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 control
Cortico-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 hierarchy
Performing actions is
complicated…
Incorporate:
Visual information
Auditory information
Somatosensory 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
Areas F5 and AIP/PF
Canonical neurons – object specific actions
Regardless of where objects are located
Murata (1997, 2000)
Microstimulations
Story 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 specialization
Damage 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
Cell body
Axon
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
T1
T2
Anatomy – Cortical thickness
Anatomy – Cortical folding
Anatomy – white matter
Tractography
Fiber volume
Fiber length
Brain function
Neurovascular
coupling
Vasculature
Changes in oxygenated blood
‫זמן‬
Heeger et. al. 2002
fMRI experiment
Experimental results
In fMRI we always compare measures over time