PTP 512Neuroscience in Physical Therapy

Motor Control: Issues and Theories

Min H. Huang, PT, PhD, NCS

Objectives

• Identify individual, task, and environmental movement constraints

• Compare and contrast contemporary motor control theories

• Compare and contrast neurologic rehabilitation approaches with respect to assumptions underlying normal and abnormal movement control, recovery of function, and clinical practices.

Reflection……

• What is a theory?• What is the value of theory to clinical

practice?

HOW DOES MOVEMENT EMERGE?

Movement Emerges from the Interaction between Task, Individual, Environment

Environmental Constraintson Movement

• Regulatory–Essential elements that

determine the movement, e.g. chair height

• Non-regulatory–Feature that are not

essential but may affect the performance, e.g. background noise

Individual Constraints on Movement

• Action–“goal-directed”

movements• Perception

–Sensory integration• Cognition

–Mental functions underlying the establishment of a goal

Task Constraints on Movement• The nature of tasks determine

the movement required.• Classify tasks by

–Functional category, e.g. gait, bed-mobility, transfer

–Discrete (definite ending) vs. continuous (no end point), e.g. grasping vs. walking

–Stable vs. mobility, e.g. sitting vs. walking

Gentile’s Taxonomy for Task Classification

M: manipulation, Variability: inter-trial variability+ present, – absent

Gentile’s Taxonomy for Task Classification

 c

Body Stability Body Transport– M + M – M + M

Closed predictable environment– Variability        + Variability        

Open unpredictable environment– Variability        + Variability        M: manipulation, Variability: inter-trial variability

+ present, – absent

MOTOR CONTROL THEORIES – A TOUR THROUGH HISTORY

Discuss at your table group1) What did the therapist do?2) What did the patient do? How did the

patient perform the tasks?http://www.youtube.com/watch?v=mCiBehv_FOw&feature=related

http://www.youtube.com/watch?v=r5o5S-9zGpE

Reflex Theory

Reflexes are the building blocks of complex motor behaviors or movements

Reflex Theory• Sir Charles Sherrington, the integrative

action of the nervous system (1906) –Reflex chaining: complex movements are

a sequence of reflexes elicited together• This is based on the observation that

monkeys were unable to their arm after resection of one side of dorsal root ganglia. Therefore, sensory inputs must be essential in initiating movements.

Limitations of Reflex Theory

• Unable to explain–Spontaneous and voluntary movements–Movement can occur without a sensory

stimulus–Fast sequential movements, e.g. typing –A single stimulus can trigger various

responses (reflexes can be modulated) –Novel movements can be carried out.

Limitations of Reflex Theory• Taub demonstrated that monkeys with

bilateral deafferentation were able to move the arms. If with unilateral deafferentation, the monkey relearned moving the affected arm when the good arm was “constrained” in a sling. His findings lead to the constraint-induced movement therapy.

Stroke Rehabilitation: Constrained-Induced Movement Therapyhttp://www.youtube.com/watch?v=MMTh2hWvB2gTaub Therapy Clinic: Constrained-Induced Movement Therapy

Hierarchical Theory

Hierarchical Theory• Higher centers are always in control of lower

centers• Higher centers inhibit the reflexes controlled

by lower centers• Reflexes controlled by lower centers are

present only when higher centers are damaged

• Neuromaturational theory of development–The brain determines infant behavior!

Hierarchical Theory

Hierarchical Theory

• Based on the observation of motor development in children and adults–A child’s capacity to sit, stand, and walk

is related to the progressive emergence and disappearance of reflexes

–Brain stem reflexes (associated with head control) emerge before midbrain reflexes (associated with trunk control)

Current Concepts Related to Hierarchical Theory

• Each level of the motor system can act on other levels

• Reflexes are one of many processes of motor control

Clinical Implications of Hierarchical Theory

“When the influence of higher centers is temporarily or permanently interfered with, normal reflexes become exaggerated and so called pathological reflexes appear” …Brunnstrom, 1970

“The release of motor responses integrated at lower levels from restraining, influences of higher center, especially that of the cortex, leads to abnormal postural reflex activity”…Bobath, 1965

Limitations of Hierarchical Theory

• Environment and other non-CNS factors can affect movement, e.g. Thelen’s experiments showed that baby’s stepping response re-emerges with body weight support

• Normal adults exhibit lower level reflexes, e.g. flexor withdrawal

Body Sense. Scientific America Frontier. (1:00-2:40, 5:10-7:30)http://vsx.onstreammedia.com/vsx/pbssaf/search/PBSPlayer?assetId=68932&ccstart=235620&pt=0&preview=undefined&entire=yes

• Concept of a central motor pattern or motor program–Many studies found that movement is

possible even in the absence of stimuli or sensory input

–Sensory inputs are not required to produce a movement but they are important in adapting and modulating the movement

Motor Programming Theories

General setup for studies of locomotion in cats with spinal lesions

Rossignol, 2011

Central Pattern Generator (CPGs)

Rossignol, 2011

F flexor motoneurons E extensor motoneuronsDC dorsal columnsDRG dorsal root ganglion

Evidence of a Motor Program:Central Pattern Generator (CPGs)

• CPGs are spinal networks capable of generating bilateral rhythmic movements, such as swimming or walking, in the absence of descending and sensory inputs

• CPGs are network of interneurons that alternatively activate flexors and extensors on one side, and coordinate with CPGs on the other side

Motor Programming Theories

• Motor programs are–Hardwired and stereotyped neural

connections such as central pattern generators (CPGs)

–Abstract rules for generating movements at the higher level

• Motor program can be activated by sensory stimuli or by central processes

Writing

Motor Programming Theories

Limitations of Motor Programming Theories

• Does not consider that the nervous system must deal with both musculoskeletal and environmental variables to produce movements–e.g. identical neural commands to elbow

flexors can produce different movements depending on the initial position of the arm and the force of gravity

Clinical Implications of Motor Programming Theories

• Movement problems are caused by abnormal CPGs or higher level motor programs

• It is important to help patients relearn the correct rules for action

• Focus on retraining movements that are critical to a functional task, not just specific muscles in isolation

Systems Theory: Bernstein’s Degree of Freedom Problem

• How does the CNS select a solution from an infinite number of possibilities for a task?

• Solution–Higher levels activate lower levels while

lower levels activate synergies, i.e. groups of muscles that are constrained to act together as a unit

Systems Theory: Bernstein’s Degree of Freedom Problem

• Viewed body as a mechanical system, involving the interaction between mass, external force (e.g. gravity), internal force

• “Coordination of movement is the process of mastering the redundant degrees of freedom of the moving organism” (Bernstein, 1967)

Systems Theory: Latash’s Principle of Abundance

• Synergy is a task-specific covariation of elemental variables with the purpose to stabilize a performance variable, i.e. minimize errors of a performance variable –Reaching: joint rotation angle stabilize

hand position –Grasping: individual finger force stabilize

total grasp force–Standing stability: postural muscle activation stabilize COP

Systems Theory: Latash’s Principle of Abundance

• A muscle belongs to more than one synergy. Within a synergy, each muscle has a unique weighting factor that specifies the level of activation of that muscle within that synergy.

• Synergies assure small variability of the performance variable while allowing relatively large variability of each elemental variable

Postural perturbation study: each muscle may be activated to a different degree by each muscle synergy

Ting, 2005

Dynamic Systems Theory: Principle of Self-Organization

• Movement emerges as a result of interacting elements. No needs for specific neural commands or motor programs.

• Variability of movement is normal. Optimal amount of variability allows for flexible, adaptive strategies to meet the environmental demand

Dynamic Systems Theory: Principle of Self-Organization

A new movement emerges when a control parameter reaches a critical value

Limitation of Systems Theory

• Nervous system is fairly unimportant• How do we apply mathematics and body

mechanics to clinical practice?

Clinical Implications of Systems Theory

• Body is a mechanical system. Consider musculoskeletal factors underlying a patient’s movement problem

• Changes in movements may not necessarily result from neural changes, e.g. faster vs. slow gait, speed during sit to stand

• Encourage the patient to explore variable movements

Ecological Theory: Gibson’s Perception-Action Coupling

• Action is specific to the task goal and the environment

• Perceptual information of the environmental factors relevant to the task goal is necessary to guide the action

• Limitations:–↓ emphasis on nervous system

Clinical Implications of Ecological Theory

• Individual is an active explorer of the environment for learning

• Individual discovers multiple ways to solve movement problems in environment

• Fundamental to the play-based therapy for pediatric patients

Baby Sense. Scientific America Frontier. (1:00-2:40, 5:10-7:30)http://vsx.onstreammedia.com/vsx/pbssaf/search/PBSPlayer?assetId=68932&ccstart=235620&pt=0&preview=undefined&entire=yes

Discuss at your table groupWhat are the assumptions of movement control underling each of these treatment approaches?

http://www.youtube.com/watch?v=mCiBehv_FOw&feature=related

http://www.youtube.com/watch?v=r5o5S-9zGpE

NEUROLOGIC REHABILITATION APPROACHES

Reflex

Contemporary task-oriented

Neurotherapeutic facilitation

Muscle reeducation

Hierarchical Systems

Motor control models

Neurologic rehabilitation models

Muscle Reeducation• Change function at

the level of muscle• Vera Carter, a

practitioner beginning her work with muscle treatment of polio patients in Australia in the early 1930’s

Kendall Historical Collection

Assumptions of Neurofacilitation Approaches

• Abnormal movement is a direct result of the neurologic lesion

• Inhibit abnormal movement patterns to facilitate the normal movement patterns will lead to the return of functional skills

• Repetition of normal movement patterns will automatically transfer to functional tasks

Reflex- and Hierarchical Based Neurofacilitation Approaches

• Brunnstrom, Rood, Proprioceptive neuromuscular facilitation (PNF), Bobath’s neurodevelopmental treatment (NDT)–Retraining motor control through

“techniques” to facilitate and/or inhibit different movement patterns

–e.g. PNF UE D1 Flexion/Extension http://davisplus.fadavis.com/kisner/Chapter06.cfm

Task-Oriented Approach (motor control of motor learning approach)

Task-Oriented Approach• Movement is organized around a behavioral

goal and is constrained by the environment• Patients learn by actively attempting to solve

the movement problem rather than by repetitively practicing normal patterns of movement.–e.g. RIC constraint-induced movement

therapy camp http://www.youtube.com/watch?v=NhLsh1SW4Ak

Moving forward“….currently available evidence of dose–response relationships in motor learning, time-dependency of neuronal and functional recovery, and task specificity of treatment effects….…the lack of evidence as well as major changes over time in our understanding of underlying mechanisms about stroke recovery, which do not concur with the obsolete and constantly changing assumptions used to explain the Bobath Concept…”Kollen, 2009