Hierarchical
Organization of
Motor System

Hierarchical Organization of Motor System
Primary Motor Cortex and Premotor Areas

Premotor area composed of supplementary motor area and lateral Premotor area

Level 3: The Cortex
Primary Motor Cortex
Projects directly to the spinal cord to regulate movement
Via the Corticospinal Tract
Projects indirectly
Via the Brain stem to regulate movement

Level 3: The Cortex
Premotor Areas
Receive information from parietal and prefrontal areas
Project to primary motor cortex and spinal cord
For planning and coordination of complex planned movements

M1, PRIMARY
MOTOR CORTEX
PREMOTOR AREAS
(6&8)

TRANSCORTICAL CIRCUITS
M1 : somatotopically organized input directly from
Brodmann’s 1,2,3
(primary somatosensory)
Posterior parietal area 5
(multiple sensory integration for motor planning)

TRANSCORTICAL CIRCUITS
PREMOTOR AREAS: each its own pattern of inputs from distinct locations in areas 5, 7. Area 46 mainly to ventral premotor area
Posterior areas 5&7
Area 46 (prefrontal)-WM for object location in movement guidance

 dense connections between premotor areas (as parts of working memory for motor planning with specific, interconnected aspects)
 lesions result in inability to incorporate visuospatial info in kinematic plan

More on premotor areas function:
(Bereitschaft): 1 sec before movement onset, negative shift in supplementary motor regions
(instructed delayed task, touch 3 panels on visual/memory cues, SMA firing in memory condition)
Self-initiated (e.g from memory) sequence learning
(presupplementary motor area, main input to SMA only, no somatotopy)
Proficiency: shift from SMA to M1 ( e.g. monkeys, learning, lesion, relearning)

LATERAL PREMOTOR: ACTION SELECTION &
SENSORIMOTOR TRANSFORMATIONS
Set-related activity in lateral premotor, usage of sensory stimuli in motion guidance
Persistent during intervals between anticipatory cue and signal to move (dorsal lateral premotor)
Connected to stimuli not conveying spatial cues
Bilateral lesions, intact execution, NO new associative learning (e.g. pull/push joystick on red/blue light)

Motor cortex
What is represented?
Muscles
Movement
Direction
Location
Sequence

– Georgopoulous found directional sensitivity in motor cortex neurons.
– Population coding.
Population Vector
(vector sum of every cell in the population)
Each arrow shows preferred direction of cell associated with arrow. Length of arrow represents strength of preference

Motor cortex

Motor cortex

Motor cortex

Motor cortex

Motor cortex

Motor cortex

Motor cortex

Motor cortex

Motor cortex

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Motor cortex

• Taken together these results are in accord with a hierarchical control system.
– Simple movements
• Minimal processing
• Changes in blood flow limited to primary motor and sensory areas.

• Taken together these results are in accord with a hierarchical control system.
– Greater complexity
• Cortical areas anterior to the primary motor area become activated.
• Activation in both hemispheres
– Activation of abstract motor plan not tied to a specific effector.
– Potential motor plans each viable candidate for achieving a common goal.

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Adapted from Mushiake, H., Masahiko, I., and Tanji, J., Neuronal activity in the primate premotor, supplementary, and precentral motor cortex during visually guided and internally determined sequential movements, Journal of Neurophysiology 66 (1991): 705–718

W. W. Norton

W. W. Norton

W. W. Norton

W. W. Norton

W. W. Norton

W. W. Norton

Motor cortex