● Motor control is hierarchical (p. 327–331 & 336–339)
● Functional neuroanatomy of cortical motor regions (p. 331–335)
● Neural coding in motor regions (p. 339–342, p. 356–357, not p. 343–344)
● Goal selection and action planning (p. 345–349)
● Links between action and perception: Mirror neurons (p. 350–352)
● Movement initiation and the basal ganglia (p. 359–363) • Motor learning: Forward
models and expertise (p. 369–375)
Motor hierarchy
Top: Cortical association,
premotor, and
supplementary motor areas
translating intentions and
goals into action plans and
movement patterns
Middle: Primary motor
cortex, brainstem
structures, basal ganglia
and cerebellum converting
movement patterns into
commands to the muscles
Bottom: Spinal motor
neurons innervating
muscles, together with
spinal sensory neurons
capable of producing simple
reflexes
1. Motor control is hierarchical
Bottom:
Muscle innervation
● Muscles consist of fibers attached to the skeleton
● Come in antagonist pairs: flexor and extensor (if one is flexed/contracted, the other is
extended/relaxed)
● Muscle contraction through acetylcholine released by firing of alpha motor neurons
● Firing frequency of alpha motor neurons (and number of muscle fibers) determines
force generated by muscle
, ● Alpha motor neurons originate in spinal cord, exit through ventral root
● Gamma motor neurons adjust muscle spindles (important for sensing the stretch of
the muscle)
● Sensory neurons entering the spinal cord through dorsal root send input from muscle
spindles to alpha motor neurons via spinal interneurons
Spinal reflexes
● Alpha motor neurons originate in
spinal cord, exit through ventral
root
● Gamma motor neurons adjust
muscle spindles (important for
sensing the stretch of the muscle)
● Sensory neurons entering the
spinal cord through dorsal root
send input from muscle spindles to
alpha motor neurons via spinal
interneurons
● If stretch is unexpected, alpha
neuron activation: stretch reflex
● Reflexes serve postural stability
and protective functions without
any help from the cortex
● Flexor/extensor coordination in
stretch reflex via inhibitory interneuron
Central pattern generators
● Cat walking on a treadmill involving swing (flexion) and stance (extension) even with
transected spinal cord (no connection to the brain)
● Spinal cord alone (without the brain) is capable of producing rhythmic movements
such as walking
● Indicates that the brain does not need to specify patterns of muscle activity but can
simply activate spinal pattern generators
● Cats can walk without a connection from the spinal cord to the brain, humans cannot
Middle:
Brainstem structures
● 12 cranial nerves for critical reflexes involved in breathing, eating, eye movements,
facial expressions originate in brainstem
● Key structures: vestibular nuclei, reticular formation nuclei, substantia nigra
● Projections to spinal cord called extrapyramidal tracts (not part of the pyramidal tract
from motor cortex)
● Extrapyramidal tracts control posture, muscle tone, and movement speed
Cerebellum and basal ganglia
cerebellum
- contains 75% of all neurons of the human central nervous system
- key role in error correction (forward models)
, - damage results in ataxia: difficulty maintaining balance and coordinated movements
basal ganglia
- 5 nuclei with outputs to cortex via thalamus
- key role in movement selection and initiation
(gating function)
- Damage can result in parkinson’s or
huntington’s disease
2. Functional neuroanatomy of cortical motor
regions
Cortical motor regions
primary motor cortex
- key area for motor initiation, activation of lower
levels
- main output: pyramidal (corticospinal) tract
secondary motor areas
- key areas for movement planning and control
- premotor cortex (lateral part of BA6)
- supplementary motor area (medial part of BA6)
Additional key cortical regions
- broca’s area (BA 44/45)
- Inferior (BA 39/40) and superior parietal lobule
(BA 5/7)
- Medial prefrontal cortex inclusief frontal eye
field (BA8)
Primary motor cortex (M1)
Key area for motor initiation (boek bekijken)
- control of movement on opposite side of the
body via corticospinal tract (similar for most
other tracts)
- Hemiplegia after M1 lesion (stroke) loss of voluntary movements on contralateral side
of the body
Corticospinal (pyramidal tract)
- either to spinal interneurons
- or directly with the longest axon in the body (>1m) mono synaptically to alpha motor
neurons (corticomotor neurons) to
control fingers and hands (tool ue)
Somatotopic organization
- different M1 regions represent
different body parts
, - but organization is coarser than in somatosensory cortex (S1) i.e not such clear
homunculus
- representations of effectors correspond to their importance for movement and level of
control
- overrepresentation of hands and lips
- can be mapped with TMS and fMRI
- representation of fingers correspond to how often they are used together
Secondary motor areas
- coarse somatotopic organization similar to M1
- key for planning and control movement
premotor cortex (PM, lateral part BA6)
- connections with parietal cortex: information about body and how it is positioned in
space
- important for sensory-guided movement sequences (e.g. grabbing a cup, hitting a
ball)
supplementary motor area (SMA, medial BA6)
- connections with medial frontal cortex: information about preferences and goals
- important for deciding which object to choose ( coffee or soda) and for
memory-guided movement sequences (playing the piano)
Two dorsal streams to premotor cortex (PM)
Dorsal-dorsal stream to dorsal PM
- from superior parietal lobule: reaching
- Optic ataxia when lesioned: inability to
reach for objects despite intact recognition
Ventro-dorsal stream to ventral PM
- from inferior parietal lobule: transitive
(manipulation of objects) and intransitive
(signify an intention) gestures
- apraxia when lesioned: inability to
coherently use objects (e.g. use a comb)
and to link gestures into meaningful
actions (wave goodbye) despite intact
object knowledge
3. neural coding in motor regions
Coding of movement direction in M1
What do middle/top levels of the hierarchy code
- concrete muscle activity (force) or abstract properties (movement direction or final
location)
- central-out task: move lever to a specific target location (aap)
activity of M1 neurons code movement direction
- Example neuron firing for downwards movement independent of starting and target
location
- many M1 neurons show such directional tuning (‘preferred direction’) → tuning
profiles
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