Chapter 8 part1 - Lecture notes Sensorimotor System PDF

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Claire Scavuzzo...

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Chapter 8: sensorimotor system SENSORIMOTOR SYSTEM • Sensory input guides motor output • Complexity of simple movements – Control of voluntary behaviour – Example: grocery store cashier • Movements appear effortless • Require combination of sensory changes • Well trained automatic movements – Experience integrates movements into smooth sequence • Compared to sensory systems – Information flowing top down rather than bottom up – Higher level decide what moves to do next then make then happen, top down hierarchy HIERARCHICAL ORGANIZATION • Directed by commands from highest levels à lower levels – Association cortexàmuscles • Higher level goals, will recruit the appropriate muscels to carry out goal • Association cortex specifies general goals; not specific details • Association cortex: higher level goals then recruit the muscles, then those neurons modulated • Muscles are the lowest level – Higher levels free to perform more complex functions – Neurons then get modulated by other areas of sensorimotor system – Muscles: lowest level. Association cortex: highest • Parallel structure – Feedback bidirectional: sensory systems feedback to motor system : where is your arm right now so you can interact • And between functionally segregated levels: those at lower level hierarchy carrying out really specific motor outputs – Signals flow between hierarchical levels via multiple paths • Association cortex can exert control in more than one way – Association cortex directly inhibit eye blink reflex to put in contacts • Functional segregation – Each level composed of different neural structures • Each structure performs different function MOTOR OUTPUT GUIDED BY SENSORY INPUT • Allow for Flexiblilty in changing environment: if we walk in terrain that turns into gravel then ice we know we need to slightly adapt so we don’t fall • Monitor effects of own activities – Fine tune activities

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Motor and sensory are next to each other although in different lobes, they are sharing information – Parietal: somatosensory, frontal: motor – Motor cortex: frontal, central sulcus in the middle Sensory feedback – Sensory organs monitor body’s responses • Feed information into sensorimotor circuits – Direct the continuation of responses – Many responses are controlled unconsciously by lower levels • Efficiency • Leave out higher levels • Carried mainly in the spinal cord: allows us to carry out ongoing motor processes and free up higher levels of our brain Some movements require no sensory feedback: like swatting at a fly, one root motor output not something that needs to be corrected, once you start it can’t be modified – Ballistic movements • All-or-none; high speed; ex:swatting a fly • Once initiated cant be modified • Not influenced by sensory feedback during the motor output • Eg. Hammer could miss and hit your finger GO: man with too little feedback – Destroyed somatosensory nerves of arms, but still had the motor nerves – Will drop something and wouldn’t realize: looked or heard but would not know the object was slipping from his grasp: – No indication of how much pressure exerted • Had to keep visual check on progress (ex: carrying suitcase) • Visual feedback unable to help in writing or holding cup of coffee • Things slipped from grasp

LEARNING CHANGES LOCUS OF SENSORIMOTOR CONTROL • When first learning higher levels involved, we get better and better but we also change where in the brain is involved in doing it • As we get better and better we use less of our higher level brain • First, recruits higher levels but then as you practice task gets carried out by lower levels • Well learned Actions coordinated into sequences of prescribed procedures carried out by lower levels • Initial stages of learning under conscious control – After practice: responses organized into continuous integrated sequences of action without conscious regulation • Typing, swimming, basketball, knitting, playing piano GENERAL MODEL OF SENSORIMOTOR SYSTEM FUNCTION • Reverse to the sensory system • Association cortexàmotor pathwaysà skeletal muscle

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3 principles of sensorimotor function: 1. Hierarchically organized 2. Motor output guided by sensory input: to have the most efficient we don’t need appropriate sensing 3. Learning can change the nature and locus of sensorimotor control: need to recruit less and less higher level 4. Same principles govern large efficient company, free up to make more complex tasks • Evolving in competitive environments

SENSORIMOTOR ASSOCIATION CORTEX • Top of hierarchy • Association cortex to levels of muscles • 2 major areas necessary to initiate movement – Posterior parietal cortex – Dorsolateral prefrontal cortex: receiving information from posterior parietal cortex but also has access to high level goals, Guided by the sensory information in the environment but also high-level goals POSTERIOR PAREITAL ASSOCIATION CORTEX • Important for directing attention towards objects we need to have motor interaction • Neurons responding to the intention to move • Objects in this area responding to intention • Integrates information on body position and objects in space – Directing attention – Intention to perform an action or knowledge of having performed an action • More conscious control of movement

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Receives input from visual, auditory, and somato sensory systems Output goes to: – Motor cortex: aware of overall goals – Dorsolateral prefrontal cortex – Secondary motor cortex – Frontal eye field: I know my keys are over there so I have to go look • Conscious controls eye movement

PPC mosaic of small areas • Patches of cells responding to different parts of the body • Specialized for guiding movements of: eyes, head, arms, hands • Encoding intent to move of idea of it • Stimulate in patients undergoing surgery (Desmurget) – Low: intention to perform action, I feel like wanna do this, can record and know exactly what parts of the body the person wants to move – High: thought they carried out the intended action but did not do the intended action • No action performed in either case • Record from tetrapalegic – Activate cells by imagining actions • Trained computer on cell activity and corresponding imagined actions: “motor imagery” – Imagined goals, imagined trajectories of limbs, different types of movement DAMAGE TO POSTERIOR PARIETAL ASSOCIATION CORTEX • Sensorimotor deficits that are more of an issue with knowing where objects are in space relative to anything else – Perception and memory of spatial relationships – Reaching and grasping accuracy – Issues with control of eye movement, can’t just move the eyes where you tell them – Attention: will stop attending to like one half of space APRAXIA • Disorder of voluntary movement, can’t have appropriate

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– Like if you ask them pass me the pencil, can’t. but if you tell them to write something the will grab pencil and do it – Not due to motor deficit (paralysis/weakness) – Not that they don’t understand but they can’t do what you ask them to do – Not due to deficit in motivation/comprehension Cant make specific movements when requested to do so – Especially if movements out of context • Ex: imagine hammering a nail (but no hammer available) – Can make same movements when not thinking about it Bilateral symptoms; unilateral damage – Left posterior parietal cortex, not many other obvious deficits in left posterior parietal damage – In right, there is more obvious

CONTRALATERAL NEGLECT • Stop attending to half the space • Inability to respond to stimuli on opposite side of damage – Often right posterior lobe – No other sensorimotor deficits – Stop attending to half space, ignores half of space • Right posterior parietal lobe: directing attention towards one side or another • Not conscious perception, but some unconscious level knows there’s something going on • Left side of world doesn’t exist – Motor and sensory fully intact – Left of their bodies (egocentric left) – Tend to not respond to left sides of objects; regardless of location in visual field • Neurons have egocentric and object based receptive fields – Items not conciously perceived but unconciously processed • Objects presented to same spot are not noticed, but subjects tend to look in that same spot in subsequent trials • Can identify incomplete drawings if complete images shown to neglected side previously DORSOLATERAL PREFRONTAL ASSOCIATION CORTEX • Receives input from PPC: knows the intentions to move and where objects are in space • What objects do we want to interact with • Projects to – Secondary motor cortex – Primary motor cortex – Frontal eye field – Posterior parietal cortex • Evaluate external stimuli • Initiate reactions to external stimuli • Neuronal activity depends on

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Object characteristics Location of objects Combo of both Motor responses to objects • Fire before the response • Continue to fire until response complete, stop once the motor output is complete • Dlpfc neurons first to fire in anticipation of motor responses – Decisions to initiate movements may occur here » Decisions depend on pp interactions

SECONDARY MOTOR CORTEX • Receive input from association cortices • Output to primary motor cortex • 2 major areas – Supplementary motor area • Extends into longitudinal fissure, rests on top of cingulate body – Premotor cortex • Lateral surface of frontal lobe • Anterior to primary motor • Right in front of primary motor cortex • What the flow of information is: don’t know what each does in terms of processing • 7 areas in each hemisphere – Evidence from neuroanatomy and neurophysiology of monkeys • Similar to humans • Still actively researched – 2 sma • Sma and pre sma – 2 premotor • Dorsal and ventral – 3 small areas • Cingular motor areas • In cingulate cortex • There are many sub areas but what they all do in terms of processing we don’t know • Electrical stimulation of an area of m2 leads to complex movements – On both sides of the body – Neurons become more active prior to movement and continue activity until movement finished • Involved in programming specific movement patterns – After dlpfc input on general instructions • Imagining picking up object activates: – Sma, premotor and cingulate motor

MIRROR NEURONS • Premotor cortex • Fire when performing a goal directed hand movement – When observing another individual perform same goal directed hand movement • Rizzolati lab (1990s): recording monkey as they pick and sort objects, depending on the task the animals were given, what different neurons in premotor cortex were encoding for this – Same neurons that were active were firing when she was picking up peanuts and putting them in the bowl as when the monkey picke dup and put in the bowl – Neurons encoding what the action is not the action itself – When we are engaged in the task and when we are observing the task, but specific to what the goal of the action is Mirror neurons encoding goals and understanding of actions • Fire when reach for goal object (ie toy) but not another object (ie hammer) – Some neurons fire equally as robustly when watching experimenter pick up toy but not hammer • Testing what the neurons understand – Identify neurons that fire when experimenter grasp an object – Then a screen was placed in front of the object – Half neurons fired as robustly • Monkeys only could imagine the object was grasped; not perceived it...