Riley Dopamine 1 Flashcards
What is learning?
Associations, representations and predictions about future rewards based on past experiences (Berridge & Kringelbach, 2008)
What is the law of effect?
According to Thorndike (1898) selection of behaviour is determined by Law of Effect.
Responses leading to pleasant stimuli tend to occur more often; those leading to unpleasant stimuli occur less often
What makes a stimulus rewarding?
If an animal will work for it. It’s an action of the mind, whether it is perceived as rewarding
What is positive reinforcement?
Action that leads to the presence of positive stimulus
What is negative reinforcement?
Action that leads to the removal of negative stimulus
What is punishment?
If pressing a lever leads to negative stimulus then they’re less likely to press it
How can rewarding stimuli be explained in evolutionary terms?
Almost all rewarding stimuli can be explained in evolutionary terms e.g. food, sex, socialisation
What animals can we see the conditioned response in?
Can see it in zebra fish, rats, crocodiles and pigeons
Can generalise findings across species as there must be some evolutionary preserved models
Can we justify animal models?
It allows for the use of a broader range of experimental techniques that may not be ethical in humans
They are too invasive to be ethical in humans e.g. deep brain recordings, brain stimulation
What is the issue with fMRI in these studies?
fMRI doesn’t actually show where a neural event occurs and can show other things instead
Doesn’t have great spatial resolution
What is the issue with EEG in these studies?
Only on surface level and can’t get to the relevant deep brain regions
What is optogenetics and how is it relevant?
Can insert specific genes and send LED light into the brain. There are then specific neurons that only fire when light of a specific wavelength is applied
This means this technique has a high degree of control
Where does the ventral tegmental area (VTA) project to?
Axons can project to distant regions
The VTA projects to the Nucleus Accumbens (NAc) which is one of the main reward regions
This projection causes dopamine release in the NAc
Why are rats often used in research?
The reward circuitry is preserved from rats to humans
What are the three neurotransmitters involved in the human reward model?
- Glutamate
- GABA
- Dopamine
What are the Glutamate projections in the human reward model?
The PFC (involved in higher cortical processing), Hippocampus (involved in memory) and the Basolateral Amygdala (involved in drive and motivation) project to the NAc
What are the GABA projections in the human reward model?
The NAc projects to the VTA (involved in reward prediction)
The ventral pallidium (involved in motor response) projects to the NAc, with the NAc also projecting to the ventral pallidium
What are the Dopamine projections in the human reward model?
VTA projects to the NAc
What is the difference in fish?
Fish don’t have a NAc but have a subpallium which is thought to fulfil this role
What did Olds and Milner show?
In 1954 they showed that the brain has specialised centres for reward functions
Implanted rats with deep brain stimulating electrodes
Rats placed in Skinner box, whenever they entered a specific corner the NAc was electrically stimulated
Rat would repeatedly return to areas where they would experience the NAc stimulation
What has been found in animals and NAc stimulation?
That they will favour lever pressing stimulating the NAc over almost any other stimuli e.g. food, sex
They will even run over an electric grid to get to the NAc stimulation
How can the reward value be modulated by drugs of abuse?
Amphetamine increases the reward value of stimuli
Pimozide (DA antagonist) reduces the reward value of stimuli
What implications does this have for depression research?
There is the potential to explore NAc stimulation as an option for pharmacologically resistant depression
But should surgical treatments be a last resort?
