Theories of Motor Control Flashcards
Main Theories of Motor Control
- Reflex Theory
- Hierarchical Theory
- Generalized Motor Programs
- Dynamic Systems
Reflex Theory
- Reflexes are building blocks of complex behavior
- Reflexes are located at the spinal level with no cerebral influence
- Bottom –> up
The Central Pattern Generator
- Neuronal networks within the spinal cord generate rhythmic activity (walking, stepping, grooming)
- Hard-wired
Empirical Evidence of CPG
- Spinal and decerebrate cat preparations
- Babies initial stepping response
- Spinal cord lesions in adult humans
Reflex Theory Implications
- Should allow practitioners/ therapists to predict function
- Movement behaviors interpreted in terms of the presence or absence of controlling reflexes
- Focus on enhancing or reducing the effect of various reflexes during motor tasks
What are the possible limitations of reflex theory?
- Does not explain action in the absence of feedback
- Does not explain fast movements
- Does not explain how one single stimulus results in varying responses
- Does not explain ability to produce novel and combined movements
Hierarchical Theory
- Lower reflexes are only present when higher cortical structures are damages
- Organizational control of motor system is top –> down
- Each higher center can modulate the one below, not bottom –> up control
Evidence for Hierarchical Theory
- Development
- Infants begin life with certain reflexes that disappear as they mature
- Attributed to increasing corticalization of the CNS
Neuromaturational Theory
As we grow (6 months) all reflexes should disappear
Limitations of Hierarchical Theory
- Theory minimizes musculoskeletal changes
- Cannot explain bottom –> up control (reflexes)
- Reflexes that govern lower control in adults are critical in postural control and adaptive location
Motor Program Theories
- Generalized schemata of action which determines the sequence of specific actions
- Cognitive structures responsible for skilled movements
- A procedural memory comprised of the rules commanding muscular activity for producing specific skills
Evidence of Motor Programs through Deafferentation Studies
Movement patterns are still present in the absence of sensory feedback
Cognitive-Based Theories
Broad view:
- Centrally located (CNS)
- Hierarchical arrangement of elements
- Heavily sensory feedback dependent at first
- Sufficient to explain learning and control of movement skills
Information Processing Model
- Describes cognitive processes associated with working of motor programs
- Sensory info –> Perceptual stage –> Decision-making stage –> Programming stage –> Response output
Perceptual Stage
- Sensory info flows in from external and internal environments
- CNS selects the most important input sources
- Difference between sensation and perception
Sensation vs Perception
- Sensation: the process of sensing our environment through touch, taste, sight, sound, and smell
- Perception: the way we interpret these sensations and therefore make sense of everything around us
Decision-Making Stage
Decide on a course of action
Programming Stage
- Preparing appropriate motor program to carry out the action
- Appropriate motor program retrieved
- Posture changes made
- Timing of muscle activation prepared
- Sensory systems oriented (focal vision)
- Action initiated when appropriate
Closed-Loop Systems
- Dependent on feedback
- No action until feedback says so
- Slow and deliberate movements
- Corrections can be made as the movement progresses
Advantages of Closed-Loop Systems
- Appropriate with performing unpracticed skills
- Movements can be corrected while they are being made
- More precise and accurate movements
Disadvantages of Closed-Loop Systems
- Demands a lot of attention
- Too time consuming
Adams’ Closed-Loop Theory
- Formation and strengthening of neural traces
- Select and initiate desired action based on a memory trace
- Evaluate correctness of action executed based on perceptual trace
Specificity of Practice Hypothesis
The best learning experiences are those that most closely approximate the movement components and environmental conditions of the target skill and target context
Problems with Adams’ Closed-Loop Theory
- Novelty Problem
- Storage Problem
Novelty Problem
- How is a specific motor act performed for the first time?
- Since the memory trace does not exist yet, there is nothing to initiate the action
Storage Problem
A specific neural tract would have to be stored for each unique scenario
Schmidt’s Schema Theory
- Motor programs are general in nature, more adaptable
- Generalized Motor Programs (GMP) have certain invariant and variant features
Invariant Features of a GMP
- Sequencing
- Relative timing
- Relative force
Sequencing of a GMP
Program is written in the same sequence each time
Relative Timing of a GMP
Time for each unique segment stays constant
Relative Force of a GMP
EMG activity remains constant
Variant Features of a GMP
- Overall duration
- Overall force
- Muscle selection
Overall Duration of a GMP
Time to complete the movement can be altered
Overall Force of a GMP
We can increase or decrease the size of the movement
Muscle Selection of a GMP
Different muscles can activate to accomplish a task
Schema Learning
- Post-response evaluation???
Variability of Practice Hypothesis
- Learning is the greatest when one performs the
skill in a variety of ways and/or contexts rather
than one way and/or one context - Greater information is available for abstracting relationships
- Adapts GMP for different situations
Open-Loop Systems
- No monitoring of feedback
- Motor program holds all information needed for execution of response
- Motor programs are prestructured to a particular environmental condition through feedback
- Feedforward, not feedback
Advantages of Open-Loop Systems
- Quicker movements (prestructured)
- Greater amount of attention available for other tasks
Disadvantages of Open-Loop Systems
- Not appropriate for unpracticed skills
- Not adaptable
Motor Program Theories Limitations
Does not take into account that the nervous system must deal with both musculoskeletal and environmental variables in movement control
Dynamic Systems Theory
- Coordination of movement is the process of mastering the redundant degrees of freedom of the moving organism
- A motor behavior’s stability is associated with a self-organizing system
- Takes the influence of biomechanics and external forces into account
- Synergies make possible almost the whole variety of movements
Synergies
- Organize task sharing among muscles
- Allow co-variation among muscles working together to accomplish a goal
Principle of Abundance
- Synergies increase the stability and flexibility of the motor system
- A single task can be done with multiple commands
5 Basic Assumptions of Dynamic Systems Theory
- Self-Organization
- Attractor states
- Nonlinear changes
- Control parameters
- Order parameters
(First 3 are the most important)
Self-Organization
Individual parts naturally organize into an ordered pattern
Attractor States
The preferred patterns of movement
Nonlinear Changes
Changes (such as from a walk, to a jog, to a sprint) can be abrupt
Control Parameters
- Velocity
- How new patterns emerge
- Reciprocal extension/flexion of index fingers alternate at slow speeds but symmetrical at fast speeds
Order Parameters
Changes in movement are difficult (unstable) or easy (stable)
Implications of the Dynamic Systems Theory
- Stresses the importance of understanding the body as a mechanical system
- Not just the action of the nervous system but the nervous system as filtered by the body
- Examination and intervention must focus not only on issues within individual systems, but the effect of the interaction among multiple systems
Limitations of the Dynamic Systems Theory
- Assumes the nervous system has a fairly unimportant role
- Assumes that the relationship between the physical system of the animal and its external environment primarily determine behavior
Neural Crosstalk
- Makes it hard to do opposite movements with opposite limbs
