L23 - Classic Basal Ganglia Model

Question 1

Rapid decision making is based upon our ________

Answer 1

Past Experiences

Question 2

What factors about our past experiences influence our decision making?

Answer 2

Consequences: Rewards or Punishments

Question 3

Decision making is based on what ability (or inability)

Answer 3

to delay gratification

(if we cant we become impulsive, this is ADHD)

Question 4

The “classical basal ganglia model” of decision making is what type of model?

Answer 4

Neurobiological

Question 5

What part of our brain is responsible for “transmitting messages”

Answer 5

Neurons

Question 6

What happens when a neuron receives a message that is strong enough for it to be transmitted?

Answer 6

An action potential is generated

Question 7

A neurotransmitter does what?

Answer 7

Transmits a chemical message from the presynaptic neuron to the postsynaptic neuron

Question 8

Do neurons “touch” each other?

Answer 8

No, there is a gap in between them

Question 9

How might a “message” from a presynaptic neuron be broken?

Answer 9

If the postsynaptic neuron does not have the appropriate receptors or it is blocked somehow.

e.g. neurotransmitter is dopeamine but receptor does not have dopeamine receptors or is blocked

Question 10

What is GABA?

Answer 10

Gamma-Aminobutyric Acid (GABA)

The major inhibitory neurotransmitter in the central nervous system

Question 11

What is Glutamate?

Answer 11

Major excitatory neurotransmitter in the central nervous system

Question 12

What are the names of the major inhibitory and excitatory neurotransmitters?

Answer 12

GABA - inhibitory

Glutamate - Excitatory

Question 13

If a postsynaptic neuron has GABA receptors and GABA is released from the presynaptic neurons, what happens?

Answer 13

The effect of the neurotransmitter will be to make the neuron less likely to perform an action potential

inhibitory neurotransmittor

Question 14

If a postsynaptic neuron has Glutamate receptors and Glutamate is released from the presynaptic neurons, what happens?

Answer 14

It will excite the postsynaptic neuron

Excitatory

Question 15

If you want to inhibit a postsynaptic neuron, what chemical can you use to do this?

Answer 15

GABA

Question 16

According to the classic basil ganglia model

Does a neuron which recieves an excitatory message pass on the excitatory message to other neurons?

Answer 16

Not necessarily, some neurons recieve an excitatory neuron (glutamate) and get excited, but then they release GABA to stop other ‘messages’ coming from the presynaptic neuron after it

some neurons are design to inhibit other neurons, even when recieving excitatory neurotransmitters

Question 17

Describe the classical basal ganglia model of action selection

Answer 17

1. Pre-motor cortex generates pre-action plans
2. Send action plans to the basal ganglia through excitatory connections
3. basal ganglia decides whether to accept/reject action plan
4. If accepted, basal ganglia sends output to the thalamus, which disinhibits the thalamus
5. Motor command is then performed

Question 18

What is the basal ganglia?

Answer 18

a collection of interconnected nuclei in the midbrain) that ‘select’ or ‘inhibit’ a motor plan

acts as a gate that can say yes or no to the action plans that the cortex generates

Question 19

When is a motor command performed according to the basal ganglia action model?

Answer 19

When the basal ganglia disinhibits the thalamus

Question 20

What is the normal state of the thalamus?

Answer 20

Constant ‘Tonic’ Inhibition

Constantly inhibited - this prevents any motor command being performed

Question 21

Cortex Creates Potential Actions - Basal Ganglia Selects Actions - Basal Ganglia Disinhibits Thalamus

What does this do?

What model are these three steps from?

Answer 21

Generates an action

The classical basal ganglia model of action selection

Question 22

What would happen if the thalamus was not constantly inhibited?

Answer 22

We would constantly be doing random actions

We would have no control over our bodies

Question 23

What does the basal ganglia do to the thalamus to generate a motor command?

What is this pathway called that is responsible for this?

Answer 23

Disinhibits the thalamus

The Direct Pathway

Question 24

What does the indirect ‘no-go’ pathway do?

Answer 24

If this pathway is activated, it further inhibits the thalamus, to make certain that the action is not performed

Question 25

What region of the brain is responsible for the 'no-go' pathway?

Answer 25

Basal Ganglia *same as direct pathway*

Question 26

The **direct** pathway 1)\_\_\_\_\_ the thalamus, while the **indirect** pathway 2)\_\_\_\_\_ the thalamus.

Answer 26

**1) disinhibits** **2) further inhibits**

Question 27

What level of inhibition is the thalamus typically at without the influence of the basal ganglia?

Answer 27

weak inhibition

Question 28

Name the two pathways of the classical basal ganglia model and what they are responsible for

Answer 28

Direct "go" pathway - select motor command Indirect 'no-go' pathway - inhibit motor command

Question 29

In the classical basal ganglia model, what is the "critical point of difference" of each pathway?

Answer 29

The Striatum

Question 30

What is the importance of the Striatum?

Answer 30

This is where the two pathways diverge in the basal ganglia

Question 31

How does the **striatum** operate?

Answer 31

It has **two distinct populations of neurons** (excitatory and inhibitory) When the cortex sends a message to the striatum, the type of neuron that is released from the striatum will determine whether the action is performed. *The neurons are competing with each other, one trying to make it happen and one trying to inhibit it*

Question 32

How does the striatum determine what population of neurons are released?

Answer 32

**Our** **previous experience** *These neurons have learnt from our previous experiences*

Question 33

Where are our memories of what has happened in the past stored according to the classic basal ganglia model for action?

Answer 33

In the population of neurons in our striatum

Question 34

How does the striatum learn from our previous experiences to **generate** motor actions?

Answer 34

If we recieve a reward we recieve an **increase in dopamine** - this strengthens direct pathway connections - actions are more likely to be repeated in the future

Question 35

How does the striatum learn from our previous experiences to **inhibit** motor actions?

Answer 35

If we recieve punishment we get a **decrease** in dopamine activity - this strengthens the indirect pathway connections - actions are less likely to be repeated in the future

Question 36

What happens to the stratium when you recieve a **drop** in neurons? When does this happen and what is the likely future outcome?

Answer 36

**Indirect pathway** connections are strenghtened You have been punished and are less likely to perform that action

Question 37

What happens to the stratium when you recieve a **increase** in neurons? When does this happen and what is the likely future outcome?

Answer 37

**Direct** pathway connections are strenghtened You have been **rewarded** and are **more** likely to perform that action

Question 38

How many dopamine receptors are there?

Answer 38

5 (D1-D5)

Question 39

Dopamine D1 receptors have what type of sensitivity to dopamine? What does this mean?

Answer 39

Low sensitivity *(They have low affinity to dopamine)* In order for them to be activated they need to recieve a large burst of dopamine

Question 40

What is the primary use of the D1 receptors?

Answer 40

To detect dopamine bursts from reward Critical for learning in the direct pathway neurons

Question 41

What is **D1-mediated long-term potentiation**?

Answer 41

A type of neuroplasticity that strengthens the synapses, or connections, between neurons, so ‘messages’ between them are transmitted more efficiently

Question 42

What does a burst in dopamine result in?

Answer 42

D1-mediated long-term potentiation

Question 43

What is **long-term potentiation?** How does it work?

Answer 43

**Long-term potentiation is a type of synaptic plasticity that increases the efficacy of neurotransmission.** Repeated synchronous firing increases the strength of the connections between two neurons.

Question 44

What is synaptic plasticity?

Answer 44

Presynaptic transmitters and postsynaptic recievers can increase in strength if it is used repeatedly, allowing for more information to pass through. *After repeated firing the presynaptic and postsynaptic neurons change to allow for more information to pass through (long-term potentiation)*

Question 45

What type of affinity (sensitivity) do **dopamine D2** **receptors** have? What does this mean

Answer 45

High affinity for dopamine Low levels of dopamine activate them; high levels inhibit them

Question 46

What happens to **dopamine D2 receptors** when a high amount of dopamine is recieved?

Answer 46

They shut off *only responsive to low levels of dopamine*

Question 47

Repeated dopamine dips result in what?

Answer 47

D2-mediated long-term potentiation *less likelihood to perform action*

Question 48

When you are punished, which dopamine receptors are activated and why?

Answer 48

D2 receptors When you are punished it results in a dopamine "dip" and release less dopamine - D2 receptors are the only receptors that will activate then due to their high sensitivity to dopamine

Question 49

Where is DNA located?

Answer 49

Inside every cell contains a nucleus In the nucleus is DNA

Question 50

What is a good metaphor for DNA and genes?

Answer 50

They are a **recipe book** Cells open up the recipe book to find the gene it needs to use and uses it

Question 51

How many genes in our DNA?

Answer 51

Roughly 20,000

Question 52

How does a cell produce a protein?

Answer 52

Unfold our DNA, read the DNA (like a book) and produce the protein it needs

Question 53

How does a neuron replace a receptor or increase a receptor?

Answer 53

Unfold the DNA for the receptor, produce the relevent gene, create the receptor

Question 54

The **DRD1 gene** is a gene that contains the recipe for what?

Answer 54

The **dopamine D1 receptor**

Question 55

The **DRD2 gene** is a gene that contains the recipe for what?

Answer 55

Dopamine D2 receptor

Question 56

Are all cells able to express DRD1 and DRD2 genes?

Answer 56

No *Not all cells use the recipes to produce these types of receptors*

Question 57

What does "cells having a preference for genes" mean?

Answer 57

That some cells are more likely to express genes than others *e.g. some are more likely to express DRD1 whereas others DRD2*

Question 58

The indirect pathway has more __ receptors

Answer 58

D2 receptors

Question 59

The **direct** pathway has more __ receptors

Answer 59

D1

Question 60

What is the benefit of the indirect and direct cells having preferences for DRD1 or DRD2 genes?

Answer 60

That they become more efficient at detecting the dopamine levels and better at producing/inhibiting actions

Question 61

What basal ganglia pathway is responsible for "impulsivity"

Answer 61

Direct pathway

Question 62

Which striatum pathway is responsible for the delay of gratification and resisting impulses?

Answer 62

indirect 'no-go' pathway

Question 63

Everyone is similar when it comes to our ability to learn from reward and punishment. True or False

Answer 63

False Some people learn more from punishment than from reward and vice versa

Question 64

"Punishment learners" are _____ at resisting temptation

Answer 64

Better

Question 65

"Go" pathway learners learn better from 1)\_\_\_\_\_\_ than 2) \_\_\_\_\_\_

Answer 65

1) Rewards 2) Punishment * "Go" pathway learners learn better from 1)\_\_\_\_\_\_ than 2) \_\_\_\_\_\_*