Reinforcement and the striatum Flashcards
Define a drive.
An innate, biologically determined urge to achieve a goal or satisfy a need.
Define reinforcement.
The process of strengthening an organisms future behaviour.
What drives reinforcement?
Reward: stimuli that increase the probability of particular behaviour.
Define an appetitive reinforcement.
The reward is a positive stimulus, e.g. food.
Define aversive reinforcement.
The reward is a negative stimulus, e.g. pain.
What are the reward/reinforcement areas in the brain thought to be?
The ventral striatum, particularly the nucleus accumbens.
The ventral striatum is part of the basal ganglia complex. This is composed of 5 individual nuclei in primates. What are they?
- Striatum
- External segment of globus pallidus (GPe)
- Internal segment of globus pallidus (GPi)
- Subthalamic nucleus (STN)
- Substantia nigra (SN)
There are 2 midbrain dopamine pathways. What are they?
- The mesolimbic pathway
2. The mesocortical pathway
What structures are included in the mesolimbic pathway?
The VTA, the amygdala, the hippocampus and the nucleus accumbens (there are others but I won’t remember them).
What are disorders in the mesolimbic pathway associated with?
Faulty reward and reinforcement behaviour.
What structures are included in the mesocortical pathway?
The VTA, prefrontal cortex and hippocampus (there are others but I won’t remember them).
What are disorders of the mesocortical pathway associated with?
Schizophrenia.
What happens in the nucleus accumbens when the VTA is stimulated by an electrode?
Dopamine levels increase.
What happens in the nucleus accumbens when a subject is presented with food?
Dopamine levels increase.
What happens in the nucleus accumbens during sex?
Dopamine levels almost double in rats.
Do nicotine and cannabis cause elevated dopamine levels in the nucleus accumbens?
Yes.
What is the point of self-administration experiments?
To see whether the subject likes a drug and look at which brain areas are stimulated during drug use.
What effect do cocaine and amphetamine have on dopamine levels in the nucleus accumbens?
Increased dopamine levels.
What effect did using a dopamine blocker have in self-administration experiments?
The rat kept administering more and more drug, trying to achieve the sense of reward afforded by dopamine release.
What happened in self-administration experiments of cocaine when the animal had lesions to the nucleus accumbens?
The self-administration was greatly reduced. The nucleus accumbens could not properly release dopamine so no ‘reward’ was felt.
What do heroin and morphine act on within the body?
Endogenous opioid receptors.
What is the natural function of endogenous opioids?
To supress pain, a survival technique.
Injecting opiates has what affect on dopamine in the nucleus accumbens?
Increased levels.
What happens to self administration of opioids if there are lesions to the nucleus accumbens?
Self-administration does NOT reduce, suggesting there must be a different pathway for opioid action.
What is thought to be the pathway for opioids in the body?
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.
What is thought to be the pathway for opioids in the body?
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.
Give 3 counter arguments for the dopamine theory of reward.
- Addicts often continue taking drugs when they do not feel rewarded/no longer feel pleasure from it
- Dopamine is only elevated in the nucleus accumbens in reward, but also after unexpected or painful events
- The dopamine pathways of schizophrenics are damaged (more sensitive to dopamine?) but they are not fat or happy from excessive reward
In humans ‘liking’ and ‘wanting’ are separate subcomponents of reward. True or false?
True: liking is a subjective interpretation of ‘niceness’, whereas wanting is a desire for something.
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?
The medial orbitofrontal cortex.
The ‘higher’ the reward, the greater the activity in the orbitofrontal cortex. True or false?
True.
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?
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.
In humans ‘liking’ and ‘wanting’ are separate subcomponents of reward. True or false?
True: liking is a subjective interpretation of ‘niceness’, whereas wanting is a desire for something whether you like it or not.
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?
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.
