1. From Ch. 38 “Principles of Neural Science”, 4th Ed. Kandel et al
Voluntary Movement
From Ch. 38
“Principles of Neural Science”, 4th Ed.
Kandel et al
May 13, 2009

2. Voluntary movement Voluntary movements are organized in cortex
Sensory feed back
Visual information
Proprioceptive information
Sounds and somatosensory information
Goal of movement
Vary in response to the same stimulus depending on behavioral task (precision vs. power grip)
Improves with learning/ experience
Can be generated in response to external stimuli or internally
May 13, 2009

3. Cortical organization
Hierarchical organization of motor control and task features
Populations of neurons encode motor parameters e.g. force, direction, spatial patterns
The summed activity in a population determines kinematic details of movement
Voluntary movement is highly adaptable
Novel behavior requires processing in several motor and parietal areas as it is continuously monitored for errors and then modified
Primary motor cortex
Fires shortly before and during movement
Fires only with certain tasks and patterns of muscle activation
Premotor areas encode global features of movement
Set-related neurons
Sensorimotor transformations (external environment integrated into motor programs)
Delayed response

4. Motor cortex Primary motor cortex
Activated directly by peripheral stimulation
Executes movements
Adapt movements to new conditions
Premotor areas (different aspects of motor planning)
Dorsal premotor area (dPMA)
Selection of action; Sensorimotor transformations; Externally triggered movements; external cues that do not contain spatial information
Ventral premotor area (vPMA)
Conforming the hand to shape of objects; Mirror neurons; Selection of action; Sensorimotor transformations; Externally triggered movements
Supplementary motor area (SMA)
Preparation of motor sequence from memory (internally not in response to external information)
Pre-supplementary motor area (pre-SMA)
Motor sequence learning
Cingulate motor area (CMA)
Dorsal and ventral portions of caudal and roastral CMA (along the cingulate sulcus)
Functions: to be determined

5. Somatotopical organization
Sequence in human and monkey M1 similar
Face and finger representations are much bigger than others
Greater motor control required for face and fingers
May 13, 2009

6. Motor cortex stimulation
Historical perspective
Discovery of electrical excitability of cortex in the dog; first brain maps (Fritsh and Hitzig)
First motor map of the primate brain (Ferrier)
Recording of extracellular spike activity of a nerve fiber (Adrian)
First experimentally derived human motor map (Penfield and Boldrey)
Microelectrode recordings to map primary somatosensory area (Mountcastle et al.)
First recordings from neurons in awake monkeys (Jasper)
Intracortical microstimulation for mapping of cortical motor output (Asanuma)
TMS is used to activate motor cortex noninvasively (Barker et al.)
1870 electrical stimulation of the cerebral cortex evoked movement in the periphery;
Movements were ordered e.g. stimulation of cortical areas next to each other could evoke movement of fingers in the order they were placed on the hand
1937 Stimulating the human brain with weak electrical shocks in conscious patients during surgery. They later constructed the homunculus showing the real cortical extend of representation of the body.
1985 barker et al developed a new stimulator with the movable hand held coil we know today

7. Transcranial stimulation
TES – transcranial electrical stimulation (Merton and Morton 1980):
High voltage (1-2kV), short duration pulses (10-50us), low resistance electrodes.
Direct stimulation occurs at the anode
Current passes through skin and scalp (resistance) before reaching cortex.
TMS – transcranial magnetic stimulation (Barker 1985)
Discharge of large capacitive currents (5-10kA, 2-300us) through a coil producing high magnetic field (1-2T).
Stimulus site depends on coil design, coil orientation and stimulus intensity
Non-invasive techniques to study
Structure-function relationship (e.g. rTMS virtual lesion)
Map brain motor output (typically averaged EMG as output =MEP)
Measure conduction velocity
TMS has advantages over TES
No discomfort (no current passes through skin and high current densities can be avoided)
No attenuation of field when passing through tissue
No skin preparation (conduction gel)
TES: short duration reduces discomfort of electroshock
Big electrodes (5-10cm) ensures no tissue damage by creating low current densities
Anode should be placed over the site to be stimulated. Cathode indifferent site

8. Transcranial magnetic stimulation
Principles of TMS
Coil design
B Field decays as the square of distance from coil
Faraday’s law B field induces am electric field E which induces a current in cortex
Current is parallel to the place of the coil and flowing in opposite direction of the current in the coil
The electric field affects the membrane potential which depolarizes mostly at axon curvatures.
May evoke muscle contractions, sensory perceptions, or behavioural changes e.g. antidepressant
COIL: figure-8 coil most commonly used because it produces a more focal area of stimulation

9. Motor cortex stimulation
Movements can be evoked by direct stimulation of motor cortex
Activates corticospinal fibers
Direct from motor cortex to spinal motor neurons or interneurons
Evokes a short latency EMG response in contralateral muscles
Latency depends on corticospinal distance impulses have to travel
Latency difference
May 13, 2009

10. Cortex-muscle connections
Shoulder muscle
Wrist muscle
Maps can be generated by intracortical microstimulation
Sites controlling individual muscles are distributed over a wide area of motor cortex
Muscle representations overlap in cortex
Stimulation of single sites activates several muscles (diverging innervation)
Many motor cortical neurons contribute to multijointed movements
May 13, 2009

11. Motor cortex Primary motor cortex
Activated directly by peripheral stimulation
Executes movements
Adapt movements to new conditions
Premotor areas (different aspects of motor planning)
Dorsal premotor area (dPMA)
Selection of action; Sensorimotor transformations; Externally triggered movements; external cues that do not contain spatial information
Ventral premotor area (vPMA)
Conforming the hand to shape of objects; Mirror neurons; Selection of action; Sensorimotor transformations; Externally triggered movements
Supplementary motor area (SMA)
Preparation of motor sequence from memory (internally not in response to external information)
Pre-supplementary motor area (pre-SMA)
Motor sequence learning
Cingulate motor area (CMA)
Dorsal and ventral portions of caudal and roastral CMA (along the cingulate sulcus)
Functions: to be determined

12. Cortical projections
Premotor cortex and primary motor cortex has reciprocal connections
Parietal projections to premotor areas (sensorimotor transformations)
Prefrontal projections to some premotor areas (cognitive-affective control and learning)
Premotor areas and primary motor areas have direct projections to spinal motor neurons
May 13, 2009

13. Other projections Inputs from cerebellum Inputs from basal ganglia
Do not project directly to spinal cord
Inputs from basal ganglia
Cortico-striatal pathways
Motor loops
Motor cortex => striatum => globus pallidus => Thalamus => motor cortex
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14. Motor cortex plasticity
The functional organization of M1 changes after transection of facial nerve
May 13, 2009

15. Practiced movements PET data
M1 representation becomes more dense with practice
PET data
May 13, 2009

16. Pyramidal tract
Successive cortical stimuli result in progressively larger EPSP in spinal motor neurons
Make it possible to make individual movement of digits and isolated movements of proximal joints
Direct corticospinal control is necessary for fine control of digits
Bilateral sectioning of the pyramidal tract removes the ability if fine movements
May 13, 2009

17. Ia spinal circuits Spinal Ia neurons are inhibitory interneurons
Can respond directly to changes in somatosensory input
Cortical centers do not need to respond to minor changes
The Ia inhibitory neurons in the spinal cord sends inhibitory signals to antagonist motor neurons when muscle spindles in the agonist muscle are activated
Ia neurons also inhibits spinal reflexes
Spinal circuits are used as components of complex behaviors
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18. Direction of movement
Increased activity with load
Wrist displacement constant but load is different
Activity in individual neurons in M1 is related to muscle force and not direction
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19. Postspike facilitation
Spike-triggered averaging
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20. M1 and force
Linear relationship between M1 firing rate and force generation
Two types of motor cortical neurons
Phasic-tonic: initial dynamic burst
Tonic: tonic high level
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21. Direction of movement
Single neuron
Population vector
Predicted from vector
Actual movement
Direction of movement is encoded by a population of neurons
Motor cortical neurons are broadly tuned to directions but have a preferred direction
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22. Direction of movement
M1 encoding of force required to maintain a direction
Single
Arm movements without and with external loads
Unloaded: preferred direction to the upper left
Loaded: opposite, preferred direction to the lower right
A cells firing rate increases if a load opposes movement in preferred direction and decreases if load pulls in preferred direction
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23. Activity depends on motor task
Precision grip: same activity whether force is light or heavy
Power grip: No activity, but EMG activity the same
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24. Complexity of movement
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25. Internal and external information
Influence on visual cue and prior training in motor cortex
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26. Motor preparation Dorsal premotor area is active during preparation
Fires according to different delay times
Fires during the whole period of anticipation
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27. Visuomotor transformations
Separate but parallel fronto-parietal projections
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28. Ventral premotor cortex
Specific hand tasks activate vPMC
May 13, 2009

29. Mirror neurons Precision grip Observed movement
Ventral premotor area
Precision grip
Observed movement
Observed human movement
Self-performed movement
May 13, 2009

30. Summary Hierarchical organization of motor control and task features
Populations of neurons encode motor parameters e.g. force, direction, spatial patterns
The summed activity in a population determines kinematic details of movement
Voluntary movement is highly adaptable
Novel behavior requires processing in several motor and parietal areas as it is continuously monitored for errors and then modified
Primary motor cortex
Fires shortly before and during movement
Fires only with certain tasks and patterns of muscle activation
Premotor areas encode global features of movement
Set-related neurons
Sensorimotor transformations (external environment integrated into motor programs)
Delayed response