A3.1.7 Motor Control. 10 November 2016 Institute of Psychiatry,Psychology and Neuroscience Marinela Vavla

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1 A3.1.7 Motor Control 10 November 2016 Institute of Psychiatry,Psychology and Neuroscience Marinela Vavla

2 Learning objectives Motor systems: components & organization Spinal cord Descending pathways Areas of motor cortex Basal ganglia Cerebellum Motor system control Optimal feedback control Internal & Inverse models Motor learning

3 The Movement? What is the movement? The starting point of a movement? How is the will related to it? What about self awareness during the execution of the movement?

4 Motor System DEFINITION Produce movements by translating neural signals into contractile force in muscles Plan, coordinate, execute movements Motor behaviour Limb interaction Neural control Scott, Nat 2004

5 Motor system Neural control lspinal level: supports most automatic movements, reflexes, complex multijoint/multi limb sensorimotor responses lcerebral Cortex level: supports voluntary motor tasks, learned associations. Responsible for planning, identification, selection of goals and strategies and mediates the execution of movements Limb mechanics lmotor unit: Motor neuron (MN) + Muscle fibre(s) lmotor unit activity CONVERTS into Muscle Force Motor behaviour lmovement is smooth, lightly adaptable and shows selective patterns of variability reflecting the economy of task relevant features of motor performance

6 Motor System Hierarchical organization: Spinal cord (MN, IN) + Muscle Brainstem Cortex & Basal ganglia Cerebellum

7 Motor System INPUT MOTOR PROGRAM OUTPUT Motor program: is a central pattern generator (CPG) which consists of a group of INs that activate a specific group of MNs in a certain sequence and inhibits other MNs that may counteract the intended movement activated by will and triggered by sensory stimuli Output (different motor patterns): Ramp and Ballistic movements Automatic and Voluntary movements

8 Spinal cord to muscle Blu: Ascending pathways Red: Discending pathways 1.Anterior horn cell in ventral horn of spinal cord 2.Peripheral nerve containing motor and sensory fibres 3.Neuromuscular junction 4.Muscle fibre

Motor System: Sensory component Motor Unit: MN + Muscle Fibre Descending tracts & INs > MN > Supply muscles > Movements Sensory components: can trigger behaviourally meaningful motor acts contribute

9 Motor System: Sensory component Motor Unit: MN + Muscle Fibre Descending tracts & INs > MN > Supply muscles > Movements Sensory components: can trigger behaviourally meaningful motor acts contribute to the control of an ongoing motor pattern and influence the switch from one phase of the movement to another influence the level of activity of one muscle or a group of close synergists help detect and counteract any disturbance of body posture provide information about position of different parts of the body in relation to each other and to external world.

10 Motor System: control Feedback and Feed forward control: Feedback: correction of a perturbation after it has occurred. Feed forward: anticipation of a perturbation before it is initiated & correction before it has occurred.

11 Lateral Pathways Cortico-Spinal Tract (CST) Cortico-Nuclear Tract (CNT) Lateral CST: 70 90% of the motor fibers to the spinal cord. A small uncrossed tract descends in the anterior CST lthe descending motor fibers decussate at the medullary pyramid lspinal cord level: the motor axons descend in the lateral columns making monosynaptic connections with the MNs traveling to distal muscles. & Provide fine control of voluntary movements (e.g. monkeys with CST lesion, can recover the use of all the 4 limbs but unable to make fine finger movement needed).

Ventromedial Pathways Vestibulo-Spinal Tecto-Spinal Pontine-Reticulo-Spinal Medullary-Reticulo-Spinal Substantial input from basal ganglia, cerebellum and brain stem nuclei Located as separated

12 Ventromedial Pathways Vestibulo-Spinal Tecto-Spinal Pontine-Reticulo-Spinal Medullary-Reticulo-Spinal Substantial input from basal ganglia, cerebellum and brain stem nuclei Located as separated tracts in the anterior and lateral white matter within the spinal cord Controlateral and polysinaptic connections to MNs of proximal and axial muscles within the spinal cord. & Involved in the: control of posture locomotion stereotyped movements (e.g. monkeys with lesions in these pathways, fall over when attempt to ambulate/climb).

13 Descending motor pathways Direct neuronal pathway between the motor cortex and the anterior horn cells in the brainstem and spinal cord. Constitutes the Pyramidal tract 85 90% of which which decussates (crosses) at the level of the medullary pyramids. Motor cortex (primarily M1) red nucleus Corticospinal or pyramidal tract reticular nuclei vestibular nuclei In addition to the direct pathway there are several indirect pathways (Extrapyramidal system) which have more input from the basal ganglia, cerebellum and brain stem nuclei than primary motor cortex Fine voluntary movements rubro-spinal tract Lateral pathways (Lateral columns) Spinal cord reticulo-spinal tracts vestibulo-spinal tracts Separate tracts within the spinal cord Locomotion, stereotyped movements, and postural control

Cerebral cortex areas that give rise to the CST: Frontal lobe: M1 (Area 4); PMA and SMA

14 Motor Areas of the Cerebral Cortex (Brodmann areas) PMA/SMA Primary motor cortex lateral view 6 4 Central sulcus Somatosensory cortex Posterior parietal cortex 6 4 medial view Cerebral cortex areas that give rise to the CST: Frontal lobe: M1 (Area 4); PMA and SMA (Area 6) Parietal lobe: Somatosensory (Areas 3, 1 & 2), Posterior Parietal (5, 7, 39 & 40)

according to the level of fine movements required rather than the actual size of the body part

15 M1 and Penfiled s Homunculus (the brains motor map of the body) Electrical stimulation of primary motor cortex during surgery for patients with epilepsy demonstrated a disfigured representation of the body according to the level of fine movements required rather than the actual size of the body part (Penfield) Motor homunculus Stimulation resulted in types of movement rather than movement of individual single muscles

16 Primary Motor Cortex (M1) M1 stimulation: produces muscle movement at a stimulus intensity far lower than in any other part of the cerebral cortex. Cortical neurons activity related to motor acts begins diffusely throughout the cortex and converges in M1. Motor act occurs only after the activity in M1 has reached a peak. M1 neurons encode the force of muscle contraction and the direction of movement. Small groups of motor neurons are controlled by small population of cortical neurons in M1. The control is specific, directed to the most distal part of the limbs, related to the most delicate and precise movements.

17 Premotor Cortex (PMA) (I) Premotor cortex (PMA) Contribution to CST < M1. Electrical stimulation of PMA does not produce muscle movement unless there are higher intensity stimuli when compared to the effective M1 stimuli. PMA prepares M1 for the impending motor act.

18 Premotor Cortex (PMA) (II) Important role in preparing M1 for a specific motor act: PMA activity facilitates multiple motor columns in M1 preparing them for action facilitated M1 neurons are more easily stimulated by stimuli arriving from other areas of the cortex and close to the critical threshold activity required to start a movement. PMA lesions in humans do not cause paralysis but slowing of complex movements. Lack of sufficient facilitation from PMA on M1.

19 Supplementary Motor Cortex (SMA) Cortical electrical stimulations of SMA neurons elicit complex movements involving many muscle groups often entire arm, both hands or postural movements. SMA Ablation of unilateral SMA results in limitation of the ability to perform complex bimanual movements. Functional imaging studies have shown that SMA is not necessary for simple repetitive motor acts that require little thought or preparation. Important for planning complex movements that require conscious effort.

20 Cartoon Anatomy of the Basal Ganglia Basal ganglia: Striatum Caudate Putamen The basal ganglia Globus Pallidus GPi GPe Thalamus (VA/VL) caudate Subthalamic nucleus (STN) STN GPe Substantia Nigra SNr SNc SNc GPi putamen SNr

21 Anatomy of the basal ganglia caudate nucleus thalamus putamen caudate globus pallidus GPe GPi putamen forebrain coronal view subthalamic Nucleus (STN) GPi GPe substantia nigra midbrain

SMA PMC primary motor somatosensory parietal association Putamen projects to i) GPi and SNr (direct pathway) ii) GPe to GPi via STN (indirect

22 Basal Ganglia Circuitry The cerebral cortex (SMA, PMA, M1, somatosensory and parietal cortex) has major projections to the caudate and putamen. SMA PMC primary motor somatosensory parietal association Putamen projects to i) GPi and SNr (direct pathway) ii) GPe to GPi via STN (indirect pathway) Thalamus (VA/VL) caudate STN The GPi and SNr are the only output nuclei of the basal ganglia, which in turn project to the thalamus. GPi GPe putamen SNc And via the thalamus back to the SMA & PMA (movement preparation and planning) SNr NB important Nigro-striatal pathway

23 Basal Ganglia s Functions: Major role in motor control but also other cognitive and behavioural activities. Involvement in action selection. Reinforcement learning (reward). Basal ganglia dysfunction: Parkinson s disease, Huntington s disease, schizophrenia, Tourette syndrome, attentional deficit disorder.

24 Cerebellum The cerebellum contains more than 50% of all neurons in the brain. The cerebellum receives nearly 200 million input fibers.

25 Anatomical and Functional Divisions of the Cerebellum lvestibulocerebellum (Archicerebellum) lspinocerebellum (Paleocerebellum) lcerebrocerebellum (Neocerebellum) Functions: lcontrol equilibrium lregulate postural tone lharmonic/precise coordination of voluntary movements

26 Vestibulocerebellum Vestibulocerebellum: flocculonodular lobe Regulates balance and eye movements. Receives vestibular input from the semicircular canals and sends fibres back to the medial and lateral vestibular nuclei. Receives visual input from the superior colliculi and from the visual cortex. & Lesions may cause disturbances of balance and gait.

27 Spinocerebellum Vermis Spinocerebellum: Vermis Intermediate Regulates body and limb movements. Elaborates proprioceptive input in order to anticipate the future position of a body part during the course of a movement, in a "feed forward" manner. Receives proprioception input from visual and auditory systems, and the dorsal columns of the spinal cord. lsends fibres to deep cerebellar nuclei which in turn project to both the cerebral cortex and the brain stem, thus providing modulation of descending motor systems.

28 Cerebrocerebellum Lateral lobe Cerebrocerebellum: cerebellar hemispheres Involved in planning movement that is about to occur. Receives input exclusively from the cerebral cortex (especially the parietal lobe) via the pontine nuclei (forming cortico pontocerebellar pathways) Sends fibres mainly to the VL thalamus (in turn connected to motor areas of the premotor cortex and M1 of the cerebral cortex) Sends fibres to the red nucleus (in turn connected to the inferior olivary nucleus, which links back to the cerebellar hemispheres).

29 Motor Control (OSTEF) 1 Objectives= Motor task 2 Strategy= define the movement and the strategy to achieve it Cerebral cortex (vision, audition, somatosensory) Basal Ganglia (filter of the different alternatives provided by the cortex until a final decision is made) 3 Tactics= sequence of muscle contraction arranged in space & time in order to achieve a smooth and accurate movement) Motor cortex Cerebellum 4 Execution= activation of MNs and INs generate a goal oriented movement & make the necessary adjustments) Brain stem Spinal cord & 5 Feedback Sensory information as input to cortical areas (somatosensory, visual, auditory, vestibular)

30 Feedback Visual guiding movement and providing critical cognitive information about the location and shape of the objects Vestibular input maintain balance and orientation Somatosensory touch and proprioception (information about joint angle, muscle length, and tension, which is integrated to give information about the position of the limb in space) important for the accuracy of movements and stability of posture

An Example Association cortical areas, cerebellum and other areas Contain multiple brain representations of limb and body position, external objects in space and stored motor memories Prefrontal

31 An Example Association cortical areas, cerebellum and other areas Contain multiple brain representations of limb and body position, external objects in space and stored motor memories Prefrontal cortex Movement strategies need to be devised. Alternative motor sequences filtered through the basal ganglia and back to the cortex to plan and select the best course of action Motor cortical areas and cerebellum Make the tactical decision. Neuronal activation in the brain stem and spinal cord lead to the execution of the movement.

Optimal Feedback Control Scott, 2004 Todorov and Jordan theory Motor commands are corrupted by noise Motor systems can be modelled based on optimal feedback control Optimal feedback control modifies

32 Optimal Feedback Control Scott, 2004 Todorov and Jordan theory Motor commands are corrupted by noise Motor systems can be modelled based on optimal feedback control Optimal feedback control modifies feedback signals to optimize an index of performance, creating a complex link between sensory signals and motor output Feedback control law used to minimise task relevant errors (minimum intervention principle)

Optimal Control Optimal Control Translate from high level tasks into detailed motor programs Execute the task/movement with the lowest cost Example: Arm movement (2 different motor

33 Optimal Control Optimal Control Translate from high level tasks into detailed motor programs Execute the task/movement with the lowest cost Example: Arm movement (2 different motor commands: saccadic eye movement and arm movement) Optimal control strategy (achieve an accurate movement) Cost: movement error specifies the optimal movement. Wolpert and Ghahramani, 2000

34 Estimation and Prediction of State Kalman filter Combination of sensory feedback & forward models to estimate the current state Compensate for sensorimotor delays Reduce uncertainty in the state that arises because of noise in both sensory and motor signals Predicts and Estimates of the state Mental simulation of intended movements & Damage to the parietal cortex leads to inability to maintain such estimates Wolpert and Ghahramani, 2000

35 Internal Model Neural processes that mimic the properties of the limb or the environment Reflect the association between motor commands and limb movements, or vice versa Internal Models: oforward Internal Model Modelling the causal relationship between actions and their consequences oinverse Internal Model Modelling from the desired consequences to the actions

Internal models: Learning Wolpert and Ghahramani, 2000 The difference between the predicted and sensory feedback can be used as an error signal to update a predictive model Internal models

36 Internal models: Learning Wolpert and Ghahramani, 2000 The difference between the predicted and sensory feedback can be used as an error signal to update a predictive model Internal models mustbeadaptable to changes in Short time scale (due to interaction with the environment) Long time scale (due to growth) A feedback controller computes a motor command based on the discrepancy between desired and estimated states. The feedback motor command is added to the feedforward motor command generated by the inverse model. WHY? If the feedback controller command goes to zero, then there would be no error in performance, and subsequently the inverse model would be performing perfectly. NB: Thus the output of the feedback controller can be regarded as the error signal, and used to train the inverse model.

37 Motor learning: components Information extraction Learning features of the task Structural & parametric learning Context & credit assignment Learning via fast and slow processes MOTOR LEARNING Classes of control Stiffness, Reactive & Predictive Optimal feedback control Decisions and strategies Wolpert & Flanagan, 2010

38 Thank you!

Voluntary Movement. Ch. 14: Supplemental Images

Voluntary Movement. Ch. 14: Supplemental Images Voluntary Movement Ch. 14: Supplemental Images Skeletal Motor Unit: The basics Upper motor neuron: Neurons that supply input to lower motor neurons. Lower motor neuron: neuron that innervates muscles,