Motor Learning

Intro to Motor Learning
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• Motor learning has been described as a set of processes associated with practice or experience leading to relatively permanent changes in the capability for producing skilled action
- A process of acquiring the capability for skilled action
- Results from experience or practice
- Cannot be measured directly
- Produces relatively permanent changes in behavior
Training:
• Therapist gives patient a specific solution to the motor problem
Skill Acquisition
• Patient learns how to solve motor problem
• Investment Principle (Gordon Principle) James Gordon 1992
- Old strategy in deep well
- As learn, may regress in skill performance
- Over time practice gives new strategy which may be more efficient
Non-Associative Forms of Learning• Involve reflex pathways • Habituation is a decreased responsiveness that occurs as a result of repeated exposure to a non-painful stimulus • Sensitization is an increased responsiveness following a threatening or noxious stimulus • Sensitization counteracts habituationAssociative Forms of Learning• Through associative learning, a person learns to predict relationships - Classical conditioning consists of learning to pair two stimuli - Operant, or instrumental, conditioning is basically trial-and-error learning • Law of Effect: - Rewarded behaviors will be repeated - Discouraged behaviors will notClassical ConditioningBefore learning: • Conditioned Stimulus -> No response • UnConditioned Stimulus -> UnConditioned Response After learning • Conditioned Stimulus -> Conditioned Response (formerly UCR) Note: learning is most likely to occur in environments that are relative and meaningful to patientProcedural Learning• Learning tasks that can be performed automatically without attention or conscious thought • Develops slowly through repetition of an act over many trials • Learning occurs in the striatum of the basal ganglia • Generally does not require higher levelsDeclarative or Explicit Learning• Knowledge that can be consciously recalled • Involves the ability to remember factual knowledge • Requires the ability to verbally express the process to be performed • Learning occurs in the medial temporal lobe areas, hippocampus, and subiculum • Requires processes such as awareness, attention, and reflection • Advantage is that it can be practiced in ways other thanthe one in which it was learned • Is episodic-life events AND semantic-words, ideas, conceptsExplicit Learning Types of Processing1) Encoding 2) Consolidation 3) Storage 4) RetrievalEncoding• The process by which information is initially recorded in a form usable to memory • Involves the neural circuitry and requires attention • Is determined by the level of motivation • Extent of attention to information • Ability to associate it meaningfully with info already stored in memoryConsolidation• Process of making information stable for long term memory storage • Involves structural changes in neuronsStorage• Long term retention of memories • Has vast capacity as compared to short term memories • Working memory requires attention to the taskRetrieval• The recall of information from different long-term storage sites • Is subject to distortion • Most accurate when retrieved in the same context in which it was createdWorking Memory or Short Term Memory• Is critical for encoding and recall of LT memory • Consists of: - Attentional control system (prefrontal cortex) - 2 Rehearsal Systems (located in different parts of the posterior parietal or visual association cortex) 1) Articulatory loop-rehearsing language 2) Visuospatial sketch pad for vision and actionTheories of Motor Learning• A group of abstract ideas about the nature and control of the acquisition or modification of movement • Based on current knowledge regarding the structure and function of the nervous system • Are part of the foundation for evidence based practiceAdam's Closed-Loop Theory (1971)• Sensory feedback used for the ongoing production of skilled movement • Memory trace used in the selection and initiation of the movement • Perceptual trace built up over a period of practice and becomes the internal reference of correctnessAdam's Closed-Loop Theory Implications• It is essential to have the patient practice the same exact movement repeatedly, to one accurate end point • The more time spent practicing the movement as accurately as possible, the better the learning will be • Errors produced during learning increase the strength of an incorrect perceptual traceAdam's Closed-Loop Theory Limitations• The theory cannot explain the accurate performance of novel movements or open-loop movements made in the absence of sensory feedback • It may be impossible for the brain to store a separate perceptual trace for every movement ever performed (storage problem) • Variability in movement practice may actually improve motor performance of the taskSchmidt's Schema Theory• Learning a motor pattern - 4 things stored briefly in ST memory 1) Initial movement conditions, position of body in space 2) Parameters used in motor program (force/speed) 3) Outcome of movement - Knowledge of results (KR) - How did it feel? Was it correct? etc 4) Sensory consequences of the movement • Information stored as a recall schema and recognition schema • Schema: Generalized motor program contains the rules for creating the spatial and temporal patterns of muscle activity needed to carry out a given movement • Recall schema is used to select a specific response • Recognition schema is used to evaluate the responseSchmidt's Implications• Optimal learning will occur if a task is practiced under many different conditions • Affordance is the ability to alter a task in various environmental conditions • Sensory information informs rules/schema for performing that skillSchmidt's Limitiations• Differences between children and adults with variable forms of practice - Adults variable practice - mixed results - Kids variable practice - good results (no preset experiences or rules) • Lack of specificity of interaction with other systems during motor learning • Inability to account for the immediate acquisition of new types of coordination • Centipede that had all but 2 pairs of legs removed, immediately walked in quadrupedEcological Theory - Karl Newell 1991• Motor learning is a process that increases the coordination between perception and action consistent with the task and environmental constraints • The theory emphasizes dynamic exploratory activity of the perceptual/motor workspace to create optimal strategies for performing a task • Search strategies for movement decision • Perceptual information (perceptual cues) - Relates to understanding the goal of the task and the movements to be learned (demonstration) - Provides feedback (knowledge of performance (KP), and knowledge of results (KR)) - Used to structure the search for a perceptual motor solution appropriate to the task • Perceptual cues critical to task execution are "regulatory cues" (Gentile 1972)Ecological Theory Implications• The patient learns to distinguish the relevant perceptual cues important to organizing action • In reaching, size of glass, weight of glass, learn to recognize cues in the environmentEcological Theory Limitations• Still a very new theory • Interactions between the individual, task, & environment • Has not been applied to specific examples of motor skill acquisition in any systemic wayTheories Related to Stages of Learning• Focus on motor learning from a temporal (over time) perspective • Attempt to more carefully characterize the learning processFitts & Posner Three-Stage Model (1967)• *Cognitive Stage*: Person tried a variety of strategies, performance variable full of errors, but improvements large • *Associative Stage*: Person has selected best strategy for the task - internal reference for correctness, refinement • *Autonomous stage*: Minimal attention to performance, performance is stable, can devote attention to environmental factors, multi-taskFitts & Posner Later Stages of Motor Learning• Automated motor skills require less attention AND paying too much attention to the elements of the task may reduce performance • May be possible that focusing cognitive resources on a well learned task that has become automated interferes with the automatic motor control process (focusing on "deep well" task interferes with it)Fitts & Posner Clinical Implications• Can use this information as a guide for progression - Initially focus on attention - Allow practice so skill is refined - Add component to allow for automated motor control of taskSystems Three-Stage Model1) Novice: Freeze degrees of freedom, not most efficient, balance control 2) Advanced Stage: Begin to release the degrees of freedom, leads to more coordinated and efficient movement 3) Expert Stage: Now released all degrees of freedom to be the most efficient Ex: Skiing, snowboarding, ice-skatingSystems Three-Stage Model Clinical Implications• Explains coactivation of muscles during early stages of acquiring a new motor skill allowing for a reasonable solution to control the degrees of freedom • Offers new rationale for using developmental stages in rehab. Can view motor development using biomechanics as a gradual release of the degrees of freedom • Importance of external support for patients with coordination problems. Then systematically reduce supportGentile's Two-Stage ModelFirst Stage: Goal of the learner is to develop an understanding of the task dynamics Second Stage: Goal of the learner is to refine movement - Fixation/diversification stage - OKC vs CKCStages of Motor Program Formation• Hierarchical changes that may occur in movement control as motor programs are assembled during the learning of a new task • Learning to shift gears in a car - Early stages of practice, each components is in a separate motor program (Break down skill) - As learn components are grouped together - Late practice, becomes one programPractical Applications of Motor Learning• Different motor learning factors are important to consider when retraining patients with motor control problems • How can I maximize the learning for my patient? • What type of feedback should I give? • What type of practice schedule?Practice Levels• Most important factor in retraining motor skills • Rate of improvement during any part of practice is linearly related (on a log scale) to the amount left to improve • Baby walks 29 football fields per day when learning how to walk - Estimated 15 falls per hour; 10,000 falls during learning period • Constrained-reduced therapy helps via repetitionFeedback - All sensory information available as the result of movement• Intrinsic (inherent): Comes through various sensory systems, CNS (visual, somatosensory, etc) • Extrinsic (augmented): Enhanced - Concurrent: Given with the task, verbal or manual - Terminal: Given at the end of task about outcomeKnowledge of Results (KR)• Terminal feedback about the outcome of the movement, in terms of the movement's goal • Provides temporary effects on the subjects ability to perform a task • Number of trials to complete before giving KR varies depending on the task (if you do it less often, it might be more influential; if you give feedback 100% of the time they become dependent) - At least give results after every 5 reps • Precision varies for adults vs childrenOptimal KR• KR given on a fading schedule improves retention of skill • Immediate KR is detrimental to learning • Best number of trial to complete before giving KR varies with taskKnowledge of Performance (KP)• Feedback relating to movement pattern used to achieve goal • Most powerful form of feedback • Ex: "I like your quick arm reaching" or "it's good to push hard against the floor with your feet"Benefits of Feedback• Feedback can speed up the learning rate • Irrelevant feedback does not result in learning • Provides guidance by reporting errors • Helps motivate the patient • Keeps patient alert, trying harder • Give immediate feedback during acquisition • Give less feedback as they learn the skillPractice Conditions• Massed vs distributed practice • Constant vs variable practice • Random vs blocked practice: contextual interference - Blocked: one task at a time - Random: vary tasks - Variable practice: rotate tasks to be learned - Motivation: does the patient want to do the task?Massed vs Distributed Practice• Mass practice: amount of practice time in a trial is greater than the amount of rest time between trials - Need to watch out for fatigue or injury • Distributed practice: amount of rest between trials is equal to or greater than the amount of time for the trial • Which is better? - For continuous tasks, distributed practice - For discrete tasks, the evidence is unclearConstant vs Variable Practice• Constant practice: Practice is the same for each trial without variations (important for learning, but need to add variety) • Variable practice: Practice where an aspect of the task varies throughout each trial (important for learning task in different conditions) • Which is better? - Task dependent - Task requiring variable conditions are best practiced using variable practice - Tasks to be performed in constant conditions should be practiced that wayRandom vs. Blocked Practice• Blocked Practice: Practicing one task for a block of trials and then moving onto the next task • Random Trials: Practice different tasks in random order • Which is best? Performance is improved with randomly ordered conditions, but need to consider other factors - Skills that use different patterns of coordination - Characteristics of the individual - level of experience and intellectual abilitiesWhole vs Part Training• Part Training: Components of task defined in relation to the goals of the task - Task analysis - Processes of identifying the components of a skill or movement and then ordering them into a sequence - Patient practices each component in isolation then combines them into whole task • Whole training: Components must be practiced within overall context of the task • Effective if task can be naturally divided into unites that reflect inherent goalsTransfer• Amount of transfer depends on similarity bt 2 tasks or 2 environments • Critical aspect is similarity of neural processing demands in the 2 situationsMental Practice• Mental practice is an effective way to enhance learning during times when physical practice is not possible • Neural circuits underlying the motor programs for the movements are actually triggered during mental practiceGuidance vs. Discovery Learning• Guidance Learning: Learner is physically guided through the task to be learned - Should only be used at the outset of teaching a task • Discovery Learning: Learner is allowed to practice the task without guidanceChallenge Point Framework (CPF): A framework for optimizing motor learning• Theoretical framework for organizing the learning environment by taking into account: - Characteristics of the learner - skill level - Task being learned - difficulty of task - Environment - Defined by conditions of practice & feedback • These things determine the challenge point for learningCharacteristics of the Learner: Skill Level• What is the patient's present level of skill at the task? - If acute recovery stage: Low skill level, blocked practice with high KR may be best - As skill level improves - Random practice with low KRCharacteristics of the Task• *Nominal task difficulty* - Factors that are constant such as perceptual and motor processing requirements for the task - Invariant and inherent characteristics of the task • *Functional task difficulty* - Variable depending on skill level of performer and conditions under which the task is being performed or practicedCharacteristics of the Environment• Organization of the learning environment - Conditions of practice and feedback - Can be manipulated by therapistRecovery of Function• The reacquisition of movement skills lost through injuryConcepts Related to Recovery of Function• Definitions for function and recovery • Recovery vs compensation • Sparing of function - when function is not lost • Stages of recovery - Spontaneous recovery - Forced recoveryFunction• Complex activity of the whole organismRecoveryRegaining the function after injury - Achieve functional goal in the same way as before the injury - Achieve task goals with effective and efficient meansRecovery vs Compensation• Compensation: Behavioral substitution or alternative behavioral strategies are adopted to complete the task - "Should therapy be directed at recovery of function or compensation"Sparing of FunctionWhen function is not lost despite injuryDefining Neural Plasticity• Plasticity: General term describing ability to show modification • Neural plasticity: A continuum from short-term changes in synaptic connections among neurons • Shift from ST to LT learning reflects a move along the continuum of neural modifiabiltyPlasticity & Learning• Many factors modify synaptic connections • Learning changes - Effectiveness of neural pathways - Anatomic connections of neural pathwaysComplex Forms of Motor Learning• Repeated practice of a motor skill results in improved synaptic efficiency between the sensory and motor cortex • The efficiency of the thalamic input to the motor cortex is facilitated with repeated practice • The somatosensory cortex participates in the learning of motor skills, through long-term potential (LTP), and after learning, other areas (such as the thalamus) may take overInjury-Induced Plasticity & Recovery of Function• The brain is not structurally static but continuously changes in structure and function - Intercellular (changes at the synaptic level) - Network (cortical reorganization) levels • Restorative (direct) mechanisms of recovery of function • Compensatory (indirect) mechanisms of recovery of functionPhysiology of Recovery• Restorative-Direct: Resolution of temporary changes and recovery of the neural tissue itself • Compensatory-Indirect: Completely different neural circuits enable recovery of lost or impaired functionEarly Transient Events that Depress Brain Function• Diaschisis - transient CNS disorder involving loss of function in a structural intact brain area because of loss of input from an anatomically connected injured area of the brain • Edema follows brain injury - Cytotoxic: accumulation of intracellular fluid - Vasogenic: leakage of proteins and fluid from damaged blood vesselsChanges in Cortical Maps After Lesions During Recovery• Cortical representation of the body is continuously modified in healthy adults in response to activity, behavior, and skill acquisition • Cortical reorganization occurs after a peripheral injury or CNS injuryRemapping Following Peripheral Lesions• Neighboring maps expand their receptive fields to cover much of a denervated region • Reactivation of the cortex is due to increased responsiveness of weak inputs from neighboring areas; if denervation exceeds a certain distance, silent areas remain • Reorganization of somatosensory and motor sensory systems occurs following peripheral nerve lesions or amputationRemapping Following Central Lesions• Damage to central neural structures also results in alterations to cortical maps and changes in neural activation patterns • Focal damage to the CNS can increase the capacity for structural and functional changes within the CNSReorganization of the Affected Hemisphere during Recovery of Function• Motor recovery may be mediated by other cortical areas in the damaged hemispheres - Redundant pathways - New regions • Primary motor cortex lesions result in activation of secondary motor areas - Premotor and supplementary motor cortex - Cingulate cortexContributions of Ipsilateral (Uncrossed) Motor Pathways to Recovery of Function• Uncrossed pathways play an important role in recovery of function • The contralesional primary motor cortex may play a roleCerebellar Contributions to Recovery from Cortical Injury• The role of the CBL in recovery of function may be related to its role in motor learning • New cerebellar cortical synapses are associated with complex skill learning but not with gross motor activation in the absence of learningCross-Modality Plasticity• When deprived of its usual input, the part of the cortex normally responsive to that input may be responsive to inputs from other sensory modalities • Sensory inputs from one modality can activate cortical areas of other modalities • New connections are functional, but have abnormalitiesEffect of Training• Reorganization in somatosensory cortex resulting from training • Optimal timing and intensity of training to maximize neural plasticity • Cortical stimulation used to facilitate motor recoveryClinical Implications of Recovery• Increased understanding of some of the neural changes that occur following injury • Evidence that experience is very important in shaping cortical mapsStages of Recovery• Spontaneous Recovery: Recovery without specific interventions • Forced Recovery: Obtained through specific interventions designed to impact neural mechanismsFactors Affecting Recovery of Function1) Endogenous (within the individual) factors 2) Exogenous (external to the individual) factors 3) Pre-injury factors 4) Post-injury factorsPre-Injury Neuroprotective Factors / Endogenous (within the individual) factors• Brain trophic factors • Gender • Weight • Premorbid factors • Age • Lesion factors (size, speed) • Genetic factorsExogenous (external to the individual) factors• Pre-injury factors - Exercise - Environmental enrichment - Dietary restriction • Post-injury factors - Pharmacologic treatment - Neurotrophic factors - Effects of Exercise & TrainingPost-Injury Factors*Effect of Pharmacology* • Use of drugs that reduce the NS's reaction to injury and promote function - Affect trophic factors, promoting regeneration & cell survival - Replace neurotransmitters lost because of cell death - Prevent effects of toxic substances produced by or released by dead/dying cells - Restore blood circulation - Antioxidants which block the effect of free radicals that destroy cell membranes (Vit E) *Neurotrophic Factors* - Insulin like growth factor - modulate synaptic efficacy by regulating synapse formation, NT release, and neuronal excitability and thus may increase neuroplasticity - Brain-derived neurotrophic factor (BDNF) has been shown to have an impact on neuroplasticity *Effects of Exercise & Training* - CIT - Timing & intensity of interventionEffect of Age• The brain reacts differently to injury at different stages of developmentCharacteristics of the Lesion• Fairly strong relationship between injury severity & long-term functional outcomes • Considerable variability in recovery even among individuals with severe brain injuryImplications of Motor Learning for PT• Use a goal developed by the patient • ID/Break down tasks to be learned • Rotate tasks to be learned • Intersperse other activities to enhance registration • Use block schedule for early practice • Practice should be at level of emerging skill • Random, variable practice will increase long term motor learning • Variability in skill in differing environments