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

3. Cortical areas involved in motor control
Primary motor cortex (M1)
- initiation and execution of movement
Premotor and Supplementary motor cortex
- initiation of complex movement, planning the movement
Activity detected in the motor area (by fMRI)
Flexing the finger -- M1 only
Writing a letter with finger (complex sequence of movement) – M1, premotor and supplementary cortex
Think about writing with the finger - premotor and supplementary cortex, not M1.,
(Association cortex)

4. Planning, initiation of voluntary movement
Sensory-motor integration, motor learning
Basic movement, posture
Reflex (involuntary movement)

5. Connections between different motor areas
(integrating all
sensory informatio
(premotor and supplementary motorareas)
Cortico-
spinal tract

6. Stimulation of motor cortex can cause muscle activity
EMG (electromyogram) – recording of muscle contraction activity using extracellular or surface electrode.

7. Evidence for motor cortical map
Intracortical stimulation
Brain stimulation
Intracortical stimulation
TMS (transcranial magnetic stimulation)
Jacksonian march (propagation of seizure activity)
- progressive activation of motor cortex
Functional Brain Imaging (detection of the active brain areas)
Positron Emission Tomography (PET)
-- Detection of activity-related glucose or O2 use by radiation due to positron emission from radioactive non-metabolizable glucose (16O, 18F labeled) or radioactive O2 (16O)
2. Functional Magnetic Resonance Imaging (fMRI)
-- Magnetic resonance resonance of the ratio of oxygenated-nonoxygenated hemoglobin as an indication of increase flow of oxygenated blood flow to the active brain regions.
TMS

8. Somatotopic map in primary motor cortex
Distorted map: disproportionally large representation of parts requiring greater precision
Somatotopic maps also exist in premotor cortex & supplementary motor cortex. Stimulation induces complex movements involving multiple joints and even bilateral movement

9. Divergence and convergence of cortical control of muscles:
-- The same muscle is controlled by several cortical sites
-- One corticospinal axon control many muscles (combinatorial control)
Effectiveness of cortical stimulation at different sites
Experiment:
Microelectrode stimulation over a grid area of motor cortex
Recording from a shoulder muscle (deltoid) and a wrist muscle (ECR)
Finding:
Same muscle can be activated from multiple stimulation sites
Overlap between shoulder and wrist muscle representations
Implication:
Such overlap may allow coordination of multiple muscles for motor tasks

10. Use-dependent plasticity of the motor map
(a) Deprivation causes reduction of representation
Human hand injury
Rat whisker denervation

11. Use-dependent plasticity of the motor map
(b) Practice causes expansion of representation
-- Finger opposition training – touching thumb with finger in a particular sequence. Following 3 weeks of training, fMRI showed larger cortical area activated by performing the trained sequence.
-- fMRI studies showed larger cortical representation of left figures for string player who has an earlier inception of practice, although string players in general have higher representation than non-string players (controls) in the same orchestra.

12. Information coding by motor cortical neurons
In primary motor cortex, neuron fires before movement
Four types of neurons:
Dynamic neuron – code the rate of force
Static neuron – code steady level of force
Mixed neuron – code both rate and level of force
Directional neuron – code for direction of movement
Edward V. Evarts (NIH) developed technique to record from motor cortical neuron from awake monkey performing motor tasks

13. Motor neuron spiking: coding force or position
Motor neuron spiking: coding force or position? Experiment: fix position of movement (wrist rotation), change force applied to the rod
Wrist
Extensor load
Conclusion: Firing of motor cortical neurons codes the force generated by the muscle. This particular neuron recorded activates flexor muscle

14. “Spike triggered average” demonstrate that a single spike from a single motor neuron can exert significant effect on muscle activity
Response correlated with each spike

15. Population coding of movement direction
-Direction of the movement coded by a population of neurons, rather than a single neuron
Experimental setup
Georgopoulos et al., 1982

16. Population coding of movement direction
Actual direction of movement can be predicted by the vector sum of multiple neurons:
Each vector represents one neuron
Vector direction: preferred direction of the neuron
Vector length: firing rate of that neuron during the trial
Direction tuning of individual neuron
Motor cortical neurons signal both force and direction!