msc cogneuro lecture 1-2: intro + primary motor cortex (mi)

MSc CogNeuro

Lecture 1-2: Intro

+ Primary Motor Cortex (MI)www.psychol.ucl.ac.uk/patrick.haggard/MSC/msc_1.ppt

Action

• Behaviour

• Movement

• Cognition

• Survival

Brain control to action

• Not conscious

• Computational processes

• Learning

Computational process

• Volition I want to do X• Selection How will I do X?• Initiation Start to do X• Execution Movement towards…• Monitoring Have I got there yet…• Stopping Deactivate X

• NOTE: Process is serial, hierarchical, and information expansion

Computational model of action control(Blakemore, Wolpert, Frith, Trends in Cognitive Science, 2002)

Planner

(Inverse model)

motor commandLimb

Goal/Intention

Forward model

efference copy

sensory feedback

Provisional Road Map (PH)

• A backwards hierarchy– (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

• Fine-grained local somatotopy in MI is quite fractured/overlapping

• 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 representation in the macaque motor cortex: An anatomical perspective. PNAS, 103, 8257-8263

Lateral corticospinal tract (Pyramidal tract)Fine motor control of contralateral musclesKuypers (1968)Corticomotoneuronal cell: 1 synapse from muscle- Cell body in MI, leaves via pyramidal tract

• 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

• Lemon 1988. Spike triggered averaging

• 1 MI cell contributes to force in several muscles (one-many mapping)

• Task-specificity• 1 MI cell drives a given

muscle in task A but not in task B

• Looks smarter than a marionette!

• 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 movementdirection(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