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Neural Basis of Movement > L8 - Basal Ganglia and Reinforcement > Flashcards

L8 - Basal Ganglia and Reinforcement Flashcards

1
Q

Where does the Basal Ganglia sit in the brain?

A

In the middle, under the cerebral cortex

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2
Q

What is the function of the Basal Ganglia?

A

To select appropriate movements. Acts as a filter for all the different possible actions and then picks the preferred one and sends it to the cortex to be executed.

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3
Q

What does the basal ganglia consist of?

A

Several different nuclei:

  • Striatum
  • Globus Pallidus (GP)
  • Subthalamic Nucleus
  • Substantia Nigra (SN)
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4
Q

The basal ganglia is characterised by what?

A

Direct and indirect pathways.

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5
Q

Describe an overview of the direct and indirect pathways between the cortex and basal ganglia.

A
  • The cortex projects to the spinal cord and striatum.
  • The striatum projects directly to the Substantia Nigra (SNr) and Globus Pallidus (GPi), which is a composite structure.
  • This composite structure then projects to the thalamus or the brain stem/superior colliculus.
  • The striatum can also project indirectly to the external Globus Pallidus (GPe), which then projects to the Subthalamic Nucleus (STN).
  • The STN then projects to the SNr-GPi structure, from which the regular loop continues.
  • The thalamus projects back to the cortex.
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6
Q

Describe the inhibitory and excitatory sections of the direct and indirect pathways.

A

Direct:
Cortex excites the striatum.
Striatum inhibits the SNr-GPi
The SNr-GPi therefore is less active in inhibiting the thalamus, meaning the thalamus is more active.
The thalamus therefore excites the cortex

Indirect:
Cortex excites the striatum
Striatum inhibits the GPe
GPe is less active in inhibiting the STN, meaning the STN is more active.
STN excites the SNr-GPi
SNr_GPi inhibits the thalamus
Thalamus excites the cortex less
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7
Q

Which pathway from the cortex through the basal ganglia is excitatory and which is inhibitory?

A

Direct ‘go’ pathway is excitatory

Indirect pathway is inhibitory.

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8
Q

What does SNc stand for?

A

Substantia nigra compacter

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9
Q

Where does the SNc project to?

A

The striatum

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10
Q

What does the SNc do?

A

Projects dopamine into the striatum

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11
Q

Why are there both excitatory and inhibitory links between the SNc and the striatum?

A

Because the striatum has both excitatory receptors (D1) and inhibitory receptors (D2).

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12
Q

What would happen if you had low levels of dopamine and why?

A

Reduced movement. This is due to the weakening of the direct pathway and the strengthening of the indirect pathway.

The weakening of the direct pathway occurs because D1 receptors in the striatum are not being excited.
At the same time, D2 receptors in the striatum are being less inhibited, meaning that the whole indirect pathway strengthens, which has an inhibitory effect on the thalamus.

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13
Q

In Parkinson’s disease, which structure is damaged/targeted, causing large numbers of cell death?

A

Substantia Nigra compacter, resulting in reduced input of dopamine into the striatum.

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14
Q

What percentage of cells in the Substantia Nigra needs to die in order to start presenting with symptoms of Parkinson’s disease?

A

70%-80%

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15
Q

Is striatal damage symmetrical? Explain how we know.

A

No, PET studies have shown that uptake of tracers is asymmetrical, it starts to reduce in one side of the striatum more than the other.

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16
Q

What are the 3 cardinal symptoms of Parkinson’s?

A
  • Absence/slowness of movement (Akinesia/bradykinesia) - hypokinetic
  • Stiffness or rigidity
  • Tremor ‘at rest’ (hyperkinetic)
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17
Q

What are some of the other symptoms of Parkinson’s?

A
  • Gate disturbances (walk with small step sizes)
  • Postural stoop
  • Mask-like face, not as much expression
  • Depression
  • Speech and swallowing difficulties
  • Mental confusion
  • Sleep disturbances
  • Loss of sense of smell.
18
Q

How many of the cardinal symtpoms must one have to be considered/diagnosed with Parkinson’s Disease?

A

All 3

19
Q

What does PD stand for?

A

Parkinson’s Disease

20
Q

What are 3 of the main treatments for Parkinson’s disease?

A
  • Inject Levadopa, pre-cursor for dopamine
  • Transplants to replace damaged cells/areas.
  • Neurosurgery to rebalance connections between the striatum and SMA.
21
Q

Why can dopamine not be used to inject into and treat people with PD?

A

It cannot pass the blood-brain barrier.

22
Q

When might levodopa induced dyskinesia’s occur?

A

Long term levodopa intolerance

23
Q

What are dyskinesia’s?

A

Movements that are unwanted and uncoordinated.

24
Q

Why do levodopa induced dyskinesia’s occur?

A

Excess dopamine input after long term levodopa treatment causes the direct pathway to become too strong and the indirect pathway too weak.

25
Q

In early Huntington’s Disease, which pathway is most affected?

A

The indirect pathway

26
Q

What are choreas?

A

Complex, dance-like movements which may occur due to imbalances in the striatal pathway.

27
Q

What is HD?

A

Huntington’s Disease

28
Q

What is HD caused by?

A

Degeneration of neurons in the striatum.

29
Q

What is the mechanism by which degeneration of striatal neurons occur, due to HD?

A

A mutation occurs causing excess calcium to enter the striatum. This is a highly energy demanding process, leaving cells to die due to insufficient energy.

30
Q

How might the basal ganglia influence eye movement?

A
  • It can activate certain sites in the superior colliculus to allow certain stimuli to be attended to through saccades.
  • It can decide which voluntary eye movements to make
  • It can inhibit certain saccades.
31
Q

What are the different learning systems of the cortex, basal ganglia and cerebellum?

A
  • Cortex: learning relationships (classical)
  • Basal Ganglia: Reinforcement learning (operant)
  • Cerebellum: Learning through error correction
32
Q

What are the 3 natural reinforcers, and what happens when we are able to get them?

A

Water, food and sex. When we drink, eat and have sex, dopamine is released.

33
Q

What type of reinforcers are humans more concerned with than other species?

A

Secondary reinforcers - e.g. money. Money itself will not lead to a reward, but more the expectation of a reward - more water, nicer food, etc.

34
Q

What does ICSS stand for?

A

Intra-cranial self stimulation

35
Q

What is the mechanism behind reinforcement and dopamine when using ICSS?

A
  • ICSS causes dopamine release in the Nucleus accumbens/striatum/cortex, which leads to a rewarding effect.
  • This dopamine release potentiates glutamate transmission in the cortex, leading to the strengthening of cortical inputs to the striatum.
  • LTP in synapses occur, leading to long term reinforcement of behaviour - meaning that the action(s) is still performed even when no longer rewarding (addiction)
36
Q

What can optogenetics achieve and how does it achieve it?

A

Can activate either the direct or indirect pathway on it’s own, by shining light on striatal neurons with light sensitive proteins.

37
Q

How sensitive would a PD patient be to reward?

A

Less sensitive than normal/without PD. (why?)

38
Q

What is better for long term learning - reward or punishment?

A

Reward

39
Q

What is better for short term learning - reward or punishment?

A

Punishment

40
Q

What are the inputs to the basal ganglia?

A

Sensory-motor, limbic and cognitive.

Neural Basis of Movement (10 decks)

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