PTP 512 Neuroscience in Physical Therapy Motor Control: Issues and Theories

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PTP 512Neuroscience in Physical TherapyMotor
Control Issues and Theories

• Min H. Huang, PT, PhD, NCS

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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.

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Reflection

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

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How does movement emerge?
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Movement Emerges from the Interaction between
Task, Individual, Environment
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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

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Individual Constraints on Movement

• Action
• goal-directed movements
• Perception
• Sensory integration
• Cognition
• Mental functions underlying the establishment of
  a goal

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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

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Gentiles Taxonomy for Task Classification
M manipulation, Variability inter-trial
variability present, absent
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Gentiles Taxonomy for Task Classification
  c Body Stability Body Stability Body Transport Body Transport
  c M M M M
Closed predictable environment Closed predictable environment Closed predictable environment Closed predictable environment Closed predictable environment
Variability        
Variability        
Open unpredictable environment Open unpredictable environment Open unpredictable environment Open unpredictable environment Open unpredictable environment
Variability        
Variability        
M manipulation, Variability inter-trial
variability present, absent
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Motor control theories a tour through history
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Discuss at your table group

1. What did the therapist do?
2. What did the patient do? How did the patient
   perform the tasks?

http//www.youtube.com/watch?vmCiBehv_FOwfeature
related
http//www.youtube.com/watch?vr5o5S-9zGpE
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Reflex Theory
Reflexes are the building blocks of complex motor
behaviors or movements
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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.

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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.

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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 Therapy http//www.youtube.com/watch?vMM
Th2hWvB2g Taub Therapy Clinic Constrained-Induced
Movement Therapy
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Hierarchical Theory
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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!

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Hierarchical Theory
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Hierarchical Theory

• Based on the observation of motor development in
  children and adults
• A childs 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)

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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

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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
  activityBobath, 1965

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Limitations of Hierarchical Theory

• Environment and other non-CNS factors can affect
  movement, e.g. Thelens experiments showed that
  babys stepping response re-emerges with body
  weight support
• Normal adults exhibit lower level reflexes, e.g.
  flexor withdrawal

Body Sense. Scientific America Frontier.
(100-240, 510-730) http//vsx.onstreammedia.co
m/vsx/pbssaf/search/PBSPlayer?assetId68932ccstar
t235620pt0previewundefinedentireyes
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Motor Programming Theories

• 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

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General setup for studies of locomotion in cats
with spinal lesions
Rossignol, 2011
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Central Pattern Generator (CPGs)
F flexor motoneurons E extensor motoneurons DC
dorsal columns DRG dorsal root ganglion
Rossignol, 2011
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Evidence of a Motor ProgramCentral 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

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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

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Motor Programming Theories
Writing
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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

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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

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Systems Theory Bernsteins 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

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Systems Theory Bernsteins 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)

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Systems Theory Latashs 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

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Systems Theory Latashs 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

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Postural perturbation study each muscle may be
activated to a different degree by each muscle
synergy
Ting, 2005
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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

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Dynamic Systems Theory Principle of
Self-Organization

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

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Limitation of Systems Theory

• Nervous system is fairly unimportant
• How do we apply mathematics and body mechanics to
  clinical practice?

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Clinical Implications of Systems Theory

• Body is a mechanical system. Consider
  musculoskeletal factors underlying a patients
  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

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Ecological Theory Gibsons 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

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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.
(100-240, 510-730) http//vsx.onstreammedia.co
m/vsx/pbssaf/search/PBSPlayer?assetId68932ccstar
t235620pt0previewundefinedentireyes
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Discuss at your table group

• What are the assumptions of movement control
  underling each of these treatment approaches?

http//www.youtube.com/watch?vr5o5S-9zGpE
http//www.youtube.com/watch?vmCiBehv_FOwfeature
related
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Neurologic rehabilitation approaches
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(No Transcript)
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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 1930s

Kendall Historical Collection
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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

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Reflex- and Hierarchical Based Neurofacilitation
Approaches

• Brunnstrom, Rood, Proprioceptive neuromuscular
  facilitation (PNF), Bobaths 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

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Task-Oriented Approach (motor control of motor
learning approach)
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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?vNhLsh1SW4Ak

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• Moving forward
• .currently available evidence of doseresponse
  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 ConceptKollen, 2009