Control of Movement And Action – Technically Challenging Conceptual Requirements And Exquisite Control Mechanisms Underpin Even Lifting Up Your Coffee Cup

During the Christmas break we stayed in Durban with my great old friend James Adrain, and each morning I would as usual wake around 5.00 am and make a cup of coffee and sit outside in his beautiful garden and reflect on life and its meaning before the rest of the team awoke and we set off on our daily morning bike-ride. One morning I accidentally bumped my empty coffee mug, and as it headed to the floor, my hand involuntarily reached out and grabbed it, saving it just before it hit the ground. During the holiday I also enjoyed watching a bit of sport on the TV in the afternoons to relax after the day’s festivities, and once briefly saw highlights of the World Darts Championship, which was on the go, and was struck by how the folk competing seemed with such ease, and with apparent similar arm movements when throwing each dart, to be able to hit almost exactly what they were aiming for, usually the triple twenty. When I got back home, I picked up from Twitter a fascinating article on movement control posted by one of Sport Sciences most pre-eminent biomechanics researchers, Dr Paul Glazier, written by a group of movement control scientists including Professor Mark Latash, who I regard as one of the foremost innovative thinkers in the field of the last few decades. All of these got me thinking about movement control, and what must be exquisite control mechanisms in the brain and body which allowed me to in an instant plan and enact a movement strategy which allowed me to grab the falling mug before it hit the ground, and allowed the Darts Championship competitors to guide their darts, using their arm muscles, with such accuracy to such a small target a fair distance away from them.

Due to the work over the last few centuries of a number of great movement control researchers, neurophysiologists, neuroscientists, biomechanists and anatomists, we know a fair bit about the anatomical structures which regulate movement in the different muscles of the body. In the brain, the motor cortex is the area where command outflow to the different muscles is directly activated, and one of the highlights of my research career was when I first used transcranial magnetic stimulation, working with my great friend and colleague Dr Bernhard Voller, where we able to make muscles in the arms and leg twitch by ‘firing’ magnetic impulses into the motor cortex region of the brain by holding an electromagnetic device over the scalp above this brain region. The ‘commands for action’ from the motor cortex travel to the individual muscles via motor nerves, using electrical impulses in which the command ‘code’ is supplied to the muscle by trains of impulses of varying frequency and duration. At the level of the individual muscles, the electrical impulses induce a series of biochemical events in and around the individual muscle fibres which cause them to contract in an ‘all or none’ way, and with the correct requested amount of force output from the muscle fibre which has been ‘ordered’ by the motor cortex in response to behavioural requirements initiated in brain areas ‘upstream’ from the motor cortex, such as one’s eyes picking up a falling cup and ‘ordering’ reactive motor commands to catch the cup. So while even though the pathway structures from the brain to the muscle fibres are more complex than I have described here – there are a whole host of ‘ancient’ motor pathways from ‘lower’ brainstem areas of the brain which also travel to the muscle or synapse with the outgoing motor pathways, whose functions appear to be redundant to the main motor pathways and may still exist as a relic from the days before our cortical ‘higher’ brain structures developed – we do know a fair bit about the individual motor control pathways, and how they structurally operate and how nerve impulses pass from the brain to the muscles of the body.

However, like everything in life, things are more complex than what is described above, as even a simple action like reaching for a cup, or throwing a dart, requires numerous different muscles to fire either synchronously and / or synergistically, and indeed just about every muscle in the body has to alter its firing pattern to allow the body to move, the arm to stretch out, the legs to stabilize the moving body, and the trunk to sway towards the falling cup in order to catch it. Furthermore, each muscle itself has thousands of different muscle fibres, all of which need to be controlled by an organized ‘pattern’ of firing to even the single whole muscle. This means that there needs to be a coordinated pattern of movement of a number of different muscles and the muscle fibres in each of them, and we still have no idea how the ‘plan’ or ‘map’ for each of these complex pattern of movement occurs, where it is stored in the brain (as what must be a complex algorithm of both spatial and temporal characteristics to recruit not only the correct muscles, but also the correct sequence of their firing from a timing perspective to allow co-ordinated movement), and how a specific plan is ‘chosen’ by the brain as the correct one from what must be thousands of other complex movement plans. To make things even more challenging, it has been shown that each time one performs a repetitive movement, such as throwing a dart, different synergies of muscles and arm movement actions are used each time one throws the dart, even if to the ‘naked’ eye it appears that the movement of the arm and fingers of the individual throwing the dart seems identical each time it is thrown.

Perhaps the scientist that has made the most progress in solving these hugely complex and still not well understood control process has been Nikolai Bernstein, a Russian scientist working out of Moscow between the 1920’s and 1960’s, and whose work was not well known outside of Russia because of the ‘Iron Curtain’ (and perhaps Western scientific arrogance) until a few decades ago, when research folk like Mark Latash (who I regard as the modern day equivalent of Bernstein both intellectually and academically) translated his work into English and published it as books and monographs. Bernstein was instructed in the 1920’s to study movement during manual labour in order to enhance worker productivity under the instruction of the communist leaders of Russia during that notorious epoch of state control of all aspects of life. Using cyclographic techniques (a type of cinematography) he filmed workers performing manual tasks such as hitting nails with hammers or using chisels, and came to two astonishing conclusions / developed two movement control theories which are astonishingly brilliant (actually he developed quite a few more than the two described here), and if he was alive and living in a Western country these would or should have surely lead to him getting a Nobel prize for his work. The first thing he realized was that all motor activity is based on ‘modelling of the future’. In other words, each significant motor act is a solution (or attempt at one) of a specific problem which needs physical action, whether hitting a nail with a hammer, or throwing a dart at a specific area of a dartboard, or catching a falling coffee cup. The act which is required, which in effect is the mechanism through which an organism is trying to achieve some behavioural requirement, is something which is not yet, but is ‘due to be brought about’. Bernstein suggested that the problem of motor control and action therefore is that all movement is the reflection or model of future requirements (somehow coded in the brain), and a vitally useful or significant action cannot either be programmed or accomplished if the brain has not created pre-requisite directives in the forms of ‘maps’ of the future requirements which are ‘lodged’ somewhere in the brain. So all movement is in response to ‘intent’, and for each ‘intent’ a map of motor movements which would solve this ‘intent’ is required, a concept which is hard enough to get one’s mind around understanding, let alone working out how the brain achieves this or how these ‘maps’ are stored and chosen.

The second of Bernstein’s great observations was what is known as motor redundancy (Mark Latash has recently suggested that redundancy is the wrong word, and it should have been known as motor abundancy), or the ‘inverse dynamics problem’ of movement. When looking at the movement of the workers hitting a nail with a hammer, he noticed that despite them always hitting the nail successfully, the trajectory of the hammer through the air was always different, despite the final outcome always being similar. He realized that each time the hammer was used, a different combination of arm motion ‘patterns’ was used to get the hammer from its initial start place to when it hit the nail. Further work showed that each different muscle in the arm was activated differently each time the hammer was guided through the air to the nail, and each joint moved differently for each hammer movement too. This was quite a mind-boggling observation, as it meant that each time the brain ‘instructed’ the muscles to fire in order to control the movement of the hammer, it chose a different ‘pattern’ or ‘map’ of coordinative muscle activation of the different muscles and joints in the arm holding the hammer for each hammer strike of the nail, and that for each planned movement therefore, thousands of different ‘patterns’ or ‘maps’ of coordinated muscle movement must be stored, or at least available to the brain, and a different one appears to be chosen each time the same repetitive action is performed. Bernstein therefore realized that there is a redundancy, or abundancy, of ‘choice’ of movement strategies available to the brain for each movement, let alone complex movement involving multiple body parts or limbs. From an intelligent control systems concept, this is difficult to get one’s head around, and how the ‘choice’ of ‘maps’ is made each time a person performs a movement is still a complete mystery to movement control researchers.

Interestingly, one would think that with training, one would reach a situation where there would be less motor variability, and a more uniform pattern of movement when performing a specific task. But, in contrast, the opposite appears to occur, and the variability of individual muscle and joint actions in each repetitive movement appears to maintain or even increase this variability with training, perhaps as a fatigue regulating mechanism to prevent the possibility of injury occurring from potentially over-using a preferentially recruited single muscle or muscle group. Furthermore, the opposite appears to happen after injury or illness, and after for example one suffers a stroke or a limb ligament or muscle tear, the pattern of movements ‘chosen’ by the brain, or available to be chosen, appears to be reduced, and similar movement patterns occur during repetitive muscle movement after such an injury, which would also be counter-intuitive in many ways, and is perhaps related to some loss of ‘choice’ function associated with injury or brain damage, rather than damage to the muscles per se, though more work is needed to understand this conceptually, let alone functionally.

So, therefore, the simple actions which make up most of our daily life, appear to be underpinned by movement control mechanisms of the most astonishing complexity, which we do not understand well (and I have not even mentioned the also complex afferent sensory components of the movement control process which adjust / correct non-ballistic movement). My reaction to the cup falling and me catching it was firstly a sense of pleasure that despite my advancing age and associated physical deterioration I still ‘had’ the capacity to respond in an instant and that perhaps the old physical ‘vehicle’ – namely my body – through which all my drives and dreams are operationalized / effected (as Freud nicely put it) still works relatively okay, at least when a ‘crisis’ occurs such as the cup falling. Secondly I felt the awe I have felt at many different times in my career as a systems control researcher at what a brilliant ‘instrument’ our brains and bodies as a combination are, and whatever or whoever ‘created’ us in this way made something special. The level of exquisite control pathways, the capacity for and of redundancy available to us for each movement, the intellectual capacity from just a movement control perspective our brain possesses (before we start talking of even more complex phenomena such as memory storage, emotional qualia, and the mechanisms underpinning conscious perception) are staggering to behold and be aware of. Equally, when one sees each darts player, or any athlete performing their task so well for our enjoyment and their success (whether darts players can be called ‘athletes’ is for another discussion perhaps), it is astonishing that all their practice has made their movement patterns potentially more rather than less variable, and that this variability, rather than creating ‘malfunction’, creates movement success and optimizes task outcome capacity and performance.

It is in those moments as I had when sitting in a beautiful garden in Durban in the early morning of a holiday period, reflecting on one’s success in catching a coffee cup, that creates a sense of wonder of the life we have and live, and what a thing of wonder our body is, with its many still mystical, complex, mostly concealed control processes and pathways regulating even our simple movements and daily tasks. In each movement we perform are concealed a prior need or desire, potentially countless maps of prospective plans for it, and millions of ways it can be actualized, from which our brain chooses one specific mechanism and process. There is surely magic in life not just all around but in us too, that us scientist folk battle so hard to try and understand, but which are to date still impenetrable in all their brilliance and beauty. So with a sigh, I stood up from the table, said goodbye to the beautiful garden and great friends in Durban, and the relaxing holidays, and returned to the laboratory at the start of the year to try and work it all out again, yet knowing that probably I will be back in the same place next year, reflecting on the same mysteries, with the same awe of what has been created in us, and surely still will no further to understanding, and will still be pondering, how to work it all out – though next year I will be sure to be a bit more careful where I place my finished coffee cup!

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About Alan (Zig) St Clair Gibson

Professor Alan (Zig) St Clair Gibson MBChB PhD MD - Deputy Dean (Research), Faculty of Science and Health, University of Essex, Colchester, United Kingdom View all posts by Alan (Zig) St Clair Gibson

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