1. Motor cortex Organization of motor cortex Motor cortical map
Effect of cortical motor neuron activation on muscle contraction
Population coding

2. Cortical areas involved in motor control
Primary motor cortex (Brodmann’s area 4)
Low intensity stimulation, simple movement
Premotor areas (Brodmann’s area 6)
Premotor cortex
Supplementary motor area
High intensity stimulation, complex movement

3. Evidence for motor cortical map
Jacksonian march (propagation of seizure activity)
Brain stimulation
Intracortical stimulation
TMS (transcranial magnetic stimulation)
Functional MRI

4. Somatotopic map in primary motor cortex
The map is not 100% precise, locally there is both divergence and convergence

5. The map is also highly plastic, use-dependent

6. Primary motor cortex  brain stem  spinal cortex Premotor areas
Major pathways
Primary motor cortex  brain stem  spinal cortex
Premotor areas
 {brain stem  spinal cortex
Layer 5 large pyramidal cells (Betz cells), project to brain stem and spinal cord
Primary motor cortex …

7. Motor cortical neuron and muscle force
Edward Vaughan Evarts (NIH)
developed technique to record from motor cortical neuron from awake monkey performing motor tasks
Motor neuron spiking: force or position?
Fix position, change force

8. Evarts (1968). J. Neurophysiology 31, 14-27
Flexor
load
Flexor
load No
load No
load
Extensor
load
Extensor
load
Activity of a
layer 5 motor neuron
X: extensor EMG
F: flexor EMG

9. Population coding of movement
Georgopoulos et al., 1982

10. Direction tuning of individual neuron
Motor cortical neurons signal both force and direction!

11. Population coding
Vector representation of each motor neuron
vector direction: preferred direction of the neuron
vector length: firing rate during a particular movement
Prediction of movement direction from population activity
Blue: vector representation of individual neurons
Red: vector sum over the population
Yellow: actual movement direction