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lecture_notes_fall2011 - KIN 3E03/Life Sciences 3K03 Neural...

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Unformatted text preview: KIN 3E03 /Life Sciences 3K03 Neural control of human movement Dr. Ramesh Balasubramaniam Fall 2011 Patient video Why study motor control? Understand the brain and its relationship to behaviour. Integrate physiological and psychological mechanisms of brain function. Learn about motor disorders by studying cases of patients with brain damage. Applications in sport, rehabilitation and robotics. Why do we have a brain? To generate purposeful movements. Movement is the only way Of interacting with the world. Of communicating (speech, writing, gestures) Human motor control Everything we do is by moving our bodies. Perception in the service of action. What is the difference between the human brain and an artificial brain like a robot? Why is the study of movement such a big deal? The problem is not so simple. We still are only scratching the surface. The problem of graceful degradation. Chess playing computers:Yes But can a robot move chess pieces? Psychological Experience 1012 neurons 102 joints 109 receptors 103 muscles Compression from many to few dimensions THE BRAIN's PROBLEM: How to control a large number of degrees of freedom or moving parts? The degrees of freedom problem. Aspects of the DF problem. How to co-ordinate? Coordination: to bring two any two moving parts of the body into a relationship. Specific topics Balance and coordinated reaching Grasping Interceptive actions Timing & social coordination Is there a brain state for every behaviour? Bernstein's problem Most physical tasks can be done in an infinite number of ways. This is possible due to redundant numbers of degrees of freedom. Touch the tip of your nose with your finger How did the inefficient options get eliminated? Problem of selecting the path (or optimal trajectory) is mathematically underdetermined. Understanding how this is done..... This is the crux of the degrees of freedom problem. Patient video One more time... Relate brain structure to brain function How does the brain solve the Degrees of freedom problem? What kind of computations does the brain perform to make successful movements? How does the brain learn these complex movement patterns? Motor equivalence There is more than one proper solution to the degrees of freedom problem Consider the use of multiple effectors The problem of handwriting: Depending on how & with what body part(s) we are writing, (anatomically they can vary greatly) we see common characteristics. This is referred to as motor equivalence Serial order problem The word TULIP Motor planning is in sequences (cannot be explained by a Stimulus-response chaining). This phenomenon is called co-articulation. Important definitions Coordination: The patterning of body & limb motions relative to the patterning of environmental objects & events. Bernstein's DOF problem: Most physical tasks can be done in an infinite number of ways. This is possible due to redundant numbers of degrees of freedom. TOUCH YOUR NOSE Motor equivalence: Use of multiple effector sets (body parts) to achieve the same goal. HANDWRITING EXAMPLE Serial order problem: How does the brain figure out in which order to do things? TULIP Da Brain Brain = 100 billion neurons Synapses = It has been estimated that there are 1 quadrillion synapses in the human brain. That's 1015 or 1,000,000,000,000,000 synapses! Number of connections = 100 billion X 1015. Number of possible behaviours -> Tools: Directions Coronal Horizontal Sagittal I'd rather have a bottle in front of me, than a .... Frontalobotomy What kind of section is this? Coronal (like a crown :3) The evolved brain Neo-Mammalian brain Paleo-mammalian brain Reptilian brain Netherbrain BRAIN + spinal cord = Central Nervous system Hierarchy of CNS organization: the problem for motor control Spinal cord: seat of reflexes. Brain stem: seat of arousal, tuning & basic emotions (Limbic system) Cerebral cortex: the big cheese goes to Subcortical / supraspinal areas Higher level Cortical areas goes to Corticobulbar and lateral corticospinal tracts cross over (contralateral) Ventral corticospinal tracts stay on their side (ipsilateral) CORTEX MIDBRAIN & BRAIN STEM SPINAL CORD Final common pathway Unit of Action: Reflex Reflex arc: Receptor, conductor & effector (Discovered by Sir Charles Sherrington). Stimulus -- Response (knee jerk) Is chaining of reflexes the way movements are organized? NO. for the following reasons. Basic unit of behaviour Cannot be a reflex because of the following: Reflex? No 1. must be activated by an outside agent 2. what happens when there is no stimulus? 3. fast movements where there is no feedback like typing (or piano playing). 4. you can overwrite reflexes depending on context (e.g. walking on hot coals) 5. Production of novel movements. reflexes are not dynamic movements; it is the same movement every single time Spinal cord damage Spinal cord injury (SCI) occurs when a traumatic event results in damage to cells within the spinal cord or severs the nerve tracts that relay signals up and down the spinal cord. Most common are Lacerations (severing or tearing of some nerve fibers, such as damage caused by a gun shot wound /football injury/car accident). Severe SCI often causes paralysis (loss of control over voluntary movement and muscles of the body) and loss of sensation and reflex function below the point of injury, including autonomic activity such as breathing and other activities such as bowel and bladder control. Supermowned. I am a bad person. Deafferentation & Neuropathy Can move limbs, but cannot feel them Only afferent pathways are affected (no feedback going to the brain) Can come from accidents or even diabetes Typically caused by CO poisoning or lacerations, etc. The role of proprioception: case study of Ian Waterman. visual sense required to find his way around, which is extremely taxing http://www.bbc.co.uk/music/dancersbody/body/proprioception.shtml FRONTAL LOBE: contains MOTOR CORTEX Planning, reasoning, movement (map of the body) some aspects of speech (like TULIP) OCCIPITAL LOBE: Seat of the visual cortex Deals with visual information PARIETAL LOBE: Handles skin based proprioceptive information (heat, cold, pressure & pain) Works closely with the motor areas. TEMPORAL LOBE Speech, hearing and Language Great Canadian Discovery Organization of motor cortex reveals a map of the body Wilder Penfield aka Docteur Penfield This is what we would look like if we used the image from the motor cortex Recap Degrees of freedom, motor equivalence, serial order problem Basic neurophysiology: Brain, spinal cord. Role of reflexes, spinal cord damage. Lou Gehrig Stephen Hawking What is common between the two? Amyotrophic Lateral Sclerosis ... and pointy elf ears. Amyotrophic Lateral Sclerosis (ALS) "Lou Gehrig's disease" - motorneurons of the brainstem and spinal cord are destroyed and their target muscles wither away First symptoms are muscle weakness and atrophy Within 3-5 years, the ability to walk, speak, swallow, (and sometimes breathe) is gone Patient retains cognitive function (keenly aware of what is happening) 10 % are hereditary, autosomal dominant; although not all people with defective gene inherit the disorder 20% of familial ALS have a mutation in the gene for the enzyme superoxide dismutase (protects body from free radicals that cause damage to DNA and proteins w/in cells) SUPEROXIDE DISMUTASE SUPEROXIDE DISMUTASE SUPEROXIDE DISMUTASE SUPEROXIDE DISMUTASE SUPEROXIDE DISMUTASE SUPEROXIDE DISMUTASE... Neuromuscular diseases Destruction of motor neurons (from polio virus for e.g) Plegia paralysis Paresis weakness Strategies for recovery. Stem cells Transplantation of glial cells (ensheathing cells) promoting regeneration "regeneration-friendly" peripheral nerves Transplantation of peripheral nerves! THE SIMPLE STRETCH REFLEX. 1. 2. 3. 4. Doctor Taps your knee Quadriceps extend (stretching of the muscle by tapping the tendon) Stretch receptor tells spinal cord (dorsal root) Spinal cord activates alpha motor neuron (ventral root) which results in the contraction of the quadriceps femoris muscle back to its original length Dorsum The back Ventral The front (belly side) SIMPLE VOLUNTARY MOVEMENT 1. Muscles activated by alpha motor neurons Alpha motor neuron activation causes muscle fibers to contract (increase stiffeness by Acetyl-choline production). Thus movement production is done by lengthening and shortening of agonistantagonist pairs. 2. What's going on in this diagram? Motor command Signal sent from motor cortex to the periphery Goes through the spinal cord before it reaches the muscle + motor neurons Can be modified/fine tuned by other parts of the brain. 1. Motor Cortex sends signal to spine 2. Spinal Cord mediates signal 3. Signal reaches muscle + alpha motor neurons The midbrain The MEDIATOR! Controls many sensory and motor functions including eye movement and the coordination of visual and auditory reflexes (vestibuloocular reflex): what is that? Pursuit tracking Automatic processes that are not reflexes (once you've learned to ride a bicycle). Pursuit tracking refers to smooth tracking of fast-moving objects in the horizontal or vertical fields without the requirement of many (or any) catch-up saccades MID BRAIN: 1. Tectum, 2. Tegmentum, 3. Peduncles The Vestibulo-ocular reflex refers to a reflex that serves to stabilize the image on the retina of a stationary object by adjusting the extraocular muscles to allow for the compensatory rotation of the eye Cerebellum Between the cortex and brainstem sits the most important organ of movement. Locus of time, motor learning, posture. While voluntary movement is largely cortical, most learned physical activity is cerebellar. e.g. Riding a bike, lifting weights Builds models of the world (Dyslexia & Autism). Plays a large role in prediction (remember the Calvin & Hobbes example from lecture 1). He will talk more about this later CEREBELLUM (cerebellar cortex) Similar circuits in fish, mice & humans The cerebellum 1) The cerebellum handles a lot of information. It gets 200 million inputs all the time. In comparison the optic nerve has around 1 million fibres (when the eyes are open) 2) Purkinje cells: input-output operators of the cerebellum. 3) Talks to both sensory and motor cortical areas. Coordinates with the parietal and frontal lobes 4) Hemispheres project ipsilaterally. < This is a big one, the cerebellum projects IPSILATERALLY (the side the nerves originate from is the side that they innervate on the efferent end and vice versa) Cerebellum ANTERIOR Receives proprioceptive input from spine and trigeminal nerve (lateral zone) (medial zone) POSTERIOR Vestibulocerebellum: Equilibrium & stability Vestibular system Receives sensory information about balance and equilibrium from the ears, NOT the spine 'Vestibulo' always refers to stability (balance) and equilibrium: damage to the vestibulocerebellum results in a modified sense of balance and/or gait Spinocerebellum: Receives sensory information from the spinal cord (proprioception) Important for smooth control of movement. Especially of trunk coordination. Chronic alcohol abuse destroys this area. Have you ever been pulled over for drunk driving? Speaks about the coordination tests done for drunk drivers (walking in a straight line, etc.) Neocerebellum Interfaces with the pre-motor cortex (Area 6) Does not receive input from spinal cord But gets heavy projections from cortex Efference copies get sent here Internal models of the world Lesions cause ataxia (clumsiness) Video of cerebellar patient What happens when there is damage to the cerebellum? Issues with posture, messy gait, tremors, etc. Prediction, timing, sensorimotor skill all deteriorate More about this when we go into details about motor disorders. Cerebellar ataxia (left-unilateral) Ataxia: lack of muscle coordination Cerebellar atrophy (degeneration) One more time ... Movement fundamentals Hierarchy in the CNS Spinal cord damage, Deafferentation, ALS Midbrain Cerebellum Recap Role of reflexes, spinal cord damage Deafferentation Basic neurophysiology: Brain, spinal cord. Cortex, descending motor systems, cerebellum Motor homonculus somatotopic map Cerebellar disorders Motor cortex afferent nerve fibers going back to the brain from the periphery do not work due to damage, making it difficult for the brain to properly coordinate movement and sense the world around it (e.g. Ian Waterman) Motor cortex Somatotopic map (also called homunculus) Each part of the cortex uniquely corresponds to a part of the body Neurons in the motor cortex have a tuning curve Adapted from Georgopoulos, A.P., Neurophysiology of Reaching, in Jeannerod, M. (Ed.), Attention and Performance XIII: Motor Representation and Control. Hillsdale, NJ: Lawrence Erlbaum Associates, 1990, pp. 227263 Cortical Motor System Primary motor cortex Execution of movement [area 4 - M1] Somatopically organized Massive descending projections to spinal cord (PARESIS) Damage => pronounced weakness in affected body parts Stimulation => simple mov't in small muscle groups Cortical Motor System [area 6 - SMA/PMC] Pre-motor cortex Movement planning/sequencing Many projections to M1 But also many projections directly into pyramidal tract Damage => more complex motor coordination deficits Stimulation => more complex mov't Two distinct somatotopically organized subregions (Supplementary Motor Area) SMA May be more involved in internally generated movement (e.g. movements from MEMORY) Pre-motor areas May be more involved in externally guided movement (e.g. movements GUIDED visually) Cortical Motor System Posterior parietal cortex (PPC) Sensory guidance of movement [areas 5 & 7] both pre-motor cortex and posterior parietal cortex project into pyramids Many projections to pre-motor cortex But also many projections directly into pyramidal tract Damage can cause deficits in visually guided reaching (Balint's syndrom) and/ or apraxia Likely part of the dorsal visual stream ('where' - guidance and 'how' - action) (Apraxia: cannot execute motor commands despite knowing how and desiring to) One more time... Cortex, descending motor systems, cerebellum Motor homonculus somatotopic map Cerebellar disorders Motor cortex: population codes sensitive to direction Next lecture: other motor areas of the brain. Recap Cortex, descending motor systems, cerebellum Motor Command: Population codes sensitive to direction Cortical motor systems: M1, SMA/PMC, Posterior Parietal cortex Different movements have different cortical activations Externally guided movements Novel movements that are visually guided Internally guided movements Well-learned self guided movements Detection of self movement Cerebrospinal tracts send message via inferior olive to the neocerebellum to correct errors (EFFERENCE COPY) It is early in the morning. Do you know where your limbs are? How do you know that your arm moved? EFFERENCE COPY or COROLLARY DISCHARGE Why you cannot tickle yourself? SMA (internally guided) is active even when imagining movements 1.Cerebral cortex 2.Basal ganglia 3.Brain stem 4.Cerebellum REVIEW OF KEY BRAIN AREAS Basal ganglia Controls force production Fine tunes movements like cerebellum Produces a neurotransmitter that inhibits acetylcholine (called dopamine) Also involved in making movements smooth Damage to BG causes Parkinson's disease. What is common between these people? Parkinson's disease, and low nose bridges. Video of Parkinson's patient Smoothness of movement is compromised Rigidity, tremor and slowness Shuffling gait and bradykinesia can be alleviated by lines on the floor or L-dopa injections (temporary) Rigidity & Tremor at rest Shuffling gait, Bradykinesia (slowness) when moving Basal ganglia disorders Parkinson's disease (PD) "shaking palsy" 1817, James Parkinson ~ 1/4 million people nationwide suffer from PD Strikes men slightly more than women and Found most often in patients over 50 with ~10% of patients <10% of cases are afflicted with "young-onset" PD under 40 (only those younger than 40) from Dopamine and acetylcholine balance is lost (Not enough dopamine) PD symptoms Tremor at rest Slow movements Shuffling rather than walking Impaired implicit motor/cognitive memories (postural corrections, non-verbal communication) Dementia 20-60% of individuals - Cognitive and motoric slowing - Executive dysfunction and poor memory retrieval not sure why it causes dementia Trajectory formation in a Parkinson's patient Note the pattern of EMG activity Note the shakiness/ tremor envelope What causes this? Not enough dopamine So, acetylcholine builds up Muscles become stiff and contract too much. Creates rigidity, tremor and slowness. Imbalance primarily between the excitatory neurotransmitter Acetylcholine and inhibitory neurotransmitter Dopamine in the Basal Ganglia DA Not enough Dopamine~ ACh L-Dopa: delays the breakdown of naturally occurring dopamine, allowing accumulation in surviving nerve cells. Side-effect: dyskinesia (wobbling, involuntary limb movements) One more time...... Force and action switching mediator SMA is internal goal response mediator PMC is external stimulus response mediator Sensory input helps correct movement or initiate countermovements One more time... Motor command Cerebellar function & efference copies Basal Ganglia Parkinson's disease. Dopamine Ach balance L-dopa therapies Adapted from Wichmann, T., and DeLong, M.R., Functional and pathophysiological models of the basal ganglia, Current Opinion in Neurobiology 6 (1996): 751758 Normally, the thalamus actively excites the cortex based on the degree of thalamic inhibition by the globus pallidus and substantia nigra of the basal ganglia. Notice overly stimulated thalamus (lack of thalamic inhibition from SNr/GPi) results in ticks and jerks due to overstimulation Notice inhibited thalamic signal: less stimulation of the cortex and thus less movement/ spinal cord activity GPe is also inhibited too much Adapted from Wichmann, T., and DeLong, M.R., Functional and pathophysiological models of the basal ganglia, Current Opinion in Neurobiology 6 (1996): 751758 Video of Huntington's patient Notice the involuntary tics. AUTOSOMAL DOMINANT Men tend to express the gene Females tend to be carriers 50/50 incidence (AD) trouble sleeping due to tics/jerks Parietal Cortex: Discovery of Mirror Neurons Mirror neurons: The cells that selectively discharge when a person executes particular actions as well as when the person observes an other individual executing the same action (discovered by Rizzolatti in Italy). USEFUL FOR Action recognition Understanding (assigning meaning to other's actions) Associative memory for actions Areas with mirror neurons: - Ventral premotor cortex (near Broca's) Imitation based learning. - Superior temporal sulcus - Inferior parietal area (near Wernicke's) Human See, Human Do Evidence of mirror neurons in humans from fMRI studies Mouth Hand Foot Viewed non-object-related actions - chewing, reaching, kicking Motor areas Parietal areas Viewed object-related actions -biting an apple, grabbing a cup, kicking a ball Found in both frontal (motor) and parietal cortical areas. Mechanisms of action Observation & Imitation (mirror neurons) Role of transformation of object dimensions in visual space into motor specific signals. NOW................. How is sensory information used in action? How is the parietal lobe involved in actions? Vision and Action How does visual information reach the motor cortex? What are the basic functions of vision with respect to movement control? PARIETAL CORTEX FUNCTION Egocentric frames of reference: representations of movements in posterior parietal cortex T wo independent pathways for visual information (Milner & Goodale). DORSAL STREAM DORSAL: To parietal lobe from occipital lobe (where) VENTRAL: To temporal lobe from occipital lobe (what) VENTRAL STREAM DORSAL STREAM DORSAL STREAM: Dorsal stream from visual cortex toward parietal lobe (roughly toward the top of the brain). Sometimes called the "where" pathway (as in location and/or motion) or the "how" pathway (as in how do I take action about the stimulus). VENTRAL STREAM Ventral stream from visual cortex toward temporal lobe (roughly toward the bottom of the brain). Lesions disrupt object discrimination but vision for action is ok. Sometimes called the "what" pathway implying its role in conscious recognition. Form agnosia: Milner & Goodale's patient DF DF could not recognize or draw an apple or a book by looking at them, but could draw them from memory or recognize the held objects. Visual pathways in action: HOW ? WHERE? DORSAL WHAT? VENTRAL Right Parietal lobe lesions Problems with personal space (left and right) and neglect (ATTENTION DEFICITS) Distorted "personal space" in patients with right parietal lobe lesions ("hemi-neglect") Profound indifference to objects and events in the left side of the world, sometimes including the left side of their own body, but not blindness per se (forced attention leads to perception) Neglect within and between objects Ellen, a stroke patient, before the mishap, was described as "Martha Stewart perfect". (her clothes and makeup ) Afterward, still true for right half of face (lipstick, mascara, rouge, etc) and hair (styled), but hair not combed on left and "it was almost as though someone had used a wet towel to erase all of the makeup on the left side". While eating she ignores food on the left side of the plate. When looking in a mirror at an object placed near the left of her face (which seems on the right in the mirror), when asked to reach for it with her right hand tries to reach through the mirror. By changing the mirror's orientation, an object seen to the right behind her head she successfully reaches on the first try. What is going on with left parietal lesions? Right hemisphere has a particular role in spatial representations (but this is not mirrored in the left side) Left parietal lobe is involved in attention but not in the same way. IDEOMOTOR APRAXIA Show me how you would slice bread. Patient makes a fist and pounds table When bread and knife are present then the patient improves but is not very good with the task (2) IDEATIONAL APRAXIA Impairment in carrying out sequence of movements that are components of a behavioural script, while being able to carry out each one alone (e.g., use of a tool appropriately) SERIAL ORDER PROBLEM. Problems with attention demanding tasks Can also be caused by frontal lobe damage especially in the pre-motor areas. Premotor cortical (PMC) areas of the contralateral hemisphere are essential for skilled movements PMC receives input from the parietal cortex where action representions are stored. Parietal lesions can thus cause ideational apraxia in both contralesional and ipsilesional limbs. Overview of concepts Movement Neurophysiology Perceptually guided action Dorsal & Ventral streams Vision for recognition; Vision for action Parietal Lobe Pathologies: right: Neglect Left: Apraxia Movement planning Supplementary motor area Frontal lobe Fine tuning movements Cerebellum Basal Ganglia (dopamine regulation) Projection to ? Motor programs & schemas (part three) One more time... Vision and action Mirror neurons and action Two visual pathways: dorsal and ventral Right parietal damage: hemi-neglect Left parietal damage: apraxia ...
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