Reinforcement and the striatum

Question 1

Define a drive.

Answer 1

An innate, biologically determined urge to achieve a goal or satisfy a need.

Question 2

Define reinforcement.

Answer 2

The process of strengthening an organisms future behaviour.

Question 3

What drives reinforcement?

Answer 3

Reward: stimuli that increase the probability of particular behaviour.

Question 4

Define an appetitive reinforcement.

Answer 4

The reward is a positive stimulus, e.g. food.

Question 5

Define aversive reinforcement.

Answer 5

The reward is a negative stimulus, e.g. pain.

Question 6

What are the reward/reinforcement areas in the brain thought to be?

Answer 6

The ventral striatum, particularly the nucleus accumbens.

Question 7

The ventral striatum is part of the basal ganglia complex. This is composed of 5 individual nuclei in primates. What are they?

Answer 7

1. Striatum
2. External segment of globus pallidus (GPe)
3. Internal segment of globus pallidus (GPi)
4. Subthalamic nucleus (STN)
5. Substantia nigra (SN)

Question 8

There are 2 midbrain dopamine pathways. What are they?

Answer 8

1. The mesolimbic pathway

2. The mesocortical pathway

Question 9

What structures are included in the mesolimbic pathway?

Answer 9

The VTA, the amygdala, the hippocampus and the nucleus accumbens (there are others but I won’t remember them).

Question 10

What are disorders in the mesolimbic pathway associated with?

Answer 10

Faulty reward and reinforcement behaviour.

Question 11

What structures are included in the mesocortical pathway?

Answer 11

The VTA, prefrontal cortex and hippocampus (there are others but I won’t remember them).

Question 12

What are disorders of the mesocortical pathway associated with?

Answer 12

Schizophrenia.

Question 13

What happens in the nucleus accumbens when the VTA is stimulated by an electrode?

Answer 13

Dopamine levels increase.

Question 14

What happens in the nucleus accumbens when a subject is presented with food?

Answer 14

Dopamine levels increase.

Question 15

What happens in the nucleus accumbens during sex?

Answer 15

Dopamine levels almost double in rats.

Question 16

Do nicotine and cannabis cause elevated dopamine levels in the nucleus accumbens?

Answer 16

Yes.

Question 17

What is the point of self-administration experiments?

Answer 17

To see whether the subject likes a drug and look at which brain areas are stimulated during drug use.

Question 18

What effect do cocaine and amphetamine have on dopamine levels in the nucleus accumbens?

Answer 18

Increased dopamine levels.

Question 19

What effect did using a dopamine blocker have in self-administration experiments?

Answer 19

The rat kept administering more and more drug, trying to achieve the sense of reward afforded by dopamine release.

Question 20

What happened in self-administration experiments of cocaine when the animal had lesions to the nucleus accumbens?

Answer 20

The self-administration was greatly reduced. The nucleus accumbens could not properly release dopamine so no ‘reward’ was felt.

Question 21

What do heroin and morphine act on within the body?

Answer 21

Endogenous opioid receptors.

Question 22

What is the natural function of endogenous opioids?

Answer 22

To supress pain, a survival technique.

Question 23

Injecting opiates has what affect on dopamine in the nucleus accumbens?

Answer 23

Increased levels.

Question 24

What happens to self administration of opioids if there are lesions to the nucleus accumbens?

Answer 24

Self-administration does NOT reduce, suggesting there must be a different pathway for opioid action.

Question 25

What is thought to be the pathway for opioids in the body?

Answer 25

They act in the VTA by reducing the effects of GABA. This then releases dopamine release in the nucleus accubens, thus opioids do not act on it directly.

Question 26

What is thought to be the pathway for opioids in the body?

Answer 26

They act in the VTA by reducing the effects of GABA. This then causes dopamine release in the nucleus accubens, thus opioids do not act there.

Question 27

Give 3 counter arguments for the dopamine theory of reward.

Answer 27

1. Addicts often continue taking drugs when they do not feel rewarded/no longer feel pleasure from it
2. Dopamine is only elevated in the nucleus accumbens in reward, but also after unexpected or painful events
3. The dopamine pathways of schizophrenics are damaged (more sensitive to dopamine?) but they are not fat or happy from excessive reward

Question 28

In humans ‘liking’ and ‘wanting’ are separate subcomponents of reward. True or false?

Answer 28

True: liking is a subjective interpretation of ‘niceness’, whereas wanting is a desire for something.

Question 29

The valence of a stimulus is whether it is perceived as positive or negative, essentially its ‘pleasantness’. Activity in which area of the brain is correlated to subjective feelings of pleasantness?

Answer 29

The medial orbitofrontal cortex.

Question 30

The ‘higher’ the reward, the greater the activity in the orbitofrontal cortex. True or false?

Answer 30

True.

Question 31

a) What is another hypothesis for the rise in dopamine activity in the nucleus accumbens?
b) Who came up with this?
c) What evidence is there?

Answer 31

a) Dopamine levels do not rise in response to reward, but in expectation of reward.
b) Wolfe and Schultz
c) When monkeys expected a reward but were not given it, dopamine went up then shot back down.

Question 32

In humans ‘liking’ and ‘wanting’ are separate subcomponents of reward. True or false?

Answer 32

True: liking is a subjective interpretation of ‘niceness’, whereas wanting is a desire for something whether you like it or not.

Question 33

a) What is another hypothesis for the rise in dopamine activity in the nucleus accumbens?
b) Who came up with this?
c) What evidence is there?

Answer 33

a) Dopamine levels do not rise in response to reward, but in expectation of reward. This suggests the VTA-nucleus accumbens pathway is actually involved in reward monitoring/prediction.
b) Wolfe and Schultz
c) When monkeys expected a reward but were not given it, dopamine went up then shot back down.