Yuste C12: Motor Planning

Question 1

What does the cortex use to activate spinal cord motor neurons?

Answer 1

Upper motor neurons => voluntary movement

Question 2

Lower motor neurons are controlled by what

Answer 2

Upper motor neurons

Question 3

What does the upper motor system consist of

Answer 3

The cortex, basal ganglia and cerebellum; which control the brainstem and SC motor nuclei.

Question 4

What is notable about the main projection from the upper (cortical) to lower (spinal) motor neurons?

Answer 4

Crossed. Decussates.

Question 5

What is the corticospinal tract

Answer 5

The contralateral pathway connecting the upper motor neurons and the lower motor neurons. AKA the pyramidal pathway.

Question 6

What are pyramidal neurons

Answer 6

Essentially all the excitatory neurons in the cortex whether they are part of the pyramidal pathway or not.

Question 7

Pyramidal pathway is called this why? What does it enable?

Answer 7

Traverse cross section of the cortex shows that we have large pyramid neurons, which reflects the major projection that stretches from the motor cortex straight to the spinal motor neurons that move the muscles in our digits. This projection enables skilled fine movements in our hands and fingers.

Question 8

Is the control of motricity just exerted by the motor cortex talking to the SC?

Answer 8

Besides the pyramidal tract there are other tracts that go from the motor cortex to the reticular formation. The brainstem center is also involved, particularly in postural control, and both the cortex and the brainstem are helped by the basal ganglia and cerebellum.

Question 9

Location of primary motor cortex

Answer 9

Right in front of the central sulcus, which separates the frontal lobe
from the parietal lobe.

It is interesting that the somatosensory cortex is posterior to the central sulcus and the motor cortex is right in front of it.

Question 10

What is special to the motor cortex?

Answer 10

the presence of very large pyramidal cells, the Betz cells.

Question 11

Betz cells

Answer 11

Likely the largest neurons in the body, because their axons begin at the top of the cortex and travel through the spinal cord, where they contact the motor neurons that innervate your limbs. So axons from these neurons could be easily be 1 meter long.

Question 12

How is the motor cortex divided?

Answer 12

divided into the primary motor cortex (M1), the origin of the corticospinal tract, and other motor cortical regions which are known as supplementary motor regions, including also premotor cortex and prefrontal cortex. All of them are involved in motor planning.

Question 13

When do neurons in the primary cortex fire?

Answer 13

neurons fire action potentials when the animal produces a movement, for example as a result of a wrist extension. The firing actually happens just before the animal makes the movement. Once the movement has been made, the motor neuron stops firing.

Question 14

What have experiments using electromyograms shown us?

Answer 14

we see that particular motor neurons fire with the activation of particular muscles. So there is a correlation between specific motor cortex neurons and specific muscles.

Question 15

How does M1 have topography?

Answer 15

Different parts of the M1 are involved in movements of different muscles in our body. Electrical stimulation of different parts of the motor cortex elicits small movements of different parts of the body. We have a motor homunculus.

Question 16

How was the motor map deduced?

Answer 16

Deduced by the neurologist Jackson, as in some epilepsies that progress through the body, the progression is stereotypical and that reflects the physical progression of epilepsy across the motor cortex.

Question 17

How is the motor homunculus different from the somatosensory homunculus?

Answer 17

it has an expanded representation of the parts of the body that generate the majority of useful motor movement. A large representation of our upper extremities (hands in particular). Large part of the motor cortex involved in our tongue (speech). Rest of the body is sort of compressed.

Cf. Heidegger who defined us as the tool makers.

Also, the motor homunculus contains a mixture of neurons within a given territory that might respond to the activation of parts of the body outside of their supposed sections. Also, there are neurons that code for many things at once.

Question 18

What is the interesting principle for neurons in the primary motor cortex

Answer 18

neurons work together in groups. In an experiment with a monkey, researchers recorded the activity of neurons from the arm region of the motor cortex as the monkey was performing a task. Found that many neurons in M1 have directional selectivity, responding to movements only in a particular direction => a tuning curve.
Different neurons have different directional selectivity.

Question 19

What happens when you average the activity of all the neurons in the primary motor cortex

Answer 19

we can precisely predict the movement of the animal! Individual movement is
coded by a population of neurons rather than just one neuron. So it’s not a single neuron that’s doing the job but a joint group of neurons.

Question 20

Motor field

Answer 20

Primary motor neurons have motor fields. The tuning curve of motor neurons.

Question 21

What happens if you lesion the motor cortex neurons

Answer 21

if the pyramidal tract, is lesioned, the monkey can still pick up the food but is not as skilled at performing the task. This suggests that the primary motor cortical neurons are responsible for this fine skill behavior, because if you lesion them you alter/damage the behavior. => pattern of movement becomes disorganized.

Question 22

What happens if you stimulate motor neurons

Answer 22

you trigger funny, non-random movements. These types of movements are very different from the mechanical movements that the spinal cord represents. have biological meaning.

Question 23

Spinal motor neurons vs cortical motor neurons

Answer 23

Spinal motor neurons control the motor units in the muscle, and the muscle is always in the same place, so every time the muscle contracts it performs exactly the same movement. Now the motor cortex is something different – it codes for movement more abstractly.

These movements are more like ideas of movements, goals, or intentions, rather than the actual specification of movement. This suggests that motor cortex is planning and generating the general concept of a movement and sends that information down for someone else to do the job.

Question 24

What happens when we go up the motor hierarchy

Answer 24

We find more abstract properties.

Question 25

Extrinsic kinematics

Answer 25

The goal of the movement

Question 26

Intrinsic kinematics

Answer 26

How you have to move the limbs to achieve that goal.

Question 27

Kinetics

Answer 27

How you have to activate the diff sets of agonist and antagonist muscles to fulfil the intrinsic kinematics.

Question 28

Neurons in premotor and motor areas

Answer 28

if you record from neurons in many different areas, many neurons are doing everything. The ones that are closer to the actual muscle movement are closer to the parietal lobe, computing the kinetics; whereas the further you move from the primary motor cortex, neurons are computing extrinsic kinematics or intention.

for the motor system you don’t have a dissociation of different tasks.

Question 29

What is the premotor cortex connected with?

Answer 29

The premotor cortex is connected very strongly with parts of the parietal cortex which are involved in the ‘where’ pathway.

areas such as premotor cortex and parietal cortex are doing both the somatosensory job and the motor job.

Cf. idea that the brain could be a gigantic neural network

Question 30

Neurons in the premotor cortex

Answer 30

If you record from neurons in the there it turns out that they also have visual and somatosensory receptive fields! These visual and somatosensory fields are actually aligned.

Question 31

What is interesting about what the premotor neurons can fire to?

Answer 31

Premotor neurons can fire to the concept of moving an arm to the right regardless of whether it’s the left arm or the right arm. The premotor cortex has an even more abstract map of ideas of movement and it’s engaging the motor cortex to implement those ideas in a chain of command.

Question 32

What happens if you lesion the supplementary motor cortex

Answer 32

the patient or the monkey stops moving. People who have lesions in the supplementary motor cortex often don’t speak; No will to do so.
Connected to the fact that these acts are voluntary, and this could be generated in these supplementary cortical motor areas.

Question 33

P300

Answer 33

If you record the electrical activity on the frontal lobe of humans in a decision making task, you can detect an event-related potential (ERP) around 300 ms, which correlates with the decision before the subject’s reported conscious awareness that they want to make a movement.

Question 34

Mirror neurons - discovery

Answer 34

Recording from a particular neuron in the premotor cortical area. The neuron fired when the monkey picked up raisins from the table. Another monkey happened to also pick up raisins and the neuron started to fire again. The neuron fired regardless of whether the subject monkey or the other monkey was doing the action. The neuron was also firing when the investigator picked up the raisin.

Question 35

Mirror neurons define

Answer 35

They mirrored the movement of the individual or an action performed by another individual. These neurons are encoding for intention to move. They are encoding the abstract idea of the movement. Present in the premotor area but also in the parietal lobe and prefrontal cortex.

They might also code for other people’s intentions and implement empathy.

Question 36

Mirror neurons and theory of mind

Answer 36

If you have mirror neurons, you could have a model of other minds. These neurons could form representations of the minds of other monkeys or other people. Because of this, mirror neurons could help build a theory of mind—the theory that there is an important social-cognitive skill that allows us to think about the mental states of ourselves and others.

Question 37

Cortical plasticity in the motor cortex

Answer 37

Researchers mapped the area devoted to each finger in the motor cortex. Then they trained the monkey to perform a specific movement: use two fingers at the same time to access the morsel. Motor cortex map changed. The areas that are involved with those two fingers grew; meanwhile areas that responded to the rest of the fingers were reduced.`

Question 38

Brain computer interfaces BCIs

Answer 38

AKA brain machine interfaces, BMIs, neurotechnological devices that connect the brain to a computer.

Question 39

How does a BCI work

Answer 39

Normally, motor information goes from the premotor cortex to primary motor cortex to spinal cord, and a behavior is performed. With a BCI, you record activity from the motor cortex of the patient and directly connect the cortex to a computer. This computer then connects to a prosthetic limb, bypassing the spinal cord. After a training period, she can think about a movement, have that neuronal activity decoded by an algorithm, which sends a command to move the prosthetic limb.

Question 40

BCIs work even though we haven’t deciphered the circuits in the brain

Answer 40

BCI electrodes are inserted essentially at random into the motor cortex, without knowing exactly which are the neurons responsible to initiate the movement. But, even recording from the “wrong” neurons, after some training, the decoding works.

Question 41

Why do BCIs work even if we insert their electrodes essentially at random into the motor cortex

Answer 41

his is likely because of the plasticity associated with the neurons that were probably encoding for something else; due to sensory feedback, they are remapped and learn to code for the prosthetic limbs.

Question 42

Importance of non-invasive BCIs

Answer 42

In principle, you can read and decode cortical activity and connect it to a computer, providing a direct connection from our brain to the net. BCIs can also not only record cortical activity but also stimulate it. Could pipe information into a cortical area and the cortex, with training, sooner or later, would be able to decipher it and use it.

Question 43

How is the motor plan assembled?

Answer 43

The motor plan is assembled in steps, computing intentions (the goals, or “why” move) in prefrontal and parietal cortex, kinematics (the “what” specific movement to generate) in premotor areas, and kinetics (the details of “how” to move the limbs or muscles) in primary motor cortex. These transformations are not just serial but occur in parallel.