Cortical motor structures

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 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

Hierarchical Organization of Motor System 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

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

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

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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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11-27 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

Motor cortex