Motor system basics
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Transcript of Motor system basics
Motor system basics
Development
Motor neurons & Muscle fibers
Local motor control
Muscle spindles enforce the “stretch reflex”: feedback about muscle length.
Golgi tendon provide feedback about level of force.
Spinal chord
Central pattern generators
Taking care of the basic simple functions...
Central pattern generators
Central pattern generators
Decerebrate walking cat
Central pattern generators
Decerebrate walking cat
Cortical control
Postural control
Vestibular and Reticular nuclei (medial motor system).
Adaptation and Anticipation – Sailor “sea legs”
Voluntary controlCortico-spinal and Rubro-spinal pathways (lateral motor system).
Fine motor control.~ 1 Million fibers originating in:• Primary motor cortex (one third)• Premotor cortex (one third)• Somatosensory cortex (one third)
Motor system hierarchy
Motor system hierarchyPerforming actions is complicated…
Incorporate:Visual informationAuditory informationSomatosensory information
Make a decision
Make a motor plan (timing, forces, balance, etc…)
Execute
Somatotopic organization of M1
Encoding of M1 neurons: Force
Encoding of M1 neurons: Direction
Textbook stories describe M1 neurons as responsible for the final motor execution step…
Higher motor levels
Visual – movement performed according to cue.
Internal – movement performed as part of a memorized sequence.
Anterior parietal & Premotor cortex
Visuomotor coordination
Object manipulation
Grasping
Canonical neurons – object specific actionsRegardless of where objects are located
Areas F5 and AIP/PF
Murata (1997, 2000)
MicrostimulationsStory is a bit more complex.Long microstimulations in premotor, anterior parietal, and primary motor cortex generate complicated multi-effector movements.
Like grasp to eat…
Idea of motor primitives
Supplementary motor cortex
Neurons that respond to a specific movement only when it is part of a sequence (a) or to any movement, but only according to its location in the sequence (b).
Functional specializationDamage in M1 creates weakness in the relevant part of the body.
Damage in parietal and premotor cortex creates problems with movement planning and coordination.
Damage in SMA creates problems with learning new movement sequences
Motor control
What is the purpose of the motor system?
Encoding space
Head centered?Hand centered?Eye centered?
Inverse model
You need to translate external space to internal space…
Inverse model
Eventhough you use different joints and muscles for different movements:
Movements remain straight, smooth, with symmetric velocity profile.
Your motor system cares about making smooth efficient movements in external space…
(Morasso 1981)
Motor primitives
Invariance to scale…
Motor primitives
Invariance to effector…Raibert 1977
Inverse model is flexible…
(Brashers-Krug, Shadmehr, and Bizzi 1996)
Inverse model is flexible…
Motor memory
Where does motor learning happen?
How do we study neurophysiology?
Dendrites
Axon
Cell body
Neural activity
In vitro electrophysiology
Control > ASD
In vivo electrophysiology
Control > ASD
In vivo electrophysiology
Control > ASD
Anesthetized or awake
Electrode location
Control > ASD
Magnetic resonance imaging (MRI)
Anatomy - Separating tissues
1T 2T
Anatomy – Cortical thickness
Anatomy – Cortical folding
Anatomy – white matter
TractographyFiber volumeFiber length
Brain function
Neurovascular coupling
Vasculature
Changes in oxygenated blood
Heeger et. al. 2002
זמן
fMRI experiment
Experimental results
In fMRI we always compare measures over time