54 terms

Motor Control Theories

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Theory
general explanation of how something works
- cannot be tested per say
Hypotheses
specific statements about the relationships between 2+ variables, deduced from a more general theory
- can be tested thru collection of data
Hypothesis orientated algorithm for clinicians (HOAC)
- PTs examination strategy is based on hypotheses regarding the nature of the problem
- PT tests and refines his/her hypotheses based on the outcome of the examination
- PT plans intervention strategy based on the refined hypotheses
Theory of human motor control
- human motor control is complex and multidimensional
- not a unified theory of motor control
6 Motor Control Theories that have most influenced PT management of patients with CNS dysfunction
- reflex theory
- hierarchical theory
- motor programming theory
- bernstein's systems theory
- ecological theory
- dynamic systems theory
Reflex theory
movements are reflex responses to stimuli
Clinical application of reflex theory
- some patients reflexes seem to have a substantial impact on functional movement
Evaluation based on reflex theory
- eval consists of identifying what sensory inputs result in what motor outputs, and how each stim- response relationship impacts on function
Interventions based on reflex theory
- using sensory input to achieve desired outputs
- eliminating sensory inputs resulting in undesired outputs
Manipulating sensory inputs to improve function example
- tonic labyrinthine reflex (stim -> response)
- head in relative supine -> increases extensor tone across neck, trunk, and extremities
- head in relative prone -> increases flexor tone across neck trunk and extremities
If there is a strong primitive reflex usually means
not good motor control
Limitations of Reflex Theory
doesnt explain: how people can produce movements spontaneously, wihtout any change in sensory input, how diff responses can result from the same stim
Hierarchical Theory
- control of movement occurs from the top down
- in a healthy org, motor control system is a bureaucracy in which each level must take orders from the level just above it, and ultimately the highest level of the CNS controls what movement occurs
Damage to CNS...
releases control over lower levels and thats why we see primitive reflexes in patients with CNS dysfunction
Neuromaturational Theory (hierarchical developmental theory)
- normal sequence of motor development occurs as a consequence of progressively higher levels of the CNS maturing and gaining control over the lower reflex levels
Cortex controls?
- equilibrium reactions
- bipedal function
Midbrain controls?
- righting reactions
- quadrupedal function
Brainstem spinal cord
- primitive reflex
- apedal function
Tx of pts with developmental delay or adults with brain damage
Should follow developmental sequence, highest level of motor control is dependent on the function of the intermediate level which suppresses the primitive reflex level
Early versions of NDT...
tried to suppress primitive reflexes and stim postural control following the developmental sequence
In traditional NDT, if your patient didnt have adequate righting and equilibrium rx to have good sitting balance...
you would not work on standing activity, you would spend your tx time working on equilibrium and righting rx with the pt sitting or quadruped
Limitation of Hierarchical theory
- doesnt explain why sometimes health individuals control of motor output is dominated by lower levels
- examples: hot pain, some kids learn to walk before they can crawl
Motor Programming Theory
movement patterns or rules of action are stored in the CNS as motor programs and can either be triggered by sensory input or initiated centrally
- addresses some of the limitations of the reflex theory - explains how movements can occur in the absence of sensory input and allows for spontaneous and voluntary movements
Stereotyped movement patterns suggested...
there are central pattern generators in the CNS
Variety of Types of Motor Programs
- motor programs can:
- motor programs can be:
- exist in the organism at birth, such as CPGs or can be learned, such as postural strategies or handwriting
- specific to particular muscles or more abstract relationships between antagonistic movements
Evaluation should include a determination of what programs are...
intact and what motor programs need to be taught, re-taught or compensated for
Motor Program Theory: Intervention invovles
teaching the pt new motor programs or teaching the pt to apply surviving motor programs to perform desired activities
Examples for using motor program theory:
- if patient does not use an ankle strategy
- if a patient who had a stroke can only move the arm in a flexor synergy
- teach the pt to perform this motor program
- teach him a variety of other motor programs
Limitations of Motor Programming Theory
motor programs stored in the CNS cannot take into account variations in the amount of muscle activation needed when the muscle is positioned against gravity vs gravity eliminated and when a muscle is weak due to fatigue
Bernstein's Systems Theory. He recognized...
Recognized the CNS is not the only thing involved in determining the motor output of the organism. Recognized that the human body is a physical subject to physical laws such as gravity, inertia, and friction, and that motor output is a function of many factors, including biomechanical features of the body
Bernstein's Systems Theory
- what type of model? and description
- distributed (as opposed to hierarchical) model of motor control: control of movement is distributed throughout many interacting systems working cooperatively to achieve movement
Bernstein's Systems Theory
- synergies...
exist to simplify the problem of controlling the many degrees of freedom in the body -> not necessarily bad but it is all they can do
Clinical application of Bernstein's Systems Theory- it reminded neurological therapists...
- sometimes mechanical limitations, rather than primitive reflexes, were causing patients' problems with movements
Bernstein's Systems Theory.. Evaluations must consider
biomechanical aspects of human movement as well as neurological control issues, and identify which aspects are the limiting factor for each patient problem
Interventions (using Bernstein's Systems Theory )
- address biomechanical constraints: increase flexibility (stretching) and increase ability of muscles to generate force (strengthening)
- address learning movement combos (synergies) that occur in functional activities
Limitations of Bernstein's Systems Theory
- more comprehensive than previous
- fails to consider cognitive and perceptual aspects of how the organism interacts with the environment
Ecological theory
- motor control evolved to enable organisms to interact with their environments in order to perform goal-oriented behavior
Affordance
an opportunity for action that the environment offers to the organism (living thing)
- the concept of affordances takes into account characteristics of the organsim as well as characteristics of the environment
How we perceive affordances is
learned through our own interaction with the environment or through the experience of others that is shared with us
Characteristics of the environment are only meaningful in so far as they
enable or prevent desired actions
Perception is
our interpretation of the meaning of our sensations
Movement in the environment allows the
individual to translate meaningless sensory input (eg color and light) into meaningful perception (objects and surfaces)
Therapists must
- eval pt's ability to perceive the relevant features of the environment
- provide intervention to facilitate pts perception
- eval the extent to which a pt is interpreting the environment in a way that enables the pt to be successful at goal-oriented behavior
Limitations of ecological theory
focuses on the person/environment interface, but doesnt address other aspects of neuromotor control
Dynamic systems theory of motor control
merging of dynamical action theory with bernstein's systems theory to address two critical features of motor control
- it is a complex system in which there are many interactive subcomponents
- it is a dynamic system which means it changes over time
Dynamic systems theory
- complex systems have many subcomponents that interact. interaction among these subcomponents takes the system to a new state that cannot be explained through reduction to the subcomponents
- new states/new patterns emerge through the interaction of multiple subcomponents
- no need for a higher center issuing commands to achieve coordinated action
the change from one sate to another is referred to
as a phase shift or transition;
the phase shift/transition is a
nonlinear change - movement pattern is not directly proportional to the change in velocity
clinical example of this phase shift/transition
the change from doing one step at a time to step over step
Control parameter
- is
- examples
- subcomponent of the complex system that if changed results in the emergence of a new state
- ex: shift from walking to trotting to galloping, velocity = control parameter
- may be linear but doesnt have to be
Stability and instability in the system is measured
in terms of variability in the state of the system (stability is not talking about balance)
A pertubation to the system could cause
a stable state to transition to an unstable state which = instability of the system (variability) which a patient needs to be in to have an effective change
Clinical implications intervention for dynamic systems theory
- intervene in a functional context. Motor behavior emerges within the context of the person actively engaging in performing a task unnecessary to follow developmental sequence
- manipulate control parameters to enable patients to achieve desired movements
Limitations of Dynamic SystemsTheory
does not describe the details about how the nervous system and the body work that help us hypothesize likely control parameters -> details of interventions would be a matter of trial and error