Cortical, Cerebral And Vestibular Control Of Movement

Front 1

Feedback control of
motor behaviors

Back 1

1. Utilize afferent information on moment to
moment basis

2. sensory signal compared with desired state (i.e., internal representation) –reference signal

3.Difference between actual and intended behavior –error signal

4. Negative/proportional feedback in closed loop
chain (e.g., thermostat)

5.Gain of feedback (ratio of input to output)

Front 2

Feedforward control of
motor behaviors

Back 2

Motor commands in advance to
“expected” perturbations
 Open loop control
 Feedback signals do not
contribute to second to
second variations in behavior
 Generation of an internal
model of desired state
 Still dependent on sensory
information, but a
“representation” of this
information
 raising a weight while
standing
 catching a ball

Front 3

General Concepts Regarding Control of
Volitional Tasks

Back 3

Motor actions have similar features regardless of conditions
(Donald Hebb 1950s)
 trajectory of reaching
 handwriting examples

Front 4

General Concepts Regarding Control of
Volitional Tasks

Back 4

Motor actions have similar features regardless of conditions
(Donald Hebb 1950s)
 trajectory of reaching
 handwriting examples
 Motor plan
 movement is planned by higher centers
 abstract form; not series of contractions/consequences
 Motor program - signal to specify
the intended movement given the
biomechanical constraints

Front 5

Neural Basis of
Voluntary Movement

Back 5

Sensorimotor cortex – skilled
movements

Basal Ganglia – initiation and
selection of motor programs

Cerebellum – coordination, timing,
learning

Front 6

Sensorimotor cortex – skilled
movements

Back 6

 Frontal lobe
– Primary motor cortex (M1,Area 4)
– Premotor cortex (PM, Area 6)
– Supplementary motor area (SMA,
Area 6)
 Parietal lobe
– Primary sensory cortex (S1, Area
1,2,3)
– Posterior partial cortex (Areas 5,
7)

Front 7

Primary motor cortex

Back 7

participates in specific
trajectory planning

delivers commands to lower
levels for initiation/
modulation of movement

Motor programs located here
or at lower levels (CPGs,
interneuron networks)

Front 8

Primary somatosensory
cortex

Back 8

provides sensory information
required for movement
planning and initiation

modulation of ongoing
movement

Front 9

Primary cells

Back 9

Layer 5 – pyramidal
cells (include large Betz cells),
distributed in specific cortical
areas

Front 10

Cortical maps

Back 10

(Penfield 1930-50s)
stimulated the primary
somatosensory cortex - asked the
patient about the sensation

Front 11

Obtained movements with
stimulation in primary motor
cortex

Back 11

The results led to a debate
about whether muscles or
movements were represented in
the cortex.

individual muscles are
represented in many locations.

Front 12

Cortical control of movement

Back 12

Specific cortical areas participate of specific movements/body parts -
homunculus (“little man”)

The area of cortex dedicated to processing information from a
particular body part reflects the degree of innervation of that body
part.

PM and SMA demonstrate similar topography

Front 13

corticospinal tract (CST)

Back 13

comprises
~ 1 million descending axons.
 At the junction of the medulla and
spinal cord, the CST divides into ventral
and lateral tracts.
 Ventral CST projects bilaterally to
motor neurons that innervate axial
muscles and to the intermediate
zone.
 Lateral CST (shown here) projects to
motor neurons of distal muscles and
interneurons in intermediate zone.
 Some axons make monosynaptic
connections onto motor neurons,
particularly those that control finger
movements.
 Other fibers synapse on interneurons
within the spinal cord.

Front 14

activate cortical
neurons indirectly/non-invasively

Back 14

Transcranial magnetic stimulation
(TMS) – also Transcranial
Electrical Stimulation (TES)
 Magnetic coil generates field
along cortical surface
 Faraday’s law – electrical
current generated in “wires”
(axons)
 Activate smaller cortical
cells which activate
pyramidal cells
(TES may bypass this, though
mechanisms controversial)

Front 15

Multiple pathways

Back 15

Multiple pathways to spinal
cord/brainstem encode
similar information
 Cortical tracts
 40% from M1 region
 S1 and PM areas contribute
significantly
 Typically to interneuron
pools – except to distal
motor pools

Front 16

executing movements

Back 16

 Corticospinal neurons make
direct excitatory connections
with only some motor neurons
 Direct connections for fine control
of the digits.
 After a bilateral resection of the
corticospinal tracts, monkeys unable
to grasp small objects with
thumb/index finger

Front 17

Walking after bilateral resection

Back 17

Walking after bilateral resection,
– unable to negotiate in feedforward
manner (obstacles, balance beam/ladder)
– Toe/ankle dorsiflexion problems, can’t
walk balance beam

Front 18

discharge of action potentials

Back 18

The discharge of action potentials by neurons in the primary motor
cortex (CM = corticomotoneuronal cell) depends on the motor task.
 Precision vs Power grip involve separate cortical/subcortical
circuits acting on similar IN/MN pools

Front 19

Direction-specific encoding of cortical
cells

Back 19

Population vectors encode both direction
and magnitude

Front 20

Motor cortical cells also encode for force

Back 20

Motor cortical cells alter firing
patterns according to extent of
muscle activity required to complete a
task
 Tonic and Phasic cortical cells may
participate

Front 21

Premotor area

Back 21

involved in goal-directed movements

Activity prior to visually-guided movements

Front 22

Supplementary motor area

Back 22

ensures correct sequencing of movement (order of
movement)
– biomechanical constraints
– task performed
– external conditions
 Activity prior to internally-guided movements

Front 23

Posterior parietal cortex

Back 23

encodes complex sensory information

internal sensory representation

Front 24

Four “premotor” areas

Back 24

 Lateral premotor areas
– Dorsal premotor
– Ventral premotor
 Medial premotor areas
– Supplementary motor area
– Cingulate area

Front 25

Differences in neural substrates of
movement dependent on task

Back 25

Alteration in Premotor (dorsal or ventral) and

Supplementary motor area during visually guided vs.
internally guided movements
 Similar in humans and non-human primates

Front 26

Supplementary Motor Areas

Back 26

-activated during sequential versus simple movements

-active during mental rehearsal

Front 27

Ventral and Dorsal Premotor Areas

Back 27

Different tasks utilize different pathways with external ques

- reaching-visual parietal dosal and PM areas
- grasping- visual parietal ventral and PM areas

Front 28

Generic pathway for initiation of
volitional movements

Back 28

Visual/Auditory association cortices and
Internal representation of body
and space (Posterior Parietal
Cortex)

Dorsolateral Prefrontal Cortex (DLPFC)

Premotor or Supplementary Motor Areas

Primary Motor Cortex

Front 29

three
levels of control

Back 29

spinal cord, brain stem, cerebral cortex

Front 30

basal ganglia & cerebellum

Back 30

1. Two systems of brain stem
neurons (medial and lateral
descending systems) receive input
from the cortex & subcortical
nuclei and project to the spinal
cord

2. The cerebellum and basal ganglia
provide feedback through the
thalamus (not shown) that regulate
cortical and brain stem motor
areas.

Front 31

basal ganglia

Back 31

involved in
motivation and initiation and
selection of motor programs.

Front 32

cerebellum

Back 32

is involved with
the timing and coordination of
movements (error detection) and
with the learning of motor skills.

Front 33

Equilibrium

Back 33

Vestibular apparatus
(inner ear, CN VIII)
-Semicircular canals –
directional rotational
accel/deceleration
-Utricle and saccule

Front 34

Utricle and saccule

Back 34

 Changes in rate of
linear movement

 Determining head
position in relation to
gravity

Front 35

kinocilium and stereocilia

Back 35

Neural signals generated in response to
mechanical deformation of hair cells
– Semicircular canals – cupula
– Utricle/saccule

Movement triggered by fluid
movement or particle movement
– Endolymph
– Otolith (Ca crystals embedded)

Front 36

vestibular nuclei in brain
stem

Back 36

Superior/medial from
semicircular and otolilths –
output to Medial
Longitudinal Fasciculs
(MLF)

Lateral (Dieter’s nucleus)
projects to lateral
vestibulospinal tract

Descending nucleus inputs
from otolisths – projects to
cerebellum/RF and SC

Front 37

Extraocular muscles

Back 37

Four are rectus muscles (straight)

Two are oblique: superior and inferior

Front 38

Cranial nerve innervations:

Back 38

Lateral rectus: VI (Abducens n.) – abducts eye outward

Medial, superior, inferior rectus & inf oblique: III (Oculomotor n.) –
able to look up and in if all work

Superior oblique: IV (Trochlear n.) – moves eye down and out

Front 39

MLF

Back 39

medial longitudinal
fasciculus

Front 40

PPRF

Back 40

paramedian pontine
reticular formation
Rostral interstitial nucleus –
anterior midbrain RF (MLF)

Front 41

Vestibulo-ocular reflex

Back 41

– keep the eyes still in space when the head
moves

Front 42

Vestibulo-colic reflex

Back 42

keeps the head still in space – or on a level
plane when you walk.

Front 43

Vestibular-spinal reflex

Back 43

adjusts posture for rapid changes in
position.

Front 44

Lateral vestibular nucleus/spinal tract

Back 44

•Descends the ipsilateral spinal
chord

•Terminates at all levels of the spine.

•Excitatory pathway activates
postural muscles (proximal to spine)
to correct for leftward listing

Front 45

Medial vestibular nucleus/spinal tract

Back 45

•Descends ipsilateral and
contralateral spinal cord but
asymmetrically

•Terminates in the cervical and
thoracic spine.

•Excitatory pathway activates
postural muscles (proximal to spine)
mainly in the neck.

Front 46

Ascending projections to oculomotor nuclei

Back 46

•Both direct contralateral and indirect ipsilateral control of extra ocular muscles

•Counters head movements to keep image stable on retina.

•Damage of vestibular nerve/nuclei causes nystagmus a oscillation of horizontal eye movement.

Front 47

Gaze stabilization

Back 47

 Vestibuloocular reflex (VOR) – stabilize eyes relative to external world
by compensating head movements

 Optokinetic nystagmus – elicted by moving object that produce illulsion or head movement (visual ocular response)

Front 48

Gaze shifting

Back 48

Vergence – aligns fovea of each eys with targets and different distances

Smooth pursuit – keep moving stimuli on fovea

Saccades – ballistic movements that abruptly change point of fixation

Front 49

Saccades

Back 49

MLF – allows
coordination of
conjugate eye
movements

PPRF –initiates fast
horizontal saccadic
movment

Rostral interstitial
nucleus – fast vertical
saccadic eye movements

Front 50

Double vision

Back 50

diplopia (divergent eye movement)

Front 51

Misalignment:

Back 51

strabismus (what is observed when shine a
light: not reflected in the same place on both eyes) – can be a cause of diplopia

 Cross eyed
 Gaze & movements not conjugate (together)
 Medial or lateral, fixed or not
 Many causes
– Weakness or paralysis of extrinsic muscle of eye
– Oculomotor nerve problem, other problems

Front 52

Lazy eye

Back 52

amblyopia

Cover/uncover test at 5 yo

If don’t patch good eye by 6, brain ignores lazy eye and visual

pathway degenerates: eye functionally blind

Front 53

cerebellum

Back 53

 Receives information about goals,
commands, and feedback signals
associated with the execution of
movement

 40X more axons project into it than
exit it (Greater number of neurons
than rest of CNS)

 Assists with spatial accuracy and
coordination of movement

 Largely motor function, some
cognitive

 Lateralization, topography of
organization

 Input and output: descending, spinal,
brainstem pathways

Front 54

Vestibulocerebellum

Back 54

Flocculonodular lobe (most primitive)

Receives vestibular, postural, ocular
information; controls balance and eye
movements

Front 55

Spinocerebellum (Vermis)

Back 55

 Intermed hemisphere and Vermis –
interposed and fastigial nuclei

proprioceptive/exteroceptive inputs

Governs “performance of movement”

Front 56

Cerebro- (ponto-) cerebellum
(anterior/posterior lateral areas)

Back 56

 Lateral hemisphere –Dentate nuclei

Projections from pontine nuclei

 Information of planned movement

Front 57

Cerebellum cortical layers

Back 57

Molecular layer
 Stellate and basket cells
 Axons of Granule cells
(parallel fibers)
 Terminals of climbing fibers
 Dendrites of Purkinje cells

Purkinje cell layer
(projection neurons to nuclei)

Granular layer
 Granule cells
 Inputs from mossy fibers

Front 58

Mossy fibers

Back 58

Originate from SC/BS nuclei

Carry sensory and some cortical
information

Mossy to granule (parallel
fibers) to Purkinje (generates
simple spikes)

Front 59

Climbing fibers

Back 59

from inferior olivary nucleus

Receives SC/cortical
information

Climbing to Purkinje
(generate complex spikes –
may depress parallel input)

Front 60

Cerebellar outputs

Back 60

cortical and brainstem

Front 61

Role of Cerebellum

Back 61

Role in Memory
 Place Cells
 Motor Learning?

Role in Error
correction

Front 62

Transitions

Back 62

immediate change in behavior

driven by prior experience and the ability to predict that new demands will exceed “current state” (feed-forward
strategies)

Front 63

Adaptations

Back 63

Gradual change in behavior that results from experience
(“feedback strategies”)

Driven by demands that exceed “current state”

Front 64

Learning

Back 64

Relatively permanent changes

Resulting from repeated exposure (adaptation may be a precursor)

Front 65

Prism adaptation

Back 65

Prisms inserted into eyeglasses
 Displace visual field
 Leads to initial errors in movement accuracy\

With extensive training, throwing with wedge prisms can become a skill.

Adaptations results in Learning – which allow faster
Transitions

Front 66

Locomotor Adaptations

Back 66

“Podokinetic system” - circuits
that allow directional control
of locomotor trajectory
through foot contact with the
floor (Weber et al. 1998.)

Front 67

Walking on a circular treadmill

Back 67

 Angular velocities (11-60º/s);
duration (7.5-60 minutes)

Stepping performed over
rotational axis or on perimeter

instructed to step in-place or walk
in a straight line on a circular
rotating treadmill

Front 68

“Podokinetic” Adaptation (PKA)

Back 68

 Subjects generate curved
walking trajectories with
blindfolds

Walking forward “in a straight
line”

Rotation while walking in place

Subjects unaware of trajectories

Front 69

Termed...

Back 69

podokinetic afterrotation (PKAR)

Recalibration of trunk and limb
position with vestibular
information

Transfers to overground backward
walking

Front 70

How does PKAR occur?

Back 70

Podokinetic stimulation

Overground transfer

General adaptation of
locomotor trajectory control
during stepping vs. specific
remodeling to adaptive
stimulus

Front 71

Podokinetic stimulation

Back 71

 Clockwise rotation, foot
turning relative to trunk

trunk must stabilize by
turning counterclockwise

Front 72

Overground transfer

Back 72

No PK stimulation

Negative aftereffects of
continued CCW rotation of
trunk on stable foot

Front 73

Disruption of cerebellar circuits

Back 73

Ataxia in humans

Surgical cooling of dentate
and interpositus nucleui

Disruption of the error
correction process?