The Motor Cortex April 24 th 2008 Bijan Pesaran

Nature Reviews Neuroscience 5, (2004) Multiple motor systems PosturalVoluntary

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

Nature Reviews Neuroscience 5, (2004) Movements have multiple representations

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

M1 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

Multiple reference frames Direct visuomotor transformation –Supports Area 5 data (Buneo et al 2002) Direct Transformation Serial Transformation Head-on-body position Eye-in-head position Eye- centered target location Head- centered target location Body- centered target location Hand- centered target location Body-centered hand position + - Motor output Eye- centered target location Hand- centered target location Eye-centered hand location + - Nonlinear 3D geometry and muscle dynamics Motor output Nonlinear 3D geometry and muscle dynamics

MIP PMd Nonlinear muscle dynamics Encoding relative position Nonlinear 3D geometry and muscle dynamics Batista et al 1999 Graziano et al 1997 H T E T-E E-H H-E T-H PMv Coordinating the hand and the eye Eye-centered Hand-centered Relative hand- eye position Vectors in abstract space

M1, 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 total (2002) Multiple Sclerosis 250, ,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)