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)

• 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

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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)