Motor control? Topics in Motor Function and Dysfunction KAHS Fundamental issues in motor control. Motor control? Motor control? Motor control?

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Topics in Motor Function and Dysfunction Motor control? What is it? KAHS 6150 Why study it?

How different body parts work together to generate movement has been of interest for centuries Motor control? What is it?

Why study it? Who s interested? Who s interested? Rich diversity of interesting problems associated with it Motor control?

1 Topics in Motor Function and Dysfunction Motor control? What is it? KAHS 6150 Why study it? Fundamental issues in motor control Who s interested? Motor control? What is it? How different body parts work together to generate movement has been of interest for centuries Motor control? What is it? While better techniques have been developed to study movement, many fundamental control issues remain unresolved Why study it? Why study it? Who s interested? Who s interested? Rich diversity of interesting problems associated with it Motor control? What is it? Motor control? What is it? Ideal way to study brain function Why study it? Why study it? Broadly ranging practical applications Who s interested? Who s interested? At a more fundamental level... 1

2 neuropsychology Motor control? What is it? : ergonomics PSYCHOLOGY behaviour cognition Motor Control Research ENGINEERING physical systems cells PHYSIOLOGY muscles biomechanics biomedical engineering Why study it? Who s interested? Do-it-yourself Bernstein demo... Degree of freedom problem subcortical structures / cerebellum CORTICAL STRUCTURES target acquisition ( goal ) spinal circuitry MUSCLE ACTIVATION KINETICS joint torques forces force vel. force accel. How do we generate a movement in the face of all this redundancy? CONSTRAINTS! Basic features of reaching Evidence from studies using a psychophysical approach Study motor behaviour to make inferences about underlying control signals 3 characteristics of reaching movements: 1. Straight-line hand paths to target occurs despite more complex joint excursions Minimization principles and invariant characteristics Source: Morasso, EBR,42: ,

Y-axis (mm) Straight hand paths Implies that at some level CNS representing reaching movement in hand-centred, spatial coordinates What if never had vision?

3 Y-axis (mm) Straight hand paths Implies that at some level CNS representing reaching movement in hand-centred, spatial coordinates What if never had vision? Most movements guided by proprioception Hand joint Elbow(deg) Shoulder(deg) 2. Unimodal, smooth, bell-shaped velocity profile of the hand Hand velocity 4 different movements time Source: Morasso, EBR,42: , 1981 X-axis (mm) Source: Sergio&Scott,EBR 122: , Peak velocity and peak acceleration scale with movement amplitude Hand vel. Degree of freedom problem How do we generate a movement in the face of all this redundancy? CONSTRAINTS! Minimization principles Hand acc. Synergies Source: Messier&Kalaska,EBR 125: ,1999. One invariance: equal angles are drawn in equal times Isogony principle each loop drawn in the same time, even though linear distances were different. Suggests: figure is segmented (discontinuity smoothed during execution by viscoelastic properties of the neuromuscular system) timing is a control feature Angle measure Coordination between elevation and medial-lateral rotation ( yaw ) of shoulder and elbow maintained over different wrist trajectories Frontal plane 3-d wrist position elbow shoulder elevation yaw yaw elevation Angle (rad) Time (sec) Sagittal plane Flattened trajectory Joint coupling maintained at expense of path: APPROXIMATE SOLUTION, reduces complexity of non-linear transformation between hand and joint space Source: Lacquaniti et al.acta Psychol ,

Both of these solutions assume the limb position is expressed in Cartesian coordinates(after Descartes: external, spatial, NOT muscle/joint, etc) Still the question of how to produce these drawings

4 Both of these solutions assume the limb position is expressed in Cartesian coordinates(after Descartes: external, spatial, NOT muscle/joint, etc) Still the question of how to produce these drawings since ultimately the positioning of the pen must be coordinated by muscle activity acting about different joints Degree of freedom problem How do we generate a movement in the face of all this redundancy? CONSTRAINTS! Minimization principles Synergies Mechanical properties Evidence that CNS may exploit properties of the musculo-skeletal system to assist in movement control as well property: visco-elasticity of muscles muscles can act as tunable springs First demonstrated in monkey experiment After deafferentation, animal still reaches target even after early initial perturbation attributed to spring-like property of muscle Source, next 2:Polit&Bizzi,J.Neurophys,42: ,1979. Serial order problem: how do we generate a sequence of movements? Spoonerisms Co-articulation patient deficits Serial order problem: where do we generate a sequence of movements? Same sequence, Different effectors 4

5 Serial order problem Perceptual-motor integration problem Degree of freedom problem Serial order problem Perceptual-motor integration problem subcortical structures / cerebellum spinal circuitry CORTICAL STRUCTURES target acquisition ( goal ) MUSCLE ACTIVATION Feedforward - feedback integration KINETICS joint torques forces force vel. force accel. Serial order problem Perceptual-motor integration problem Frame of reference: sensory information integrated into motor plan Degree of freedom problem Serial order problem Perceptual-motor integration problem Frame of reference: sensory information integrated into motor plan Serial order problem Perceptual-motor integration problem These all assume that the movements have been learned! Serial order problem Perceptual-motor integration problem Skill acquisition 5

Skill Acquisition Serial order problem Perceptual-motor integration problem Skill acquisition innate versus learned motor learning and development retention of motor skills innate versus learned

then use fingers to grab Corresponds to rapid increase in the rate of myelination of corticospinal tracts at 12 months responsible for distal musculature Grasp reflex Hang in there, baby!

Skill Acquisition innate versus learned motor learning and development retention of motor skills Fitts 3-stage theory of learning CAN BE THOUGHT OF AS THE DEVELOPMENT OF GENERAL PROGRAMS cognitive

6 Skill Acquisition Serial order problem Perceptual-motor integration problem Skill acquisition innate versus learned motor learning and development retention of motor skills innate versus learned motor learning and development retention of motor skills Grasp development Newborns have grasp reflex (clasp object brought against palm) disappears by 6 months Use palmar grasp until about 12 months then use fingers to grab Corresponds to rapid increase in the rate of myelination of corticospinal tracts at 12 months responsible for distal musculature Grasp reflex Hang in there, baby! Source: Boakes,From Darwin to Behaviorism,Camb.Univ.Press,1994. Skill Acquisition innate versus learned motor learning and development retention of motor skills Fitts 3-stage theory of learning CAN BE THOUGHT OF AS THE DEVELOPMENT OF GENERAL PROGRAMS cognitive stage learn basic procedures to be followed associative stage transition from conscious to automatic control autonomous stage -- this stage involves motor programs i.e., transition from closed loop to open loop control (feedforward) little conscious involvement at this stage Role of feedback in the autonomous stage of learning feedback necessary during learning, but not to the same extent later, skilled performers monitor their performance, and make intermittent corrections as necessary Skill Acquisition innate versus learned motor learning and development retention of motor skills Procedural versus declarative memory 6

Skill acquisition Improvement with practice, motor consolidation Summary Motor control: The study of how the nervous system and the periphery function together to plan and coordinate movement 4 basic

Peripheral issues What do we have that needs controlling?

7 Skill acquisition Improvement with practice, motor consolidation Summary Motor control: The study of how the nervous system and the periphery function together to plan and coordinate movement 4 basic issues: degree of freedom serial order perceptual-motor integration skill acquisition These 4 issues are not independent!! Source: Shadmehr & Holcomb, Science : Peripheral issues What do we have that needs controlling?? Life beyond the central nervous system (I ve heard rumour of such a thing ) Beyond the CNS we have muscles attached to bones, joined at joints Complexity at the skeletal level A few examples relevant to multi-joint limbs: CORIOLIS FORCE - an apparent force that can arise when have more than one segment rotating arises from kinematics of relative rotations, not physical interaction velocity dependent increases with distance Source: Allard et al. Three-dimensional analysis of human movement. Human Kinetics Complexity at the skeletal level Interaction torques Net torque at 1 joint that depends on motion at another joint Example: net torque at the shoulder that depends on motion of the forearm Third: degree of freedom problem already discussed These issues must be accounted (controlled) for in order to choose which muscles to activate, when to activate them, and how much to activate them Source: Gribble & Ostry, J. Neurophys :

Complexity at the muscular level Lots O muscles: degree of freedom problem here, too Complexity at the Muscular level Muscle properties Contraction mechanism: sliding filament theory Muscle:

8 Complexity at the muscular level Lots O muscles: degree of freedom problem here, too Complexity at the Muscular level Muscle properties Contraction mechanism: sliding filament theory Muscle: contraction mechanism Sliding filament theory - physiology myosin filaments move like the oars of a boat on the surface of the thin filaments length of filaments don t change isometric versus isotonic? Muscle: Length-Tension relationship One muscle property that arises from the contraction mechanism Composed of active and passive tension **Functionally this means that the same command from the nervous system can produce varying levels of force** Muscle: force-velocity relationship The rate at which a muscle can shorten depends on the force it is exerting. The smaller the load, the faster the muscle shortens It s a wonder we can move at all so again, **same central command will produce different movement depending on peripheral conditions** 8

Ways to study the neural control of movement 1) Motor psychophysics - behavioural studies Look at patterns of

to gain insight into the underlying central commands Pros & cons: pros: often easy to perform cons: indirect

studies: lesions often wide spread, different between patients, not sure if lesion is the neural substrate

functional imaging fmri and PET (see pages 366-379 in Kandel) measures brain activity by measuring blood

Pros & Cons Pros: non-invasive (fmri), measures realtime behaviour Cons: resolution-temporal and spatial -

neurons under carefully controlled conditions as the animal works Pros & Cons pros: direct way of measuring

isn t The nervous system has to deal with complex issues on a number of levels We ve developed numerous

9 Ways to study the neural control of movement 1) Motor psychophysics - behavioural studies Look at patterns of ERRORS during different behavioural paradigms errors reflect the limitations of the nervous system, can use to gain insight into the underlying central commands Pros & cons: pros: often easy to perform cons: indirect Mean end-point On-axis error Off-axis error Can use subjects and patient groups Problems with patient studies: lesions often wide spread, different between patients, not sure if lesion is the neural substrate itself or part of a circuit Source: Perenin&Vighetto,Brain,111: ,1988 Ways to study motor control Human functional imaging fmri and PET (see pages in Kandel) measures brain activity by measuring blood flow, which presumably is increased in areas that are thinking hard! Pros & Cons Pros: non-invasive (fmri), measures realtime behaviour Cons: resolution-temporal and spatial - still not great Ways to study motor control Neurophysiology can record directly the activity of single neurons under carefully controlled conditions as the animal works Pros & Cons pros: direct way of measuring neural information transmission cons: you have to deal with monkeys. Summary A simple movement.isn t The nervous system has to deal with complex issues on a number of levels We ve developed numerous techniques to study the neural control of movement, all with advantages and disadvantages Topics in motor function and dysfunction Next - What we have upstairs: neuroanatomy Basic neuroanatomy 9

Spinal cord medulla brainstem pons midbrain cerebellum diencephalon telencephalon 7 basic divisions Spinal Cord Contains a lot of intrinsic local circuitry for locomotion ( central pattern generators

some of the spinal cord neural processing properties?

10 Spinal cord medulla brainstem pons midbrain cerebellum diencephalon telencephalon 7 basic divisions Spinal Cord Contains a lot of intrinsic local circuitry for locomotion ( central pattern generators ) majority of motor cortex output to interneurons, so further processing of descending control signals occurring sensory comes into dorsal horns, motor comes out of ventral horns ventral What are some of the spinal cord neural processing properties? TO ADDRESS THIS QUESTION, ELECTRICAL ACTIVITY IN LEG MUSCLES IS ANALYZED WITH THE ELECTROMYOGRAM (EMG) FLEXORS -- RETRACT LEG AND PULL IT FORWARD (SWING PHASE) EXTENSORS -- PUSH LEG DOWN AND PUSH IT FORWARDS (STANCE PHASE) ACTIVITY IN CAT DURING TREADMILL WALKING critical finding was that there are central pattern generators or rhythm generators in the ventral (towards the front) columns of the spinal cord this was discovered in preparations that functioned without feedback or input from the CNS fictive locomotion : still see signals from ventral roots if everything else blocked, even muscle activity Dorsal (sensory) roots cut Sensory feedback important for tuning movements and reflexes Can see reflex reversal depending on the phase of the step cycle that an obstacle is encountered What s the functional relevance of this? Source: Grillner & Wallen, Ann Rev Neurosci, 8:233-61,

swing flexors Role of higher brain structures Subcortical and brain stem areas can affect gait patterns In cats and rats: stance extensors flexors extensors Areas related to speed, direction, posture

nigra STIM HERE affects turning, gait pattern (dopamine cells) CUT HERE, still get locomotion Source: Forssberg J Neurophys 42:936-53, 1979 In cats, can also stimulate circuits directly with

(from cortex to spinal cord), affects locomotion requiring visual guidance Neural circuitry Control system Gait patterns motor-wise, contains early relay nuclei (nucleus: group of cells) for postural

11 swing flexors Role of higher brain structures Subcortical and brain stem areas can affect gait patterns In cats and rats: stance extensors flexors extensors Areas related to speed, direction, posture (dopamine levels) caudate N.accumbens Subs. nigra STIM HERE affects turning, gait pattern (dopamine cells) CUT HERE, still get locomotion Source: Forssberg J Neurophys 42:936-53, 1979 In cats, can also stimulate circuits directly with neurotransmitter to restore locomotion So brain serves more of a supervisory role over central pattern generator (cpg) Sensory feedback acts to tune the cpg Lastly, if lesion corticospinal tract (from cortex to spinal cord), affects locomotion requiring visual guidance Neural circuitry Control system Gait patterns motor-wise, contains early relay nuclei (nucleus: group of cells) for postural control and neck and face muscle control contains part of the reticular formation output from these reticulospinal tracts are inhibitory to extensor and excitatory to flexor muscle groups contains vestibular nucleus (postural control) Brainstem: Medulla Brainstem: Pons Contains pontine nuclei, that relay information about movement and sensation from the cortex to the cerebellum. That s why it s so big in humans. contains part of the reticular formation output from these reticulospinal tracts are excitatory to extensor and inhibitory to flexor muscle groups 11

Brainstem: Midbrain Three midbrain structures motorically important: superior colliculus: involved in controlling involuntary eye movements red nucleus: involved in control of limbs substantia nigra:

Midbrain: Superior Colliculi Two structures on the back (dorsal surface) of the brainstem Right superior colliculus controls eye movements to the left hemifield, and vice-versa Within each structure

receives input from motor cortex and cerebellum. Output is predominantly inhibitory to extensors and excitatory to flexors.

12 Brainstem: Midbrain Three midbrain structures motorically important: superior colliculus: involved in controlling involuntary eye movements red nucleus: involved in control of limbs substantia nigra: works with basal ganglia. Midbrain: Superior Colliculi Two structures on the back (dorsal surface) of the brainstem Right superior colliculus controls eye movements to the left hemifield, and vice-versa Within each structure is an organized map for saccade amplitude rostral caudal left right FIXATION (no movement) ROSTRAL SACCADES (of increasing amplitude) CAUDAL Midbrain: red nucleus & substantia nigra Red nucleus: receives input from motor cortex and cerebellum. Output is predominantly inhibitory to extensors and excitatory to flexors. Mainly concerned with movements of extremities substantia nigra: area with dopaminergic cells that die off in parkinson s disease. Clinically often included with basal ganglia. Ventral Superior colliculus Red nucleus Substantia nigra Cortex Midbrain Pons Medulla Cord Red nucleus Cerebellum Pontine retic. form. medullary retic. form. vestibular nucleus Vestibular apparatus E- F+ E+ F- E- F+ E+ F- Cerebellum Contains more neurons than the rest of the brain! 40:1 input output ratio (a lot of processing going on in there!) midline region = vermis, sides = hemispheres 4 nuclei in humans and apes (3 in others) that functionally may do different things: fastigial = medial nucleus globose & emboliform (interpositus in monkeys on down) = intermediate nucleus dentate = lateral nucleus ventral Diencephalon Two main components: thalamus and hypothalamus all sensory input, except smell, passes through the thalamus. Modulatory role on incoming information. Hypothalamus deals with more maintainence type things 12

Cerebral hemispheres (telencephalon) Cortex (4 lobes) & sub-cortical structures Cerebral hemispheres - organization Localization & lateralization of function Source: Tortora & Anagnostakos Principles

8 46 24 4 6 1,2,3 Cerebral hemispheres - organization somatotopy within an area gradients within an area contralateral representation Source: Penfield & Rasmussen The cerebral cortex of man, 1950,

13 Cerebral hemispheres (telencephalon) Cortex (4 lobes) & sub-cortical structures Cerebral hemispheres - organization Localization & lateralization of function Source: Tortora & Anagnostakos Principles of Anatomy and Physiology, 4th Ed. 1984, Harper & Row. Unfortunately, there are many naming systems! ,2,3 Cerebral hemispheres - organization somatotopy within an area gradients within an area contralateral representation Source: Penfield & Rasmussen The cerebral cortex of man, 1950, Macmillen. Subcortical structures: Basal Ganglia A group of subcortical nuclei. Clinically, the basal ganglia comprise the caudate, putamen, globus pallidus, (subthalamic nucleus*, and substantia nigra*) putamen caudate Cortical layers Histologically distinct layers usually 6, but can vary Globus pallidus *technically, these aren t basal ganglia structures but clinically they re often all tossed together caudal 13

Information transmission in the ol noggin: the systems neuroscience approach convergence, divergence of signals spatial and temporal coding of activity Cortex organized in columns - efficient!

processing can occur in parallel evidence for anatomically distinct streams for processing what an object is versus where it is, and what action to take where yes, in the end, size does matter

14 Information transmission in the ol noggin: the systems neuroscience approach convergence, divergence of signals spatial and temporal coding of activity Cortex organized in columns - efficient! Serial processing within an area, parallel amongst areas More columns = more information processing Separate streams for processing visual information Many transformations / lines of information processing can occur in parallel evidence for anatomically distinct streams for processing what an object is versus where it is, and what action to take where yes, in the end, size does matter Information transmitted via pathways go between hemispheres via corpus callosum what Source: Goodale,Sensory Guidance of Movement,p.25,1998 Frontal and parietal functional pathways Functionally related areas interconnected caudal parietal to rostral frontal areas and vice-versa For the rest of the course... Traditionally considered either / or in terms of processing different types of information (e.g., spatial versus intrinsic) nowadays recognize the basic problem is getting information from the retina to the muscles question becomes WHEN & WHERE many of these transformations occurring in parallel Multiple, parallel processes for transforming sensory signals into identification and action plans Spinal cord injury (SCI) and the search for a paralysis cure Three approaches presently dominating paralysis research Minimization of damage regeneration/reconnection bypassing the damage altogether Source: Jeannerod,Vision&Movement,p.21,

Three problems Death Disruption Demyelination Minimization of damage following SCI Problem 1: Cell death following injury Can

body temperature Moderate inflammation response Source: Miami Project to Cure Paralysis Problem 2: disruption of nerve pathway

graft using peripheral helper cells (schwann) Mary Bunge, Miami Project to Cure Paralysis One problem this research is

Project to Cure Paralysis Instead of patching disruption, a second approach is to REPLACE damaged nerves Use of fetal cells

Remyelination using Schwann cells from the periphery A different approach to curing paralysis: bypass the damage altogether tap

15 Three problems Death Disruption Demyelination Minimization of damage following SCI Problem 1: Cell death following injury Can occur hours/days/weeks post-injury Therapeutic goal: neuroprotection Steroid administration asap Growth factors (proteins) Lower body temperature Moderate inflammation response Source: Miami Project to Cure Paralysis Problem 2: disruption of nerve pathway Unlike peripheral nerves, axons in the brain and spinal cord cannot regenerate Therapeutic goal: regrowth, bridge the gap Prepare graft using peripheral helper cells (schwann) Mary Bunge, Miami Project to Cure Paralysis One problem this research is encountering is getting the graft past the bridge and onto the spinal tissue Source: Miami Project to Cure Paralysis Source: Miami Project to Cure Paralysis Instead of patching disruption, a second approach is to REPLACE damaged nerves Use of fetal cells successful in animal research Problem 3: Demyelination Also get with some spinal cord injuries Again, trying to trigger Remyelination using Schwann cells from the periphery A different approach to curing paralysis: bypass the damage altogether tap into existing circuitry externally In cats, can stimulate circuits directly with neurotransmitter to restore locomotion Source: Barbeau et al. Br Res Rev.30:27-51,

partially paralysed man walking Pen-width electrodes implanted in lower back,

after a lot of training So, a combination of physical and chemical

Third approach: neuroprosthetics Bypass damage.

been shown that even 5 years post-injury, quadraplegics asked to move show

although some evidence that it can be lost if mental imagery not kept up

16 Could you do this in people? In 2002, Nature reported a study using lower back stimulation resulting in a partially paralysed man walking Pen-width electrodes implanted in lower back, gave low level stimulation to spinal cord He can walk up to a kilometer, after a lot of training So, a combination of physical and chemical stimulation might allow access to central pattern generators in spinal cord Third approach: neuroprosthetics Bypass damage.bypass body altogether Use cortical signals to drive robotics Recently it s been shown that even 5 years post-injury, quadraplegics asked to move show cortical activation of appropriate areas So the brain signals are there, although some evidence that it can be lost if mental imagery not kept up Using MI cell signals to communicate in paralysed patients Phillip Kennedy, Emory University Implants electrode into MI cortex Patient learns to think to move cursor on computer screen 16

KINE 4500 Neural Control of Movement. Lecture #1:Introduction to the Neural Control of Movement. Neural control of movement

KINE 4500 Neural Control of Movement Lecture #1:Introduction to the Neural Control of Movement Neural control of movement Kinesiology: study of movement Here we re looking at the control system, and what