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Affective neuroscience lecture 1 (Functions of dopamine (facilitates…
Affective neuroscience lecture 1
Approach motivation and the reward system
Motivation
direction and energisation of behaviour
approach and avoidance
all orgs have approach (reward) and avoidance (threat) capacities
Outputs of reward system
e.g . Desire, hunger, anger, aggression
function
to move organism up a spatiotemporal gradient towards reward
Reward
Aids survival
organism works for
elicits motivation behaviour
a goal
object in space that behaviour is directed towards
Originally thought to be based in nucleus accumbens
target of major branches of dopamine system
Activation and DA release is trigger by sex, drugs of abuse and food
Functions of dopamine
facilitates reward-related processes
behavioural approach
learning, reinforcement
apetite
Implicated in
addiction
parkinson's disease
side effect of dopamine agonstis
dysregulated reward seeking behaviour
MDD
anhedonia
Psychopharmacology
Powel et al
Gave dop agonist to person with anhedonia
saw increased motivation
Molelcular genetics
genetic variation
addictive behaviour
reward seeking in parkinsons
give L-DOPA
genotyped for DRD4 allele, (4 and 7 repeat allele) 7 repeat allele implicated in reward dysregualtion
people with 7 repeat allele when given L-DOPA behave more riskily
Theories of DA reward function
Liking
generation of pleasure
anhedonia hypothesis
DA deficiency explains anhedonia in depression and parkinson's disease
Rats given pimozide (DA antagonist) after being trained to run towards food reward
blocking DA produces effect similar to not getting a reward at all
Problems
not all DA agonists elicit euphoria
rating of euphoria is weakly correlated with dose of DA
hedonic reactions not blunted by DA depletion or enhanced by agonists
seeking/wanting
drive
pre-reward
willingness to expend effort
destroying da producing neurons in rats leads to rats no longer seeking food
subjective craving in humans suppressed by DA blocker
believed that DA mitigates cost of effort to obtain reward
Problems
DA agonists have gradual effect on reward seeking behaviour
learning
formation of association and habits
the stamping in of reinforcement
Phasic activity of DA in VTA
big increase in DA after reward is initially introduced
eventually phasic release of DA shifts back to when conditioned stimulus occurs
reward prediction error
difference between reward prediction and arrival of reward
if reward is greater, RPE is positive
in addition to larger than predicted rewards, DA neurons also respond to aversive stimuli and neutral stimuli
however DA does not code for aversion prediction errors
thought that error related negativity actually due to lack of reward positivity