MOTOR CONTROL

1. MOTOR CONTROL

2. Learning objectives • understand the role of the brain during movement • understand the nature and role of proprioception • understand how Information Processing Theory explains how we move • understand how Dynamical Systems Theory explains how we move • understand some of the basic theories of motor development • understand how development affects motor control

3. PRE-MOTOR CORTEX SENSORY CORTEX BASAL GANGLIA CEREBELLUM LONG LOOP BRAINSTEM SPINAL CORD SHORT LOOP MUSCLES DIAGRAMMATIC EXPLANATION OF TOP-DOWN CONTROL OF MOVEMENT Black arrows represent feedforward Red arrows represent feedback

4. ANTERIOR CINGULATE CORTEX THALAMUS PRIMARY MOTOR CORTEX SMA SOMATOSENSORY CORTEX PMC DLPFC SOMATOSENSORY ASSOCIATION AREA BASAL GANGLIA b PREFRONTAL CORTEX BRAINSTEM SPINAL CORD VISUAL ASSOCIATION AREA VISUAL CORTEX AUDITORY ASSOCIATION AREA AUDITORY CORTEX CEREBELLUM a Major brain regions involved in motor control, highlighted in yellow. a) shows a lateral view of the left-hemisphere. The basal ganglia are not visible: their position within the brain is depicted in b). DLPFC dorsolateral prefrontal cortex: PMC premotor cortex: SMA supplementary motor area

5. Motor cortex • Premotor motor cortex is primarily concerned with movement in response to external events • Supplementary motor area mainly controls voluntary movement • Both are active during any type of movement • Information from the motor cortex to the spinal cord can be transmitted directly via the pyramidal tract • Brainstem also passes information to the spinal cord via the extrapyramidal tracts • These begin in the association areas which receive input from a variety of motor and sensory sources • The motor cortex also sends information to the basal ganglia and cerebellum • Basal ganglia are important in the initiation of the desired action and the inhibition of unwanted movement • Cerebellumis mainly responsible for the control of movements of greater than one reaction time • Information from the brain is passed down to the muscles by efferent nerves or motoneurons in the spinal cord

6. Feedback • Information from the PNS about the movement is fed back to the brain by afferent or sensoryneurons, situated in the spinal cord • Short loop to the spinal cord • Long loop to the cerebellum • Also all the way back to the somatosensory and motor cortices • To the somatosensory and motor cortices takes about 180 ms before the information can begin to be processed in order to alter an action • It takes about 400-600 ms to alter a movement by a large amount, e.g. a goaltender in ice hockey having to change direction to stop a deflected shot.

7. Long loop feedback • Long loop feedback is to the cerebellum • Takes about 80 ms before information can begin to be processed • Alterations to the movement are limited • It is capable of initiating changes which will result in completion of the originally desired action: based on feedforward it received from the motor cortex • If the situation has changed dramatically, as in the ice hockey goaltender situation, this may not be satisfactory

8. Short loop feedback • Short loop feedback is to the spinal cord • Information can begin to be processed after about 30 ms • Can only make minor alterations to ensure that the original ‘instructions’ from the motor cortex are carried out • Process is called alpha-gamma (-)coactivation • Efferent information from the spinal cord to the muscle is by α-motoneurons, which activate the muscle • Simultaneously, γ-motoneuronsactivate small intrafusal fibres of muscle spindles, which are sensory nerves within the muscle • These sensory nerves ‘tell’ the α-motoneurons if they are over- or under-stretched • The α-motoneuronsin the spinal cord react accordingly and alter the contraction to obtain the originally desired tension

9. Types of feedback • Proprioception • Perception of the body and its position in space • The individual’s ability to know where his/her body is in space and to be aware of the positions of the different limbs • Vestibular feedback • Vestibular apparatus, located in the inner ear, is responsible for balance • Provides information about head position • and the speed and direction in which we are moving • Visual proprioception • Peripheral and ambient vision are more important than foveal • Vestibulo-oculomotor reflex, which is processed by the cerebellum, provides information about head position • Stabilizes the image on the retina during active movement

10. Information processing theory and efferent organization • Open loop control • Motor cortex is responsible for efferent organization • Spinal cord and PNS merely relay information to muscles • No recourse to feedback • Closed loop • As with open loop except that feedback from PNS provides the brain with information to alter ongoing actions • Most movements are under joint open and closed loop control • Initial stages (< 1 RT) open loop but later stages closed loop • Well-learned tasks are controlled by motor programmes

11. A set of muscle commands that allow movement without recourse to peripheral feedback (Keele, 1968) Examples of motor programmes Catching a ball Forehand drive in tennis Handspring Hand writing Motor programmes

12. The individual stores a template or model in LTM They practise: corrections are made until the action matches the template takes place solely in the motor cortex, basal ganglia and cerebellum (Keele, 1968) Then the motor programme is established Motor programmes can be combined to form an executive motor programme e.g. hop, step and jump can be combined to form the triple jump Developing a motor programme

13. The individual stores the sequencing, timing and range of movement Overall timing can change but relative timing of segments can not be altered This has been challenged Bootsma and Van Wieringen (1990) showed that performers were able to alter the timing of different phases of a motor program during execution Feedforward allows for very quick changes (< 1 RT) Classical motor programme theory: storage

14. Motor programmes are specific So how do we store the millions of specific motor programmes that we have? We do not store the whole movement but the location of key points in the movement (MacNeilage, 1970) We do not store specific motor programmes but rather generalized rules or schemas (Schmidt, 1975) We can adapt the schema to any given situation The storage issue

15. Brain sets goal Instructions from the brain are functionally specific run, jump, catch the ball, do a somersault Spinal cord, PNS, joints and muscles take care of the detail of the movement This is known as self-organization Dynamic systems theory and motor control

16. Neurons, muscles and joints form coordinative structures When we move these coordinative structures follow the laws of physics and self-organize to produce the movement In doing this they will take into account the individual’s physical, nervous and perceptual state (his/her organismic constraints) and follow the least effort principle Organismic constraints are known as rate limiters When neurons, muscles and joints self-organize, they form what Bernstein called degrees of freedom According to Bernstein, this control of the degrees of freedom can not be made by the brain. It has to be subconscious and automatic Self-organization

17. Visual guidance of movement • According to Lee et al. (1984), we use  and ̇ to calculate how long it will take us to reach an object • e.g. approaching the take-off board during the run up when doing a long jump • Bootsma and Van Wieringen (1990) showed that, as table tennis players move to hit a ball, they are constantly altering the position of their bat and arm with reference to their position in relation to the ball • Initial stages of the movement are general and become more precise as the bat approaches the point of contact • They used the term funnel shape to explain this • They claimed that this was visually guided

18. Development and motor control: infancy and childhood • Neurological and physiological growth are rapid during infancy and this affects motor control • By 18 months the cell content of cerebellum is at adult level • By 5 years the child’s brain is 90% adult size • During early childhood, physiological growth slows down compared to infancy and the toddler period but is still very noticeable • There are slow increases in muscular strength and endurance, speed, and agility • Flexibility tends to show slight decreases after the age of 10 years • Girls are more flexible than boys • Overall, throughout this period girls tend to be about 1year ahead of boys

19. Development and motor control: adolescence • Girls begin adolescence at about 9 years old and boys about 11 years • Girls continue to increase in height until they are 16 years and boys until 18 years • increase in boys’ weight is due mostly to increased height and muscle mass • Increases in girls’ weight are due to increases in adipose tissue as well as height and muscle mass • Muscle mass in girls increases less than in boys • V̇O2MAXincreases although there is a levelling off for girls at about 12 years • Boys have higher V̇O2MAX values than girls, but this tends to disappear when we measure oxygen uptake against lean muscle mass

20. Ageing • Cardiovascular and muscular fitness peak around the mid-twenties to early thirties • There is then a slow decline up to about 50 years, followed by a fairly rapid decline. This decline accelerates even further at about 70 years • A physically active lifestyle can slow the ageing process greatly • There is considerable shrinkage in areas of the brain which are important for motor control • e.g. the parietal cortex, motor cortex and cerebellum • The older person utilizes more areas of the brain to control movement, especially the prefrontal cortex and basal ganglia

21. Gallahue’s life span model of motor development • A stage theory • In the fundamental movement phase (2-7 years) children learn to perform ‘a variety of stabilizing, locomotor and manipulative movements, first in isolation then in combination with one another’. • Children pick up basic skills quickly but • Skills requiring perception are slow to develop due to poor LTM store • During the specialized movement phase (7-11 years), the individual develops the basic movements into specific actions • Up to the age of about 14 years, the child learns to apply fundamental movements patterns to complex skills • Whether or not this process will continue to be developed in adulthood will depend on the motivation of the person

22. Development and motor performance • By the age of 6 years normal children are capable of carrying out basic motor skills • e.g. walking, running, jumping, catching, skipping, throwing and balancing, at a mature level • Striking and catching are dependent on the development of perceptual skills, particularly dynamic visual acuity • These improve very slowly throughout childhood • During adolescence, improved physiological status aids a rapid improvement in motor skills • Striking and catching develop due to improvements in perceptual abilities • By 12 years perceptual skills are thought to be at the adult level

23. Practical implications of developmental issues • Use of mini-games for children • Smaller size pitches and courts, smaller bats and racquets, smaller balls, lighter equipment • Use of conditioned games • Smaller numbers of players lessens the perceptual and decision-making demands • Games like flag American football and touch rugby lessen the physical issues of tackling