The Motor Cortex April 24 th 2008 Bijan
The Motor Cortex April 24 th 2008 Bijan Pesaran
Multiple motor systems Postural Nature Reviews Neuroscience 5, 532 -546 (2004) Voluntary
Postural system is reflexive • Vestibulo-cervical reflex – Stabilize head on body • Vestibulo-spinal reflex – Stabilize limbs on body • Cervico-cervical reflex – Stretch reflex also exists for trunk and limbs • Cervico-spinal reflex – Adjust limb extension based on head angle
Postural reflexes interact
Penfield’s Mapping Experiments
Motor cortex neurons show convergence and divergence
Movements have multiple representations Nature Reviews Neuroscience 5, 532 -546 (2004)
Issues in motor cortical function • Dynamics or kinematics? • Intrinsic or extrinsic? • Force or position control?
Activity follows instruction Tanji & Evarts, JNP 1976
Activity depends on type of movement Tanji & Evarts, JNP 1976
Activity is sustained during a delay
M 1 reflects forces
Population code
Muscles and movements (Kakei et al 1999) • Dissociate coordinate frames – Extrinsic: Direction of movement in space – Joint: Angle of wrist joint – Muscle: Activity of individual or groups of muscles
Kakei et al (1999)
Kakei et al (1999)
• Muscle-like cell responses – Modulated by wrist • Extrinsic cell responses – Modulated by wrist or not • Muscle activity follows muscle-like cell responses – Modulated by wrist Kakei et al (1999)
Multiple reference frames Direct Transformation Eye-centered hand location Eyecentered target location + - Nonlinear 3 D geometry and muscle dynamics Handcentered target location Motor output Serial Transformation Head-on-body position Eye-in-head position Eyecentered target location Headcentered target location Body-centered hand position Bodycentered target location + - Handcentered target location Nonlinear 3 D geometry and muscle dynamics • Direct visuomotor transformation – Supports Area 5 data (Buneo et al 2002) Motor output
Encoding relative position T T-H H Nonlinear 3 D geometry muscle and muscle dynamics T-E H-E E E-H Batista et al 1999 MIP PMd v PM Graziano et al 1997 • Coordinating the hand the eye • Eye-centered • Hand-centered • Relative handeye position • Vectors in abstract space
M 1, Premotor Cortex and Supplementary Motor Area The Monkey knows which to press because the buttons are lit in order
Now examine same responses when the monkey does it from memory
Paralysis: 2. 28 million in U. S. • Stroke 75, 000 per year (2000) • Cervical spine injuries 203, 000 -255, 000 total (2002) • Multiple Sclerosis 250, 000 -350, 000 total (2002) • ALS (Lou Gehrig’s Disease) 30, 000 total (1999)
Locked in Patients Constellation of: • quadriplegia • lower cranial nerve paralysis • mutism • preserved consciousness and cortical function Midbrain or pons injury due to: • stroke • trauma • tumors
Taylor, Helms-Tillery and Schwartz Science (2002)
Taylor, Helms-Tillery and Schwartz Science (2002)
Taylor, Helms-Tillery and Schwartz Science (2002)
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