so in sync

How does walking in synchrony with someone impact your relationship?

We're so in sync
Lynden Miles, UWA

How does walking in synchrony with someone impact your relationship? Katie Haylor put this to Lynden Miles from the University of Western Australia... 

Lynden - So the idea of synchrony is that we move at the same time with the same movements as somebody else, with their interaction partners.

Katie - So is this when say I'm walking down the street with a friend or a relative or maybe someone I don't know, I strike up a conversation and I find myself hitting the pavement with my feet actually at the same time as them?

Lynden - That's exactly right, that's what we'd call in phase synchrony and your footsteps tend to coordinate in the same way. Almost as if you're you're marching together with them. But often it's just happened spontaneously and unintentionally and you don't really even notice it's going on.

A lot of the time in particular the things we do for fun like singing and dancing and moving we'll practice really quite a lot that synchronizing our movements. And we tend to get the same sort of positive social benefits that we enjoy, the moving together with other people. We pay lots of attention to it, we get a lot of social feedback when we do the same thing as somebody else, tends to be that regardless of whether it's spontaneous or intentional we still enjoy the benefits of synchronous movement.

Katie - I remember being a kid and being stuck in the back of the car on a long car journey and noticing that when you're in a traffic jam, car indicators are sometimes in sync and sometimes out of sync. And it's really annoying when they're out of sync! But I also noticed that I used to do this with my friends. I would purposely try and be in step with them. Does that have any relevance here if we’re talking about social relationships?

Lynden - That's really funny because I had the same problem as a kid, I got quite annoyed when the indicators were out of sync with each other. That's what we'd call incidental synchrony. There's no real coupling between the car indicators, they come and go or they just kind of coincidentally synchronize. What's really important with people is that we have some sort of coupling or some sort of joining to them. Often it's just paying attention to them, seeing their movements and their movements influence ours and vice versa, our movements influence theirs. Until we come to a kind of a common movement frequency and we do the same thing at the same time.

Katie - So you've got mathematical with this relationship right? Can you tell us a bit about how that works?

Lynden - What we really do is just borrow some models from physics. They essentially say that as long as two things are moving at roughly the same frequency, so the same speed as each other, and somehow they're joined. So they’re coupled in some way. Often visually with people or we could hear their footsteps. Then the models predict that we’ll coordinate in either in phase coordination, so we're stepping at exactly the same time as the other person or an anti phase coordination so that for instance when we're stepping with our left leg, they'll be stepping with their right leg. And the models predict this across all sorts of systems, from metronome synchronizing, to fireflies flashing off and on, to people coordinating their footsteps.

Katie - So what does that have to do with our social relationships then?

Lynden - Turns out that when we synchronize in this way, because there's an infinite number of ways we could coordinate our behaviour, people tend to coordinate in exactly the same ways as predicted by the physics.

And that seems to be a sign of positive and effective social relationships. So we like each other more when we synchronize, we remember each other more, we get a wee boost in self-esteem.

Katie - And how strong is this relationship between socializing and being in step, literally?

Lynden - Well I guess there's a whole bunch of different things and different influences of how well we get along with each other. We almost always use strangers coming into the lab and we have simple synchrony exercises or ways of inducing synchrony with our participants. And even with strangers they tend to form a relatively tight and almost instant bond.

They change the way they think about each other. They like each other more. They remember each other more. Typically we remember more about ourselves than we remember about other people, unless they are significant others. But after about a two or three minute period of in phase synchrony, we start to remember more about our interaction partners, as if we have formed a long term relationship with them. Our cognition and our social cognition changes in the same way they would when we've had a long term and substantial relationship with someone. They engage in more in-depth conversations and that sort of thing. And it's an interesting relationship because it kind of goes both ways. The more we synchronize with people, the more we like them, and the more we like people, the more we synchronize with them.

Katie - How have you discovered that the social cognition has changed? Are you sticking people in a scanner or are you asking them about it?

Lynden - So we do simple things like we give them a task whether moving synchronously or  asynchronously, and over headphones we play them some words and ask them to say those words out loud. They believe that these words are just distraction words and so they are saying some words out loud, they are hearing an interaction partner saying some words out loud. And after two or three minutes of synchrony, then we stop them and we give them what we call a surprise recall test.

And after they've been synchronous, they remember just as many words that they've said as their partner said. But after an asynchronous interaction or they don't have movement involved in their interaction, they seem to remember more about themselves than the other person. This is what's called the self reference effect. It's really common effect. I remember more about myself than other people, except when those other people are significant others. And we can kind of replicate that long term relationship with a two to three minute period of synchrony.

We also remember what these people look like better. So we take a photograph of our participants and then we morph their faces, with a whole lot of other faces. So we end up seeing people who look similar to each other. And participants who have synchronized with an experimenter tend to better pick who the experimenter is out of a bunch of faces, much better than people who haven't synchronized.

Katie - Is there a breakdown of particular social relationships? I'm wondering if this might be quite a good dating technique, walking in step with people?

Lynden - I guess it should reinforce that initial liking between each other. We have a little bit of data that we haven't published yet that says friends probably don't coordinate or synchronize to the same extent to strangers. And we're wondering whether this is because we have this deep desire or need to belong and need to affiliate with people and need to have smooth social interactions. So we deploy coordination as a mechanism to overcome any social awkwardness and kind of close the gap between people, particularly on their initial meetings.

Katie - I'm really interested to know how long we've known about this because people have been using this technique for hundreds, thousands of years. Getting armies to march together and the social impact that must have. I mean that's got to have gone back centuries, right?

Lynden - That's right. I think we've been implicitly understanding that something about doing the same thing at the same time as each other, there's a really strong form of social bonding. There’s some ideas that this might have a deep evolutionary history and this is one of the first ways we were able to form groups and coalitions together by perhaps singing, or dancing, or drumming around the campfire. And as you say the military have  used this for a very long time. The really interesting thing that the military still use a lot of marching drills. They don't march into battle anymore, perhaps it  isn't so wise with the invention of the machine gun, and things along those lines. But military drills still involve a lot of marching in time and behaving in the same way as somebody else, and the idea there is that it provides a cohesive unit that provides you know a sense of belonging and a sense of camaraderie with your fellow people.

Katie - Can you tell us a bit about why you think this relationship occurs? What's the mechanism that you think you're getting at here?

Lynden - Probably a multilayered mechanism. I think doing the same thing at the same time has a lot of reinforcing properties. So we're sharing a common interest, we're sharing a common fate. It also means that we're paying attention to each other. Part of the way that we synchronize is by having an attentional coupling. By knowing what other people are doing, and seeing what other people are doing and this is also a sign of a good interaction or a good relationship. We pay lots of attention to the people we like and so it's mutually reinforcing in this way.

A wee bit lower in the system in the brain level, we get common patterns of brain activity when people are doing stuff. So again they’re sharing experiences, it tends to be again mutually reinforcing. There's some evidence that there's some hormonal changes, we may have endorphin release, a pleasure hormone, when we synchronize with other people. And so I think there's a lot of levels which all seem to reinforce the same idea that doing the same thing as their interaction partners provides a platform or a basis for an effective and pleasant social interaction.

Katie - So actually me skipping down the road with my friends, linking arms and trying to step at the same time as each other seems to make quite a lot of sense!

Lynden - Absolutely, I think it's one nice way of building up some enduring bonds.

Katie - This relationship, if it is quite a strong one, could this be used as an indicator of when for instance someone might be having social difficulties? 

Lynden - Yeah absolutely. Some really recent work we've been doing is looking at social anxiety, so people who experience symptoms of social anxiety tend to have accompanying social difficulties. And what we've been showing is that the way people who have higher levels of social anxiety coordinate with other people has less stability. So the coordination is less good, it's less stable, it doesn't happen in quite the same way.
And we are starting to wonder whether this has a wee bit of a feedback loop. So if symptoms of social anxiety are producing less effective coordination, perhaps that then heightens the sensation or the experience of social anxiety, which again in turn lessens the quality of coordination. So we’re starting to do some work that looks at whether symptoms of mental health, whether deficits or disruptions to coordination can act as a marker or a signature of instability in mental health.

Katie - But it's not just stepping is it? We've been talking a lot about walking here but I’m just thinking, I played the cello as a kid. There must be so much about synchrony and asynchrony when you're making music together for instance.

Lynden - Absolutely and I think music gives people a common source or a common rhythm that they can you know use to both synchronize together really easily. But I think also other movements like posture and postural sway and just all of the little nonverbal behaviours and movements that we have, probably contribute to the same idea.

Similar emotional experiences, we mimic and synchronize each other's facial expressions and emotions as well, I think then feeds into the same idea that if we synchronize our behaviours then that can lead to a shared and common understanding.

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