Theories of Motor Control

THEORIES OF MOTOR CONTROL
Dr. Shweta Kotwani; Pediatric Physical Therapist
BPTh (MUHS); MPT (Neuro,MUHS); LASHS-U.K.
Fellowship Dip.(Peds.Rehab.; Clinical Neuro.Sc.)

OBJECTIVES
• Reflex theory
• Hierarchical theory
• Ecological theory
• Motor Programming Theories
• Systems Theory

REFLEX THEORY
• According to Sir Charles Sherrington, a
neurophysiologist, reflexes were the building
blocks of complex behaviour
• Complex behaviour = combined action of
individual reflexes that were chained together

REFLEX THEORY
• Limitations-
1. Reflex cannot be considered the basic unit of
behaviour
2. Reflex theory of motor control does not predict
movement in the absence of sensory stimulus
3. The theory does not explain fast movements
4. A single stimulus can result in varying responses
5. Reflex chaining does not explain the ability to
produce novel movements

REFLEX THEORY
• Clinical Implications-
1. Reflex theory of motor control can be used to
interpret a patient’s behaviour.
2. A patient’s movement behaviours would be
interpreted in terms of the presence or absence
of controlling reflexes
3. Retraining motor control for functional skills
would focus on enhancing or reducing the effect
of various reflexes during motor tasks.

HIERARCHICAL THEORY
• The brain has higher, middle, and lower levels
of control, equated with higher association
areas, motor cortex, and spinal levels of motor
function
• Organizational control that is top down i.e.
each successively higher level exerts control
over the level below it.

HIERARCHICAL THEORY
TOP
DOWN
The hierarchical control
model is characterized
by a top-down structure,
in which higher centres
are always in charge of
lower ones.

HIERARCHICAL THEORY
• Rudolf Magnus, found that reflexes controlled
by lower levels of the neural hierarchy are
present only when cortical centres are
damaged.
• Reflexes are part of a hierarchy of motor
control, in which higher centres normally
inhibit these lower reflex centres

HIERARCHICAL THEORY
• The development of human mobility in terms
of the appearance and disappearance of a
progression of hierarchically organized
reflexes. (Georg, 1928)
• Pathology of the brain may result in the
persistence of primitive lower level reflexes

HIERARCHICAL THEORY
• Stephan Weisz (1938) described the ontogeny
of equilibrium reflexes in the normally
developing child and proposed a relationship
between the maturation of these reflexes and
child’s capacity to sit, stand and walk.
• Thus this theory suggests that motor control
emerges from reflexes that are nested within
hierarchically organized levels of the CNS.

HIERARCHICAL THEORY
The Neuro-maturational theory of motor control attributes motor
development to the maturation of neural processes, including the progressive
appearance and disappearance of reflexes

HIERARCHICAL THEORY
• Limitations-
1. It cannot explain the dominance of reflex
behaviour in certain situations in normal
adults. Eg. Stepping on a pin results in
immediate withdrawal of the leg. It is an
example of bottom-up control.
2. Low level behaviours = primitive, immature
and non-adaptive
Higher level (cortical) behaviours = mature,
adaptive and appropriate.

HIERARCHICAL THEORY
1. Brunnstrom, used this theory to describe
disordered movement following a motor
cortex lesion. When the influence of higher
centres is temporarily or permanently
interfered with, normal reflexes become
exaggerated and pathological reflexes
appear.

HIERARCHICAL THEORY
2. Bobath, she stated that the release of motor
responses in children with CP integrated at
lower levels from restraining influences of
higher centres, especially that of the cortex
leads to abnormal postural reflex activity.

ECOLOGICAL THEORY
• Actions require perceptual information that is
specific to a desired goal-directed action
performed within a specific environment.
• The organization of action is specific to the
task and environment in which the task is
being performed.
• Perception focuses on detecting information
in the environment that will support the
actions necessary to achieve the goal.

ECOLOGICAL THEORY
• This theory states about the understanding of
nervous system function from that of a
sensory/motor system, reacting to
environmental variables, to that of a
perception/action system that actively
explores the environment to satisfy its own
goals.

ECOLOGICAL THEORY
• Limitations-
• Less emphasis to the organization and
function of the nervous system than the
interaction of the organism and the
environment.

ECOLOGICAL THEORY
1. The active exploration of the task and the
environment in which the task is performed
allows the individual to develop multiple
ways to accomplish a task.
2. Adaptability is important not only in the way
one organizes the movements to accomplish
a task, but also in the way to use perception.

ECOLOGICAL THEORY
• The ability to develop multiple adaptive
solutions to accomplish a task requires that
the patient explore a range of possible ways to
accomplish a task and discover the best
solution, given his or her set of limitations.

MOTOR PROGRAMMING THEORIES
• A motor program theory of motor control has
considerable experimental support- studied
motor control in the grasshopper and showed
that the timing of the animal’s wing beat in flight
depended on the rhythmic pattern generator.
• Even when the sensory nerves were cut, the
nervous system by itself could generate the
output with no sensory input; however the wing
beat was slowed (Wilson, 1961)

• This theory suggested that movement is
possible in the absence of reflexive action.
• Sensory input, while not essential in driving
movement, has an important function in
modulating action.
• The term motor program is used to identify a
central pattern generator (CPG) that is a
specific neural circuit like that for generating
walking in the cat. (Grillner 1981)

• In the cat, spinal neural networks could produce a
locomotor rhythm with neither sensory inputs
nor descending patterns from the brain.
• By changing the intensity of stimulation to the
spinal cord, the animal could be made to walk,
trot or gallop.
• Thus it showed that reflexes do not drive action,
but that CPG (spinally mediated motor programs)
by themselves can generate such complex
movements.

• The term motor program is also used to
describe the higher level motor programs that
represent actions in more abstract terms.
• This concept of central pattern generators
expanded the understanding of the role of the
CNS in the control of movement.
• This theory explained the ability of the
nervous system in creating movements in
isolation from feedback.

• A significant amount of research in the field of
psychology has supported the existence of
hierarchically organized motor programs that
store the rules for generating movements so
that one can perform tasks with a variety of
effector systems (Keele, 1968)
• Lab Activity.

Abstract
motor
program
Synergy
Right hand
muscles
Synergy
Left hand
muscles
Synergy
Right arm
muscles
Levels of control for motor programs and their output systems. Rules for action are
represented at the highest level, in abstract motor program. Lower levels of the
hierarchy contain specific information, including muscle response synergies,
essential for effecting action.

• Limitations-
• CMP cannot be considered to be the sole
determinant of action (Bernstein, 1967)
Eg. 2 identical commands to the elbow flexors will
produce different movements depending on
whether the arm is resting at side or the patient
is holding the arm in front.
Thus, the forces of gravity will act differently on the
limb in the two conditions and thus modify the
movement

• Limitations-
• If the patient’s muscles are fatigued, similar
nervous system commands will yield different
results.
• Thus, motor program concept does not take
into account that the nervous system must
deal with both MSK and ENVT variables in
achieving movement control.

• This theory explains about abnormal movements- resulting
from abnormalities in CPG or in higher level motor programs.
• In patients, whose higher levels of motor programming are
affected, motor program theory suggests the importance of
helping patients relearn the correct rules for action.
• Intervention should focus on retraining movements important
to a functional task, not just on re-educating specific muscles
in isolation.

SYSTEMS THEORY
• Nicolai Bernstein, looked at the whole body as a
mechanical system, with mass and subject to
both external forces such as gravity and internal
forces such as both inertial and movement-
dependent forces.
• Bernstein also suggested that control of
integrated movement was probably distributed
throughout many interacting systems working co-
operatively to achieve movement.
• This gave rise to the concept of a distributed
model of motor control (Bernstein, 1967)

SYSTEMS THEORY
• Body as a mechanical system- many degrees of
freedom.
• Eg. Depending on the degree of freedom- joint
which can flex or extend can be rotated as well.
• Bernstein said, ”Co-ordination of movement is
the process of mastering the redundant degrees
of freedom of the moving organism”
• Converting the body into a controllable system.

SYSTEMS THEORY
• Degrees of freedom- hierarchical control exists to
simplify the control of the body’s multiple
degrees of freedom.
• Higher levels activate lower levels
• Lower levels activate synergies or group of
muscles that are constrained to act together as a
unit
• Eg. When demands of a task increase, control
signal to the synergy increases, leading to parallel
increases in the activation in all muscles in the
synergy

SYSTEMS THEORY
• Synergies ensure flexible and stable performance
of motor tasks-principle of abundance
• Synergy is a neural organization of a multi
element system (eg. Muscles) that: (a) organizes
sharing of a task among a set of elemental
variables (eg. muscles) and (b) ensures
covariation among elemental variables with the
purpose of stabilizing performance variables (eg.
COM in posture control or the end point in a
reaching task)

SYSTEMS THEORY
• Synergies, a muscle belongs to only one
synergy and muscles within a synergy are
activated equally as a unit.
• Thus, the total activation of a muscle is
dependent on both simultaneous activation of
multiple synergies containing that muscle and
the relative contribution of that muscle within
each of these synergies.

SYSTEMS THEORY
• ”Self-organization”, is a fundamental principle of
dynamic systems theory; states that when a
system of individual parts comes together, its
elements behave collectively in an ordered way.
• There is no need for “higher” center issuing
instructions or commands in order to achieve
coordinated action. This principle applied to
motor control predicts that movement could
emerge as a result of interacting elements,
without the need for specific commands or motor
programs within the nervous system.

SYSTEMS THEORY
• Limitations-
• Dynamic systems theory takes into account not only
the contributions of the nervous system to action but
also the contributions of the muscle and skeletal
systems, as well as the forces of gravity and inertia, it
predicts actual behavior much better than the previous
theories.
• This theory reminds that the nervous system in
isolation will not allow the prediction of movement.
• Principles of body mechanics play a more dominant
role in describing motor control than the nervous
system alone.

SYSTEMS THEORY
• Clinical Implications
1. Importance of understanding the body as a mechanical
system. Movement is determined by the output of the
nervous system as filtered through a mechanical system,
the body. When working with a patient with CNS deficit,
the therapist must be careful to examine the contribution
of impairments in the MSK system as well as the neural
system to the overall loss of the motor control.
 Systems theory suggests that examination and intervention
must focus not only on the impairments but also on the
effect of interacting impairments among multiple systems
contributing to motor control.

SYSTEMS THEORY
• Clinical Implications
2. Variability- characteristic feature of normal movement.
When variability is viewed as a consequence of error-
therapists will use the therapeutic strategies designed to
reduce error, guiding patients towards an optimal and
stable movement patterns
When variability is viewed as a critical element of
normal function- therapists will encourage patients to
explore variable and flexible movement patterns that will
leas to success in achieving performance goals.
(Harbourne & Stergiou, 2009)

NEUROLOGIC REHABILITATION
MODELS
PARALLEL DEVELOPMENT OF THEORIES OF MOTOR CONTROL AND
CLINICAL PRACTICES
REFLEX
MUSCLE
REEDUCATION
HIERARCHICAL
NEUROTHERAPEUTIC
FACILITATION
SYSTEMS
CONTEMPORARY
TASK-ORIENTED
Neurofacilitation approaches include Bobath, Rood, Brunnstrom, PNF, SI
are based largely on assumptions drawn from both reflex and hierarchical
theories of motor control.

REFERENCES
• MOTOR CONTROL, Translating Research into
Clinical Practice; Fourth Edition; Anne
Shumway-Cook, Marjorie H. Woollacott.

Theories of Motor Control

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Theories of Motor Control