Yuste C13: Motor Selection/Basal Ganglia

Question 1

What is a critical part of behaviour?

Answer 1

the selection of which specific motor program to

activate.

Question 2

What is one serious problem with movement that must be solved

Answer 2

behaviors need to engage one at a

time.

Question 3

Why is there a constant monitoring and alternation of motor patterns?

Answer 3

Need to keep tabs continually on which behavior works and which doesn’t with the current plan, and there are an extremely large number of possibilities of movement. All of this is done on the spot, constantly, right away, while you are moving.

Question 4

What do the basal ganglia and the cerebellum carry out?

Answer 4

Motor selection, motor learning, and motor control. They form two loops that modify the cortico-spinal pipeline.

Question 5

What are the basal ganglia

Answer 5

a collection of nuclei in the diencephalon that essentially form a loop from the cerebral cortex to the thalamus. The basal ganglia are located in the cerebral hemisphere of the forebrain of the CNS. Appeared quite early in evolution.

Question 6

What loop are the basal ganglia involved in

Answer 6

A feedback loop. Information from the cerebral cortex goes to the basal ganglia then to the thalamus before returning to the cortex. This loop starts and ends in the cortex, which tells us that basal ganglia must be involved in the modulation of cortical activity.

Question 7

What are the two main divisions of the basal ganglia

Answer 7

the striatum and the pallidum.

Question 8

What are the two divisions of the striatum

Answer 8

The striatum itself is divided into the caudate and the putamen

Question 9

How is the pallidum divided

Answer 9

the pallidum is divided into the globus pallidus and the substantia nigra.

Question 10

What are the two parts of the substantia nigra

Answer 10

the pars reticulata and the pars compacta.

Question 11

What are the main structures of the basal ganglia

Answer 11

striatum and the pallidum

Question 12

Striatum

Answer 12

Looks striated, because axons are packed into big bundles.

Question 13

Pallidum

Answer 13

looks pale in sections

Question 14

How do different parts of the basal ganglia work

Answer 14

work in different loops with the cerebral cortex.

Question 15

What are the four different anatomical loops that the basal ganglia are involved in

Answer 15

Body movement loop, oculomotor loop, prefrontal loop, limbic loop.

Question 16

The body movement loop

Answer 16

Starts in the motor cortex, right in front of the central sulcus. It projects to the putamen of the striatum, which then projects to the lateral globus pallidus, which projects to the ventral lateral and ventral anterior thalamic nuclei, which then project back up to the central cortical region.

Motor/premotor/somatosensory cortex ==> putamen of striatum ==> globus pallidus of pallidum ==> VA/VL thalamic nuclei (thalamus) ==> motor/premotor/somatosensory cortex.

Question 17

Oculomotor loop

Answer 17

starts in an area within the frontal cortex that is called the frontal eye field. From the frontal eye field, the signal goes to the striatum’s caudate, and from there to the pallidum. The loop continues to the thalamus and returns back to the cortex.

Frontal eye field (cortex) ==> caudate (striatum) ==> globes pallidus, substantial nigra (pallidum) ==> MD, VA thalamic nuclei (thalamus) ==> frontal eye field (cortex).

Question 18

Conclusion from body movement loop and oculomotor loop

Answer 18

the basal ganglia are involved in body and eye movements.

Question 19

The prefrontal loop

Answer 19

The prefrontal cortex is probably calculating the future and evaluating the social environment.
This prefrontal cortex loop also goes first to the striatum, then the pallidum, then the thalamus, and finally returns to the cortex.

Prefrontal ==> putamen ==> globus pallidus, substantia nigra ==> thalamus VA/VL ==> prefrontal.

Question 20

The limbic loop

Answer 20

called the limbic loop, because it comes from the lower part of the frontal lobe; includes the amygdala, hippocampus, orbitofrontal, anterior cingulate, and the temporal cortex.

Amygdala/hippocampus/orbitofrontal/anterior cingulate/temporal ==> ventral striatum ==> ventral pallidum ==> thalamus MD ==> amygdala…

Question 21

Homogeneous design of direct pathway loop.

Answer 21

cortex→ striatum→ pallidum→ thalamus→ back up to the cortex.

Telling us is that basal ganglia are controlling motor behavior, eye movements, whatever the hell is going on in the prefrontal cortex, and the cortical part of our emotional brain. It must be performing the same “canonical” computation, but it is doing so with different cortical regions.

Question 22

What do the areas of the cortex the basal ganglia interact with tell us about the basal ganglia?

Answer 22

The basal ganglia seem to only deal with areas of the cortex anterior of the central sulcus. Everything ahead of the central sulcus is either motor or associated with motor function, including emotions => our interaction with the world.

Question 23

What is the striatum filled with

Answer 23

striatum is filled with the so-called medium spiny neurons receive input from the cortex and project to the globus pallidus and the substantia nigra.

Question 24

Medium spiny neurons connectivity

Answer 24

receive inputs from cortical neurons, and each cortical axon probably connects with only one spine of a given medium spiny neuron; then, the axon continues and connects with another medium spiny neuron, and so on.

Question 25

Why would you design the connectivity between cortical neurons and medium spiny neurons such that each medium spiny neuron would receive info from essentially every cortical neuron and each cortical neuron would talk to essentially every medium spiny neuron?

Answer 25

maximize the distribution of information. This is a design principle we have already seen in olfactory cortex.

Question 26

Why are medium spiny neurons so spiny?

Answer 26

The reason these neurons are super spiny is probably because these dendritic spines are nature’s way to achieve the maximum gathering of inputs.

Question 27

Projection between the cortex and the striatum

Answer 27

every spine represents one axon.; in terms of projections, it’s one to all and all to one.

Question 28

Connection between striatum and pallidum

Answer 28

Each medium spiny neuron is connected to only one pallidal or nigral neuron. It wraps its axon around its dendrites. And each pallidal or nigral neuron is receiving nput from very few striatal neurons. This is more of a 1:1 connection.

in the pallidum, contracting the connectivity, focusing it and funneling all the info into individual cells.

Question 29

Projections from the cortex to the striatum vs from the striatum to the pallidum

Answer 29

the projections from the cortex to the striatum are all excitatory, but the projections from the striatum to the pallidum or substantia nigra are all inhibitory.

Question 30

Projection from pallidum to the thalamus

Answer 30

Inhibitory

Question 31

Projection from the thalamus to the cortex

Answer 31

Excitatory

Question 32

Loop of projections from the cortex to the striatum to the pallidum to the thalamus to the cortex is what kind of circuit

Answer 32

An excitatory circuit built with two inhibitory steps. This is an excitatory loop that has two inhibitory intermediaries.

This is called a disinhibitory circuit. Two sequentially inhibitory neurons in the circuit generate excitation.

Question 33

Pallidum also projects where

Answer 33

To the superior colliculus.

Question 34

Superior colliculus

Answer 34

Particularly engaged for the movements of the eyes and head.

Question 35

What happens to the colliculus when the striatum fires

Answer 35

When the striatum fires, it inhibits the pallidum/substantia nigra, allowing the colliculus to fire. And when the colliculus fires, the monkey makes an eye movement! You can trigger behavior if you stimulate this striatum.

Question 36

How activating the basal ganglia generate targeted eye movements

Answer 36

by disinhibiting the colliculus.

Question 37

Hypothesis regarding the role fo the basal ganglia with the thalamus

Answer 37

basal ganglia are keeping the thalamus shut down all the time; It does not engage the cortex unless something important happens. suggests that it must be extremely important not to activate the wrong behavior. In other words, when you choose to perform a behavior, rather than simply activating it, you have to release it from being clamped.

Question 38

What is new way of considering movement

Answer 38

Moving is an exclusion problem. Behaviors occur one at a time. Suggests that the brain is trigger-happy to generate behavior

Question 39

What is a potential function of the disinhibitory loop

Answer 39

could be to release a particular behavior that has been chosen over all the other behaviors that are ready to jump, in the frontal part of the brain. It’s an example of a winner-take-all algorithm.

Question 40

Shultz and dopamine neurons of the substantia nigra

Answer 40

Shultz was recording from neurons in the substantia nigra of a monkey, who was rewarded for performing the proper movement, whenever their eyes moved toward the proper direction. The neurons in the subtantia nigra stop firing when the monkey makes an eye movement, as they inhibit the colliculus. But, interestingly, when the reward was given, the dopaminergic neurons fired shortly afterwards, as if they coded for the reward. If the reward was unexpected, the neurons fired a lot. The more that the task was learned, the less that the neuron fired to the reward.

Question 41

What are dopaminergic neurons in the substantia nigra coding for?

Answer 41

not just coding for reward, but for the error of reward prediction in terms of reward. If the animal receives a reward but did not expect it, the neurons respond to the “novelty” of the situation by firing. But once the reward is expected, the neurons eventually do not respond. This suggests that these circuits are keeping track of what’s familiar and what’s novel. ==> reward novelty.

Question 42

How is reward novelty related to learning

Answer 42

the basis of reinforcement learning and has to do with predictive coding. If the brain is trying to predict the future, it must be coding for the error between your guess and the reality.

Question 43

Role of basal ganglia and predictive coding

Answer 43

it’s not strictly that you need to engage this loop to perform a behavior, but rather you are opening this loop based on your prediction of what’s going to happen.

Question 44

2 main ideas about the basal ganglia

Answer 44

it has this disinhibitor loop as a way to release a behavior and that it helps calculate the reward prediction error.

Question 45

indirect pathway loop

Answer 45

Cortex→ striatum→ pallidus→ subthalamic nucleus→ pallidus→ thalamus → cortex.

Positive (cortex to striatum), then one negative (striatum to pallidum), then another negative (pallidum to subthalamic), and then a positive (subthalamic to pallidum), and then a third negative (pallidum to thalamus) and a positive (thalamus to cortex). Indirect pathway is inhibitory.

Question 46

Projection from the pallidum to the sub thalamic nucleus and from the STN to the pallidum

Answer 46

The projection from the pallidum to the subthalamic nucleus is inhibitory, while the projection out of the subthalamic nucleus is excitatory.

Question 47

What is one way to think about the direct and indirect pathway

Answer 47

As if the direct pathway were the center and the indirect pathway the surround.

Creating contrast - the basal ganglia enhance the difference in activity between chosen behaviors and unwanted ones.

Question 48

What is a potential purpose for the indirect pathway

Answer 48

could be to create some type of behavioral contrast on the motor plan. Not only do you want to suppress unwanted movements, you want to clamp them. This inhibitory surround makes sure the other behaviors don’t happen.

Question 49

Indirect pathway and contrast

Answer 49

The brain is computing contrast everywhere. if I want to move my middle finger to play the key (the center of this direct pathway), the indirect pathway (surround), at the same time would prevent or clamp down all these other fingers. It could be a way to cleanly do one thing without any interference. Shuts off neighboring behaviors in a computational sense

Question 50

Parkinson’s disease

Answer 50

Pars compacta of the substantia nigra, which has excitatory role. Substantia nigra in Parkinson’s patients is essentially gone. This loss of the dopamine pathways of the substantia nigra reduces the activity of the stratium, which leaves you with a diminished input from the striatum to the pallidum. And because of this diminished input, the pallidum is now less inhibited, which means that the thalamus is more inhibited and there is less excitation to the cortex. Less movement.

Question 51

Huntington’s disease

Answer 51

A striatal degeneration results in a loss of medium spiny neurons in the striatum. Following the indirect pathway, you have this increased activation of the subthalamic nucleus, which generates less inhibition. Through these alterations in the indirect pathway you essentially lose the inhibitory surround. That enhances motor tone.
Example of motor programs that are normally suppressed becoming expressed.

Question 52

Basal ganglia and control theory

Answer 52

What you need to do to build feedback control is to predict the error and make corrections accordingly, planning to minimize that error. This all fits well with the idea that the basal ganglia are one of the brain areas that are involved in reinforcement learning for the brain in terms of motor movements.