Transcript Motor Cortex

Cortical Control
of Movement
Lecture 22
Hierarchical Control of Movement
Association cortices & Basal Ganglia
 strategy : goals & planning
 based on integration of sensory info
 Motor cortex & cerebellum
 tactics: activation of motor programs
 Spinal cord
 execution: activation of alpha motor
neurons ~

Sensorimotor Cortical System
Integration of sensory information
and directed movements
 Anatomy
 Descending spinal tracts
 Lateral pathway

Pyramidal Motor System


Ventromedial pathway
Extrapyramidal pathway ~
Cortical Anatomy
S1 - postcentral gyrus
 PPC - Posterior Parietal Cortex
 M1 - Precentral Gyrus
 Frontal Lobe
somatotopic organization
 M2 - Secondary Motor Cortex
SMA - Supplementary Motor Area
PM - Premotor Cortex

SMA
M1
S1
PM
PPC
Sensorimotor Pathways
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SMA
M1
PM
S1
PPC
Primary Motor Cortex
Somatotopic organization
 neurons have preferred direction
of movement
 Motor homunculus ~

M1: Coding Movement
Movement for limbs
 Neuron most active
 Preferred direction
 but active at 45 from preferred
 How is direction determined?
 Populations of M1 neurons
 Net activity of neurons with
different preferred directions
 vectors ~

M1: Coding Movement
Implications
1. MostM1 active for every
movement
2. Activity of each neuron
1 “vote”
3. direction determined by
averaging all votes ~

Motor Association Cortex

Motor area other than M1
secondary motor cortex (M2)
Premotor & Supplemental Motor Areas
 Stimulation - complex movements
 motor programs
 Active during preparation for movement
 Planning of movements

e.g. finger movements ~
Supplementary Motor Area - SMA
Primarily midline cortex
 Input from PPC and prefrontal
 Bilateral output to M1
 Distal & proximal limbs
 closing hand, orienting body ~

Premotor Area - PM
Anterior to M1
 Input primarily from PPC
 Reciprocal connections with SMA
 Outputs to M1
 Proximal & axial muscles
 orienting body & arm to target ~

Planning Movements

Targeting vs trigger stimulus
recording activity of neurons
active when movement planned
 for specific direction
 Different populations of neurons active
 during planning (targeting)
 & execution (trigger stimulus)
 PM active before movement ~

The Descending Spinal Tracts
Brain to Spinal Cord
Upper motor neurons
 communication with lower (a) motor
neurons
 Lateral pathway
 direct cortical control
 Ventromedial pathway
 brain stem control ~

The Lateral Pathway
Voluntary movement
 distal limbs
 2 tracts
 Corticospinal tract
about 1 million axons
 Cortico-rubrospinal tract
 facial muscles


cranial nerves ~
Spinal Cord: Lateral Pathway
Dorsal
Ventral
Corticospinal
tract
Corticorubrospinal
tract
Corticospinal tract
Also called Pyramidal tract
 Motor cortex ---> spinal cord
 uninterrupted axon
 2/3 of axons from motor cortex
 1/3 from somatosensory cortex
 Decussates at medullary pyramids
 Contralateral control movement ~

The Cortico-rubrospinal Tract
Motor Cortex ---> red nucleus
 Red nucleus ---> spinal cord
 inputs from motor cortex
 bigger role in other mammalian
species ~

Lateral Pathway Damage
Lesion both tracts
 no independent movement of distal
limbs
 voluntary movements slow & less
accurate
 Corticospinal only
 same deficits
 recovery over several months
 compensation by rubrospinal tract ~

The Ventromedial Pathway
Neurons originate in brainstem
 Vestibulospinal & tectospinal tracts
 head & posture posture
 orienting responses
 Pontine & medullary reticulospinal tracts
 originate in reticular formation
 trunk & antigravity leg muscles
 tracts are antagonistic ~

Spinal Cord: Ventromedial Pathway
Dorsal
Vestibulospinal
tract
Tectospinal
tract
Medullary
Reticulospinal
tract
Ventral
Pontine
Reticulospinal
tract
Major Descending Spinal Tracts
Motor Cortex
Lateral
Red
Nucleus
Ventromedial
Reticular
Nuclei
Spinal cord
Superior Colliculus
vestibular nuclei
Sensorimotor Integration
Somatosensory cortex
provides spatial coordinates
 Motor Cortex
executes movements
 Results in meaningful behavior ~
