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MSc CogNeuro
Lecture 1-2: Intro
+ Primary Motor Cortex (MI)
www.psychol.ucl.ac.uk/patrick.haggard/MSC/msc_1.ppt
Action
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Behaviour
Movement
Cognition
Survival
Brain control to action
• Not conscious
• Computational processes
• Learning
Computational process
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Volition
Selection
Initiation
Execution
Monitoring
Stopping
I want to do X
How will I do X?
Start to do X
Movement towards…
Have I got there yet…
Deactivate X
• NOTE: Process is serial, hierarchical, and
information expansion
Computational model of action control
(Blakemore, Wolpert, Frith, Trends in Cognitive Science, 2002)
Goal/
Intention
Planner
(Inverse model)
motor command
Limb
efference copy
Forward model
sensory feedback
Provisional Road Map (PH)
• A backwards hierarchy
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(Muscle)
Primary motor cortex
Premotor cortex (preparation)
Supplementary motor area (physiology, psychology)
Basal Ganglia (physiology, neurology)
Cerebellum (physiology, neurology)
Cortical association circuits (somatosensory, social)
Primary motor cortex (MI)
Layered structure of cortex
•Descending output from layer 5
•(pronounced in cortex)
•Layer 4 absent
•Betz/pyramidal cells
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Fine-grained
local somatotopy
in MI is quite
fractured/overlap
ping
Several MI zones
produce same
movement when
stimulated
Perhaps each
movement is
represented once
for each task or
synergy? We
don’t know…
Rathelot & Strick
(2006). Muscle
representation in the
macaque motor cortex:
An anatomical
perspective. PNAS,
103, 8257-8263
Rathelot &
Strick (2006).
Muscle
representati
on in the
macaque
motor
cortex: An
anatomical
perspective.
PNAS, 103,
8257-8263
Lateral corticospinal tract (Pyramidal tract)
Fine motor control of contralateral muscles
Kuypers (1968)
Corticomotoneuronal cell: 1 synapse from muscle
- Cell body in MI, leaves via pyramidal tract
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Lawrence & Kuypers
1968
Pyramidal tract lesion
Removes key output
from MI direct to
muscles
Lasting deficit in fine
finger movement
Primary motor cortex code for muscle force. Evarts et al., 1968
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Lemon 1988. Spike triggered
averaging
1 MI cell contributes to force
in several muscles (onemany mapping)
Task-specificity
1 MI cell drives a given
muscle in task A but not in
task B
Looks smarter than a
marionette!
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Graziano et al (2002)
Micro-stimulate right M1 (and towards PMC)
Long stimulation (behavioural timescale)
Postures independent of start position
Defensive ‘sensory-relevant’ postures
• “Somatotopic map” is in fact a functional map of different
types of manual behaviour
• Pro: sensorimotor transformation, motor equivalence,
inverse model
• Con: artificial, not physiological, M1 with amputated inputs!
Population coding in MI?
•Each neuron broadly tuned for direction
•Multiple neurons in population
•Population vector predicts movement
direction
(Georgopoulos et al., 1998)
Additional topics
• Task specificity of MI neurons
– Relation to somatotopy
• MI lesions in man
– Hemiplegia
– Psychological consequences: anosognosia
for plegia
• Right hemisphere lesions
• Probably requires parietal damage also
• Anosognosia
• RH damage
• MI AND
Temporoparietal junction