Motor Learning (PHYL 4518) Fall 2024 - Week 6 PDF

PHYL 4518 Motor Learning F2024 – Wk 6 Zoe Chan, PhD [email protected]  Stretch-shortening cycle Plyometric training More stiff Can store and High-effort power training with release more...

PHYL 4518 Motor Learning F2024 – Wk 6 Zoe Chan, PhD [email protected]  Stretch-shortening cycle Plyometric training More stiff Can store and High-effort power training with release more energy forceful eccentric phase followed by an explosive rapid reversal of the concentric phase ↑ tissue stiffness > ability to More compliant store more elastic energy Can store and Static stretching release less energy ↓ stiffness of muscle-tendon complex Absorb and dissipate force Controlling force output Rate coding Increase firing rate Summation of force Motor unit recruitment Type I > Type IIa > Type IIx Simultaneous contraction of multiple MUs 10 0 85 Smaller Unit Recruitment Voluntary Motor muscles Larger muscles Mix and match of the 2 % Maximal High force (e.g., 100% force production), predominant strategy: 30 50 10 0 rate coding % Maximal Voluntary Force Production  Understand how the CNS creates a plan and initiates a motor action, and how it responds to feedback Compare open-loop and closed-loop control Identify evidence for existence of motor programs Today’s learning objectives  Before the motor command… Planning Movement begins with the will to move Intention to move Two main systems that contribute to the initial intention and planning: The reacting brain The thinking brain  The Reacting Brain Limbic system (multiple regions of brain) Memory Emotional control Limbic Motivation system Hormonal regulation Instinctual processes (sexual drive and feeding)  The Reacting Brain Emotional motor responses can initiate Cerebra l Cortex from sensations, or from own mind Limbic Emotional motor system Basal ganglia responses (e.g. fight or flight) have two potential paths: Directly to brainstem Basal ganglia  cortical Brain stem areas (further modification) Actions  The Thinking Brain Motor plans are planned and initiated from a cognitive frame of Cerebral Cortex reference Association cortex Direct cognitive control and executive decision making Movement planned Basal ganglia from Association cortex Cerebellum (parts of cerebral cortex) Basal ganglia Cerebellum The Thinking Brain Take into account Movement goal Cerebral Cortex Memory Motor Association Emotional state cortex cortex Sensory info from Thalamu s recent and long ago movements Basal ganglia Predicts outcome and Cerebellum takes variability into account Relayed to motor cortex via thalamus  The Thinking Brain Senses Motor cortex refines movement, initiates Sensory motor plan Cerebral Cortex cortices Sends down pyramidal Motor Association cortex cortex and extrapyramidal tracts Thalamu Idea for movement can s be initiated by sensory Basal ganglia input or arise from brain Cerebellum Can be done rapidly, without paying Brain stem/ attention Spinal cord Motor Program Unit 5 Motor Programs PHYL 4518 Motor learning F2024 – Wk 6  Modeling CNS functioning What happens in the brain to determine our actions? Motor Program: Pre-structured set of movement commands that defines and shapes movements Created and stored within CNS Responsible for the grading, timing and coordination of muscular activities necessary for a specific movement  Control of Movement: Open-loop vs. closed loop Two ways in which movements could be controlled Open-Loop Closed loop Open-loop control: General Concept Actions that are initiated but do not change in response to whether they are successful i.e. Do not use feedback Example: Traffic light has pre-set cycle If accident occurs, light will still cycle even though no longer effective Most effective in stable The light is green, but you should not g environments  Open Loop Control in Motor Control e.g. see puck 1. Instructions are coming towards compiled by our central you and decide to take a shot nervous system in Input Motor Program advance of a rapid Stimulus movement Occurs in brain Identification These instructions Spinal Cord called a Motor Response Selection Program Muscles 2. Sent to our muscles Movement Programmin so that they execute g Movement the movement without the In an need entirely for feedback open-loop system, each new movement or change in movement requires the generation of a new motor program  Motor Programs as Open-Loop Systems Many movements, especially rapid/discrete, seem to be controlled this way No time to process info about movement errors Must plan movement in entirety Example of Baseball swing: 1. Evaluate and process speed and direction of ball 2. Make decision on whether to swing 3. Swing is programmed as to speed, trajectory, and timing 4. Control passes to effectors (muscles) for movement execution Evidence for Motor Programs How do we know that movements can be planned and created ahead of time, in their entirety, without the use of feedback? 1. Reaction time Response complexity effects Startled reactions 2. Deafferentation 3. Central pattern generator 4. Inhibiting actions 5. Muscle activity in blocked movements  1. Reaction-time: complex responses Simple reaction time (RT): measures information processing More complex responses have slower RT i.e. It takes longer to plan a complex movement 208 ms E.g. Henry and Rogers experiment Reaction Time 195 ms Simple RT with 3 different conditions 1. Lift finger 150 ms 3 2. Lift finger and slap ball 2 3. Lift finger, slap ball, push 1 button, grasp near ball Low mediu High Movement m complexity  1. Reaction-time: startled reactions Reaction time tested When you hear the beep, hit target the with hand 2 conditions “Beep” target 1. Regular beep 2. Loud horn that startles participant (unexpected) In both conditions, the correct movement is performed Same motor program Horn to startle participant But startled reactions are upet al.toExp100 Ossanna Brain Resms faster! 237, 71–80 (2019). Learn more about the study here.  2. Deafferentation Experiments Deafferentation – severing afferent nerve bundles Does not affect motor pathways monkeys can: Deafferented Climb Play Groom Feed Balance Some difficulty with fine finger control Therefore, theories of movement control would be generally incorrect if they REQUIRED sensory information  3. Central Pattern Generator Central Pattern Generators Areas of the brainstem or spinal cord that control a genetically defined movement pattern E.g. Swimming in fish, Chewing in hamsters, slithering in snakes, walking in humans? Initiated by brief triggering stimulus, occurs even with deafferentation Very similar to motor program  4. Inhibiting Actions Experiments where participants must stop movements after they have initiated Point of no return 150 to 170 ms before the movement initiated Finger lifting experiment Lift finger at “800” 800  4. Inhibiting Actions Example: a baseball check swing Longer movement time Motor program released for carrying out entire swing unless another motor program is initiated telling it to stop There is a point of no return. You cannot stop a movement once it’s initiated and the motor program is released.  5. Muscle activity in blocked movements Participants told to extend elbow Agonist (triceps) and antagonist(biceps) EMG measured 2 conditions Normal extension Extension blocked Results Both conditions had the same pattern of muscle activation, despite blocked movement (and therefore feedback) in one condition  Major Roles of Open-Loop Organizations Determine which muscles contract when, how forcefully, and for how long To organize the many degrees of freedom of the muscles and joints into a single unit To determine postural adjustments necessary to support the upcoming action E.g. bicep pull experiment To modulate the many reflex pathways to ensure that the movement goal is achieved  Control of Movement: Open-loop vs. closed loop Two ways in which movements could be controlled Open-Loop Control: A type of system control in which instructions for the effector system are determined in advance and run off without feedback Closed loop Control: A type of system control involving feedback, error detection, and error correction that is applicable to maintaining a system goal.  Closed-Loop Control Systems: General Concept Example Desired state is set (20oC) Sensory information measured and compared Error to expected temperature Executive Any difference detected as error (e.g. too System cold) Error transmitted to executive to decide what to do to eliminate error (e.g. decide to turn on furnace) Comparato Command sent to effector (furnace turns on) r The action returns the system to the desired state (20oC) This information is sent to the executive, and Effector the cycle continues (e.g. furnace turns on and off all day to maintain house temperature) System Sensory info Desired state: Actual state 20oC Negative feedback loop!  Closed-Loop Control in Human Performance Reaching to pick up cup Visual info about hand’s position relative to cup represents feedback (i.e. information about the movement outcome) Difference in hand location and desired location represent errors Executive determines correction and modifies an effector Most movements have several feedback sources  Closed-Loop Control in Human Performance Input Stimulus Error Identification Response Selection Comparator Motor Movement Program Programmin g Spinal Cord Proprioceptive feedback Muscles Exteroceptive feedback Movement Closed-Loop Control: Feedforward Input Stimulus Error Identification Response Selection Comparator Motor Movement Program Programmin g Spinal Cord Anticipated feedback Proprioceptive feedback Muscles Exteroceptive feedback Movement  Closed-Loop Control: Feedforward Anticipated feedback (also called feedforward info) Sensory consequences that are expected to arise Why can’t you tickle yourself? If anticipated feedback matches actual feedback, then there is diminished perception of sensation Example 2: Force escalation between siblings Shergill et al., 2003 38% increase in force between each turn  Limitations of Closed-Loop Control Models 1. Very Slow Feedback must be sent to executive, and information must be processed (seen as reaction time) Example: Tracking tasks (follow a moving target) Only about 3 corrections per second are possible E.g. bouncing football is hard to grab  Limitations of Closed-Loop Control Models 2. Rapid, discrete tasks would be impossible under this model E.g. texting, playing guitar These movements occur too quickly to process info before the movement is complete Therefore, these movements must be programed in advance Motor Program Theory: Closed-Loop and Open Loop Control Closed loop = Open loop with feedback In most tasks, motor behavior is neither open- nor closed-loop alone but a complex blend of the two Slow movements  Control dominated by feedback Fast/brief movements  Open-loop dominates