da 4

Question 1

What is Schultz theory (1998)

Answer 1

midbrain dopamine release represents a reward error. - the differece between received and predicted rewards. no learng when reward is entirely predicted.

Question 2

Schults (1997) monkey

Answer 2

recorded extracellular activity from midbrain DA neurons while monkeys performed behavioural tasks.

• press lever to get juice after light is on
• dopamine neuron is activated by unpredicted occurence of reward before learning
• after learning: conditioned stimulus causes increase in dopamine after reward no increase.
• if no reward given : decrease in dopamine following when reward should have been.

Question 3

what is a raster plot

Answer 3

represents firing of neurons in time. Horizontl rows = single trial.

Question 4

what is a reward prediction error?

Answer 4

the reward prediction error acts as a teaching signal that is used to correct inaccurate predictions.

Dopamine response = reward occurred- reward predicted.

Question 5

RPE and blocking

Answer 5

blocking *Cs1 fully predicts stimulus so CS2 not conditioned,

Blocked stimuli- doesnt become associated with reward- no reward= no change, reward = increase in da

unblocked stimuli- reward does become associated.
reward- no change
no reward= reduction in da firing

Question 6

Enomoto et al., (2011)

Answer 6

stepwise transfer of DA to the earliest predicting stimuli

Question 7

RPE and risk taking

Answer 7

Stauffer et al., 2014
monkeyy cued to make a reward based decision: 50;50 chance of getting a juice reward. or garanteed small reward.
** when risk high:
High midbrain activity associated with cue
reduced midbrain activity at time of reward.

Question 8

problem with RPE response.

Answer 8

the timing of the DA response too slow

BUT Riorillo et al., 2013: midbrain response comprises of 2 phases:
an unselective transient phase that cues any potentially salient object
second phase codes for reward value of a stimulus.

Question 9

Does da release at nac represent rpe ?

Answer 9

Hart et al., 2014: ast scan cyclic votammetry- displays bidirectional rpe signal.

Question 10

implication for rpe processing in the nac

Answer 10

conditioned responses

Coincident cortical NAc synaptic activity with VTA DA strengthens conditioned responses.
da release is required for corticostriatal plasticity (lerner and kreitzer, 2011)
positive rpe- higher concentration of da released = liklihood of potentiation.

Question 11

implication 2

Answer 11

The nac projects to the basal ganglia to initiate motor selection. positive RPE the strongest bid is put in to the BG.

Question 12

Summary

Answer 12

• The firing of midbrain dopaminergic neurons represents a reward prediction error.
• if an action produces an unpredicted positive outcome, it is likely to be repeated: positive RPE - increase in DA firing
• if an action produces an unpredicted negative outcome, it is likley to be repeated: negative RPE= decreased da firing
  no further learning takes place when a reward is entirely predicated by sensory cues.