Cortical motor structures. Hierarchical Organization of Motor System.
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Transcript of Cortical motor structures. Hierarchical Organization of Motor System.
Cortical motor structures
Hierarchical Organization of Motor System
Hierarchical Organization of Motor System
Primary Motor Cortex and Premotor Areas
Hierarchical Organization of Motor System
Premotor area composed of supplementary motor area and lateral Premotor area
Hierarchical Organization of Motor System
Level 3: The CortexPrimary Motor CortexProjects directly
to the spinal cord to regulate movementVia the Corticospinal Tract
Projects indirectlyVia the Brain stem to regulate movement
Hierarchical Organization of Motor System
Level 3: The CortexPremotor AreasReceive information from parietal and prefrontal areasProject to primary motor cortex and spinal cordFor planning and coordination of complex planned movements
PREMOTOR AREAS (6&8)
M1, PRIMARY MOTOR CORTEX
TRANSCORTICAL CIRCUITS
M1 : somatotopically organized input directly fromBrodmann’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?MusclesMovementDirectionLocationSequence
– Georgopoulous found directional sensitivity in motor cortex neurons.
– Population coding.
Population Vector (vector sum of everycell in the population)
Each arrow shows preferred direction ofcell 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
Comparison of motor planning and execution
• 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.
Comparison of motor planning and execution
• 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.
The motor hierarchy
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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