Motor cortex

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