Lecture 5 reward Flashcards
What are the different types of primary rewards/reinforcers?
Taste Odour Somatosensory Visual Auditory Other
What are some taste rewards?
Salt
Sweet
Unami
What are some odour rewards?
Pheromones
Of food
What are some somatosensory rewards?
Gentle touch/ grooming
Warm temperature
Washing / bathing
What are some visual rewards?
youthfulness/ beauty
Facial expression
“nature”
What are some auditory rewards?
soothing vocalisations/ music
What are some other rewards?
Attachment Sexual behaviour exercise Play Novelty seeking
How is reward expressed?
Through pleasure centres
What research is there on pleasure centres
- Olds & Milner 1954 discovered
- Electrode stimulation technique: found that rats would ‘work’ for stimulation of specific midbrain sites and felt they had found part of brain for reward.
What makes up the basal ganglia?
Caudate nucleus, putamen and striatum
What is the ventral tegmental area?
Dopamine expressing neurons
What is the substantia nigra pars compacta?
dopamine expressing neurons
What does the nucleus accumbens do?
Receives dopamine from VTA
What did Heath argue about dopamine?
That dopamine was the happiness drug, and that people would self reward like rats and would crave pleasure and rewarding stimulus more
What challenges are there to the dopamine reward hypothesis?
- If you lesion dopamine reward areas leads to loss of learning but not loss of pleasure
- drugs of abuse that target dopamine lead to craving without pleasure
- Heath mis-reported data
What are some possible hedonic hotspots?
- Shell of nucleus accumbens (ventral striatum)
- Ventral Pallidum
- Parabrachial nucleus in brainstem
- orbitofrontal cortex?
- Insula?
What does the orbitofrontal cortex do?
Reward value and decision making
What research looks at reward and value?
Critchley and Rolls (1996)
- Gave drops of blackcurrent on the tongue
- Presented smells of either blackcurrent, apple or banana or non edible
- Cell only active for edible stimulus
- As they get more and more black they don;t want it, so activity in the cell decreases for black but also for apple and banana
How is dopamine involved in reward and error prediction in animals?
Monkeys associate light and reward
- before association get baseline firing and spike when they get reward, this is error because they are not expecting reward
- once association learned, get a spike after the light has come on, showing prediction
- On catch trials, they get a dip of activity because they are predicting a reward but they don’t get it.
What research has been done into dopamine reward and error in humans?
Similar to animals but using monetary reward,
More firing if they are not expecting a reward and less firing if they are expecting reward.
How do dopamine neurons learn to predict?
Hebbian learning strengthens the association between cortical inputs and inputs from the striatum to dopamine neurons if reward is present.
What happens if two neurons fire together?
They wire together
What is the primary motor cortex always doing?
Planning different actions
What does the striatum do?
Plans which actions will go ahead
All information about sensory context will go here
A sort of cross-benefit analysis
How does reward driven activation work?
The motor cortex plans actions and sends them to the thalamus, if the thalamus fires, the motor cortex neurons will fire.
The striatum then decides which action should go ahead.
What are D1 neurons part of?
The direct pathway- go pathway
They have receptors that make them more likely to fire when there is more dopamine around.
What are D2 neurons part of?
The indirect pathway- no go pathway
They have receptors that make them more likely to fire when there is less dopamine around.
What are the neurons in the striatum?
Spiny projection neurons which are inhibitory (GABA) neurons that have a low baseline firing rate
What are the two types of dorsal striatum firing neurons?
D1 & D2
How does the direct pathway work?
D1 neurons connect to the substantia nigra pars reticulata, neurons here are inhibitory but are tonically active (active all the time) these are permanently inhibiting the thalamus.
When D1 started firing they inhibit the neurons they are connected to, so substantia nigra pars reticulata neurons stop inhibiting, meaning they stop inhibiting neurons in the thalamus, so thalamus neurons fire and the signal for the movement to take place happens.
How does the indirect pathway work?
D2 neurons are inhibitory and inhibit the globus pallidus external capsule- which has tonically active neurons when these are inhibited, they stop firing and connect to the substantia nigra pars reticulata which then inhibits the thalamus
How is it decided which pathway wins?
The substantia nigra pars compacta - if you found action rewarding before then dopamine neurons here start to fire and these are connected to the striatum. If there is more dopamine then the D1 neurons will fire, if there is not much dopamine the D2 neurons will fire.
