Welcome to part two of _On the brain, a Conversation series by people whose job it is to know as much as there is to know about the body’s most complex organ. Here, Malcolm Horne, deputy director of the Florey Neuroscience Institutes, explores the brain’s role in our capacity to move and, through our understanding of this, the way we might treat brain disorders._
The 2003 Rugby World Cup final between Australia and England was a tense match with scores level through each team scoring penalty goals.
Under the scrutiny of a 100,000 strong crowd and the millions around the world watching on TV, the players had to step up and strike the kick accurately to keep their team in the game.
Kicking (well) is a highly learned and practiced skill but one that easily disappears under cognitive pressure.
It also exemplifies the way human movement differs from that of other animals by showing the capacity of humans to learn and modify their movement to achieve specific outcomes.
The capacity to move so as to capture food or engage in reproduction was a very early step in human evolutionary history. Traces of this ancient history are reflected in the structure and workings of the human spinal cord, which controls movement in the same way as almost all other animals including reptiles.
With time, the mammalian brain has evolved extra neural equipment, layered over these basic spinal reflex paths, to achieve more complex control of the spinal systems.
These neural systems coordinate the four limbs and trunk with information from the eyes, ears and balance system: this function is well exemplified in the silky movements of the cat.
Our understanding of how these systems work has advanced to the degree that active research is directed at tapping into and recording from these brain structures to control prosthesis for aiding people with brain injury in standing, walking and grasping objects.
Although cats and other animals move gracefully and are perfectly adapted to survive and function in their natural habitat, humans more than any other animal can learn or modify movements, adapting them to carry out new tasks.
No other animal has the capacity to learn the piano, to play tennis, putt in golf, drive a car or kick goals in rugby.
This capacity results from frontal lobes (see below) forming a further layer of control of the older movement systems. The frontal lobes lie behind the frontal bones and above the eyes, and have expanded greatly in humans.
Their growth is a major reason for the increased brain size of homo sapiens and importantly, for their capacity to reason.
Understanding how conscious, goal-directed behavior drives skilled movement is a major goal. The issues can be exemplified by reflecting on learning to drive.
The young driver initially devotes all of his or her attention on coordinating gears, clutch, steering wheel, brakes and accelerator, with almost no capacity for attending to pedestrians or other traffic.
Slowly the basic skills are learned and are carried out almost effortlessly and, in effect, subconsciously, so attention can be directed at negotiating traffic and talking to passengers. This process is a fundamental action of the frontal lobes.
By using a mechanism called “working memory” the frontal lobes can attend to a handful of items: one example might be remembering a telephone number for long enough to dial it.
Depending on the complexity of the task, most people can hold five or so items in their attention.
When learning to drive, working memory/attention is fully engaged in coordinating the mechanics of driving. At the same time, the frontal lobes, including a structure called the basal ganglia, is busy “learning” the components of driving, such as changing gears.
These components are referred to as “chunks” and, when used in a particular sequence, they can produce a more complex goal-directed movement.
Importantly, with learning, attention is no longer directed at producing the chunk of movement but in attending to the goal of the complex movement.
A single note of music can be produced on the piano, even by a novice, and producing them in order, and with suitable timing, produces a tune. Learning to play the piano means the chunks of movement required to make sequences of notes is done automatically so that attention can be directed at making music rather than the mechanics of playing the piano.
Learning to drive entails turning the motor tasks into skilled chunks so that attention can be directed at traffic and safety.
Paradoxically, turning attention back on to performing the chunks can degrade their production. Kicking for goal in rugby or putting in golf is best achieved when the frontal lobes produce the movements automatically.
One of the aims of sports psychology is to ensure that, even though the world is watching, the movements are performed automatically.
Understanding how these skilled, goal-directed movements are made will influence the way people are taught and trained to develop complex motor skills.
Diseases of movement
This knowledge is vitally important to diseases of movement. Parkinson’s disease affects the brain regions and chemicals required to produce skilled movements. As a result, goal-directed movement is lost.
On the other hand, disorders such as Tourette’s syndrome may reflect the irrelevant, inappropriate and unwanted production of fragments of movements called tics.
It’s becoming apparent that closely related regions in the frontal lobes use a similar process to control many forms of learned and skilled behaviour, including language acquisition, behavioural habits and even falling in love.
Thus discovering how chunks of movement are learned and then used to make goal-directed behaviours might not only help in elite sport, but in many other facets of human behaviour.
Impulse control
Struggling to speak “schoolboy” German in Berlin is analogous to learning to drive: we are still struggling with the mechanics of language production rather than using it for the goal of communication.
Fluent speakers effortlessly respond to questions and comments and, while some of these responses are thoughtful and considered, many are more habitual and stereotyped, reflecting current language fashions.
Many morning greeting rituals are a form of word tennis with two or three brief exchanges about the weather and how we are all well, thank you.
The impulsive response can result in that experience of having said something and then wishing the words back could be taken back.
The reflexive or impulsive production of movement, whether it be language, sport or music, is efficient and produces highly levels of motor performance.
But it also leads to impulsive behaviour that’s not always appropriate.
One key role of the frontal lobes is to arbitrate between the times when the response to the impulse should be suppressed and when it can be allowed.
The effectiveness of this regulation may be what results in a number of impulsive behaviours or disorders.
The brain is a sophisticated motor that, when trained, will produce sublime musicians and great goal-kickers – but, as with any sophisticated instrument, minor changes in function can have serious consequences.
This is the second part of our series On the brain. To read the other instalments, follow the links below:
Part One: Picking your brains: what’s going on inside your head?
Part Three: Brain’s addiction: what makes heavy drug users different?
Part Four: Brain’s addiction: is shooting up a disease or a choice?