striatum and dopamine

Question 1

What are the structures and projection based areas?

Answer 1

Structures - caudate, putamen, nucleus accumbens
Projection based areas - nigrostriatal, mesolimbic

Question 2

What brain areas are often involved in hallucinations?

Answer 2

The sensory cortices - parietal, temporal, occipital
The thalamus

Question 3

What brain areas are often involved in delusions?

Answer 3

The PFC, midbrain and striatum

Question 4

Describe physical/ anatomical signs of schizophrenia

Answer 4

• increased dopamine in the entire striatum system
• increased ventricle size, can increase over time
• cortical thinning -> cells become more densely packed and squished inwards -> loss in projections of thinning areas, not cell less
• caudate size -> initially small (due to lat vent size), then larger relative to age after three years due to D2 blocker antipsychotic drugs

Question 5

What do D2 blockers do to the caudate?

Answer 5

D2 blockers increase the caudate size

Question 6

What does too much dopamine in the caudate and nigrostrital pathways lead to?

Answer 6

Difficulties in goal directed and flexible behaviour - inability to make decisions quickly

Question 7

How do we test goal directed behaviour? What was the finding in mice in this task?

Answer 7

Devalue choice test -> we devalue and option by giving them too much of it, then we present them with an alternative option. They should reasonably choose the other, more ‘valuable’ option.

In mice -> activated DREADDS during the learning or decision phase of the choice test.
- activated during decision - regular bias towards valuable choice/ same as control
- activated during learning - no bias towards valued choice
-> too much dopamine in the striatum did not affect choosing, but affected the ability to learn and integrate the value of a reward

Question 8

What does reversal learning test?

Answer 8

Reactions to reward and loss

Question 9

At what stage of psychosis does a person show deficits in goal directed behaviour?

Answer 9

Persistent psychosis

Question 10

Outline the findings of reversal learning in both early and persistent psychosis.

Answer 10

Early psychosis -> reaction to reward was dependent on the contingency of the task
- showed response to loss
- lose-shift less at 80/40 contingency, but not 80/20
-> consistent with the effect of overloading mice with dopamine (give them amphetamines or activate dopamine pathways)

Persistent psychosis -> reaction to reward was not based on contingency
- showed response to reward
- more likely to shift after a reward (loss of win-stay)
- correlated with poor reversal learning
-> consistent with the effect of little dopamine (inhibit dopamine pathways)