The Motor Cortex

April 24th 2008

Bijan Pesaran

Nature Reviews Neuroscience 5, 532-546 (2004)

Multiple motor systemsPostural 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

Nature Reviews Neuroscience 5, 532-546 (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)

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

Multiple reference frames

• Direct visuomotor transformation– Supports Area 5 data (Buneo et al 2002)

Direct Transformation

Serial TransformationHead-on-body

positionEye-in-head

position

Eye-centered

target location

Head-centered

target location

Body-centered

target location

Hand-centered

target location

Body-centeredhand position

+-

Motor output

Eye-centered

target location

Hand-centered

target location

Eye-centeredhand 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 thebuttons are lit in order

Now examine same responses whenthe 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 Sclerosis250,000-350,000 total (2002)

• ALS (Lou Gehrig’s Disease) 30,000 total (1999)

Locked in PatientsConstellation 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)