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.