Week 11b: Motor Control Theory- Overview and History

motor control theory

describes and explains how the nervous system coordinates movement to successfully perform a variety of motor skills in a variety of environments- is a framework for interpreting behavior, and helps generate new hypothesis for how movement occurs- guides clinical practice and working hypothesis to understand our examination and treatment

coordination

the patterning of the head, body, and limb movements relative to the patterning of environmental objects and events- two important considerations refers to the relationship among the head, body, and/or limbs at a specific point in time during the s skill performance, relation to the context in which the skill is performed

degrees of freedom problem 

number of independent components in a control system and the number of way each component can vary, How to design a complex system that must produce a specific result? 

the actual number of DoF to control depends on which level of control we are considering (motor unit vs joint)

open loop and closed loop control systems 

different ways in which central and peripheral NS initiate and control action, both involved the movement control center (executive) which generate and sends instruction to effectors 

open-loop control system

uses feedback, the control center gives enough information for the effectors to initiate movement and needs feedback to continue and end movement, this enables learning

closed loop control system

no feedback, complete instructions to the effectors to perform the planned movement

evolution of motor control theories

• early 1900s: reflex and hierarchal theories

• 1960-1970s: motor programming theories

• 1960-present: ecological theory

• 1970-1980s: systems and dynamic systems theories

reflex theory

from 1906, prevailed for the next 50 years- suggested reflex as the building blocks of all movement- stimulus causes the response as sensory input dictates motor output. As CNS developed/matured, the reflexes are inhibited and/or integrated into more functional postural and voluntary motor responses

weakness of the reflex theory

doesn’t explain well spontaneous movement and movement without sensory stimulus, very fast movements that occur quicker than the summation of a group of reflexes, and varying responses to the same stimulus being possible

clinical implication of the reflex theory

reducing spasticity can enhance normal movement patterns by decreasing the abnormal reflexive response

hierarchical theory 

was developed to explain the shortcomings of the reflex theory, suggests top-down control in which higher centers control adn inhibit lower centers (cortex > midbrain > brainstem > spinal cord), and that the brain shows neuromaturation in which it inhibits unnecessary reflexes, allowing for the desired ones, and if higher levels are damaged then lower level reflexes will only be restored once higher center control center is 

gaps in the hierarchical theory

control of the brain is not purely top-down, all CNS levels can influence other levels depending on the task

clinical relevance of the hierarchical theory

led to the Brunnstrom adn Bobath methods (early physical therapists), and disorders of higher centers leads to re-emergence of abnormal reflex patterns (spasticity, etc)

information learned from early movement theories (reflex and hierarchical)

• use to predict function: during the examination we text reflexes to predict whether the system is intact or not

• use to interpret movement behaviors: movement behaviors can be interpreted in terms of the presence or absence of controlled reflexes, synergistic patterns

• use to help explain abnormal motor behaviors in people with CNS damage: motor dysfunctions after neurological injury are due to interruptions in the higher center’s ability to control lower centers

early motor control theories impact on clinical practice 

clinical approaches relied on examination of reflexive behavior, treatments based on inhibition or facilitation of abnormal postural reflex activity, optimal sensory input needed for stimulating normal motor output 

motor programming theories

shift in belief that the CNS is not just a stimulus-response, reactive system, is a memory based construct that controls coordinated movement

Schmidt’s Schema theory

solves the DoF problem through an executive control operation that organizes motor programs and schema (a rule or set of rules that serves to provide the basis for a decision)

control components for learning and control of skills 

generalized motor program and motor response schema 

generalized motor program

control mechanism responsible for controlling movement coordination patterns of classes of actions

motor response schema

specific rules governing performance of a skill in a given situation (parameters for the GMP)

schmidt’s generalize motor program 

the memory representation of a class of action that share common invariant characteristics

invariant features

these features are the signature of a GMP and form the basis of what is stored in memory, characteristics that do not vary across performances of a sill within class of actions

parameters 

movement related features of the performances of an action that can be varied between performances 

motor program theory

variability in motor control considered consequence of errors in motor performance, error considered bad (performance improves when error and variability decreased), allows for movements to occur without reliance on sensory feedback (central pattern generators- examples is rhythmic pattern generator)

strengths of motor programming theories

there is an emphasis on practice, feedback, and memory

limitations of motor programing theories 

storage capacity problem, fails to account for benefits to varying practice conditions enhancing motor learning, doesn’t account for variables within the environment or neuromusculoskeletal system 

systems theory

perspective shift from the motor programming theories, whole-body approach and distributed motor control, holistic movement understanding,