L23 - Classic Basal Ganglia Model Flashcards
Rapid decision making is based upon our ________
Past Experiences
What factors about our past experiences influence our decision making?
Consequences: Rewards or Punishments
Decision making is based on what ability (or inability)
to delay gratification
(if we cant we become impulsive, this is ADHD)
The “classical basal ganglia model” of decision making is what type of model?
Neurobiological
What part of our brain is responsible for “transmitting messages”
Neurons
What happens when a neuron receives a message that is strong enough for it to be transmitted?
An action potential is generated
A neurotransmitter does what?
Transmits a chemical message from the presynaptic neuron to the postsynaptic neuron
Do neurons “touch” each other?
No, there is a gap in between them
How might a “message” from a presynaptic neuron be broken?
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
What is GABA?
Gamma-Aminobutyric Acid (GABA)
The major inhibitory neurotransmitter in the central nervous system
What is Glutamate?
Major excitatory neurotransmitter in the central nervous system
What are the names of the major inhibitory and excitatory neurotransmitters?
GABA - inhibitory
Glutamate - Excitatory
If a postsynaptic neuron has GABA receptors and GABA is released from the presynaptic neurons, what happens?
The effect of the neurotransmitter will be to make the neuron less likely to perform an action potential
inhibitory neurotransmittor
If a postsynaptic neuron has Glutamate receptors and Glutamate is released from the presynaptic neurons, what happens?
It will excite the postsynaptic neuron
Excitatory
If you want to inhibit a postsynaptic neuron, what chemical can you use to do this?
GABA
According to the classic basil ganglia model
Does a neuron which recieves an excitatory message pass on the excitatory message to other neurons?
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
Describe the classical basal ganglia model of action selection
- Pre-motor cortex generates pre-action plans
- Send action plans to the basal ganglia through excitatory connections
- basal ganglia decides whether to accept/reject action plan
- If accepted, basal ganglia sends output to the thalamus, which disinhibits the thalamus
- Motor command is then performed
What is the basal ganglia?
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
When is a motor command performed according to the basal ganglia action model?
When the basal ganglia disinhibits the thalamus
What is the normal state of the thalamus?
Constant ‘Tonic’ Inhibition
Constantly inhibited - this prevents any motor command being performed
Cortex Creates Potential Actions - Basal Ganglia Selects Actions - Basal Ganglia Disinhibits Thalamus
What does this do?
What model are these three steps from?
Generates an action
The classical basal ganglia model of action selection
What would happen if the thalamus was not constantly inhibited?
We would constantly be doing random actions
We would have no control over our bodies
What does the basal ganglia do to the thalamus to generate a motor command?
What is this pathway called that is responsible for this?
Disinhibits the thalamus
The Direct Pathway
What does the indirect ‘no-go’ pathway do?
If this pathway is activated, it further inhibits the thalamus, to make certain that the action is not performed
What region of the brain is responsible for the ‘no-go’ pathway?
Basal Ganglia
same as direct pathway
The direct pathway 1)_____ the thalamus, while the indirect pathway 2)_____ the thalamus.
1) disinhibits
2) further inhibits
What level of inhibition is the thalamus typically at without the influence of the basal ganglia?
weak inhibition
Name the two pathways of the classical basal ganglia model and what they are responsible for
Direct “go” pathway - select motor command
Indirect ‘no-go’ pathway - inhibit motor command
In the classical basal ganglia model, what is the “critical point of difference” of each pathway?
The Striatum
What is the importance of the Striatum?
This is where the two pathways diverge in the basal ganglia
How does the striatum operate?
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
How does the striatum determine what population of neurons are released?
Our previous experience
These neurons have learnt from our previous experiences
Where are our memories of what has happened in the past stored according to the classic basal ganglia model for action?
In the population of neurons in our striatum
How does the striatum learn from our previous experiences to generate motor actions?
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
How does the striatum learn from our previous experiences to inhibit motor actions?
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
What happens to the stratium when you recieve a drop in neurons?
When does this happen and what is the likely future outcome?
Indirect pathway connections are strenghtened
You have been punished and are less likely to perform that action
What happens to the stratium when you recieve a increase in neurons?
When does this happen and what is the likely future outcome?
Direct pathway connections are strenghtened
You have been rewarded and are more likely to perform that action
How many dopamine receptors are there?
5
(D1-D5)
Dopamine D1 receptors have what type of sensitivity to dopamine?
What does this mean?
Low sensitivity
(They have low affinity to dopamine)
In order for them to be activated they need to recieve a large burst of dopamine
What is the primary use of the D1 receptors?
To detect dopamine bursts from reward
Critical for learning in the direct pathway neurons
What is D1-mediated long-term potentiation?
A type of neuroplasticity that strengthens the synapses, or connections, between neurons, so ‘messages’ between them are transmitted more efficiently
What does a burst in dopamine result in?
D1-mediated long-term potentiation
What is long-term potentiation?
How does it work?
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.
What is synaptic plasticity?
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)
What type of affinity (sensitivity) do dopamine D2 receptors have?
What does this mean
High affinity for dopamine
Low levels of dopamine activate them; high levels inhibit them
What happens to dopamine D2 receptors when a high amount of dopamine is recieved?
They shut off
only responsive to low levels of dopamine
Repeated dopamine dips result in what?
D2-mediated long-term potentiation
less likelihood to perform action
When you are punished, which dopamine receptors are activated and why?
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
Where is DNA located?
Inside every cell contains a nucleus
In the nucleus is DNA
What is a good metaphor for DNA and genes?
They are a recipe book
Cells open up the recipe book to find the gene it needs to use and uses it
How many genes in our DNA?
Roughly 20,000
How does a cell produce a protein?
Unfold our DNA, read the DNA (like a book) and produce the protein it needs
How does a neuron replace a receptor or increase a receptor?
Unfold the DNA for the receptor, produce the relevent gene, create the receptor
The DRD1 gene is a gene that contains the recipe for what?
The dopamine D1 receptor
The DRD2 gene is a gene that contains the recipe for what?
Dopamine D2 receptor
Are all cells able to express DRD1 and DRD2 genes?
No
Not all cells use the recipes to produce these types of receptors
What does “cells having a preference for genes” mean?
That some cells are more likely to express genes than others
e.g. some are more likely to express DRD1 whereas others DRD2
The indirect pathway has more __ receptors
D2 receptors
The direct pathway has more __ receptors
D1
What is the benefit of the indirect and direct cells having preferences for DRD1 or DRD2 genes?
That they become more efficient at detecting the dopamine levels and better at producing/inhibiting actions
What basal ganglia pathway is responsible for “impulsivity”
Direct pathway
Which striatum pathway is responsible for the delay of gratification and resisting impulses?
indirect ‘no-go’ pathway
Everyone is similar when it comes to our ability to learn from reward and punishment.
True or False
False
Some people learn more from punishment than from reward and vice versa
“Punishment learners” are _____ at resisting temptation
Better
“Go” pathway learners learn better from 1)______ than 2) ______
1) Rewards
2) Punishment
* “Go” pathway learners learn better from 1)______ than 2) ______*
