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The Motor Cortex . April 24 th 2008 Bijan Pesaran. Multiple motor systems. Postural. Voluntary. Nature Reviews Neuroscience 5 , 532-546 (2004) . Postural system is reflexive. Vestibulo-cervical reflex Stabilize head on body Vestibulo-spinal reflex Stabilize limbs on body - PowerPoint PPT Presentation
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The Motor Cortex
April 24th 2008Bijan 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
ET-E
E-HH-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 Sclerosis
250,000-350,000 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)
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