Lecture 25: Reward Flashcards
What has the study of addictive hedonic drugs revealed?
much about the brain mechanisms of reward and motivation
Which sites in the brain produce huge self-stimulation responses?
a path from the ventral medial forebrain to the rostral brainstem, centred around a fibre tract called the median forebrain bundle
What is the dopaminergic pathway involved in addictive behaviour?
dopamine neurons of the ventral tegmental area which project to the nucleus accumbens
What is the ventral tegmental area (via the median forebrain bundle) a source of?
dopamine to prefrontal cortex and associated basal ganglia regions
What is the mode of action of some hedonic drugs (such as opiates)?
facilitate dopamine release by VTA neurons on frontal regions
What are some dopaminergic agonists (e.g. amphetamines) powerful elevators of?
mood
What does dopamine from the VTA + synaptic potentiation result in?
greater inhibition of ventral pallidum
less inhibition of MD thalamus
greater excitation of limbic cortex
What is dopamine released in proportion to?
the accuracy to which reward is predicted
What is the role of dopamine?
increases the association between cortical inputs and the accumbens
What does the prefrontal cortex encode?
values, goals, and how behaviour should be structured
What is the accumbens co-activated by?
motivation-state inputs e.g. amygdala, cingulate, brainstem?
What happens if some behaviour / cortical activity leads to reward?
something makes the VTA release dopamine (because of the
activity predicted reward) which strengthens that cortex-accumbens association
Where are most of the nuclei that dopamine is involved in (diffuse modulatory systems)?
in the “central core” of the brain: the brainstem and basal forebrain
What are characteristics of diffuse modulatory systems of the central nervous system?
a nucleus or cluster of nuclei with relatively few neurons (thousands rather than millions)
highly divergent
the synapses made by these cells are typically “en passant”
What do reports from self-stimulating humans suggest?
a mental state other than reward (perhaps anticipation of a potential rewarding state)
What may addictive behaviour relate to?
reward or the anticipatory state, but seems to be dopaminergic
What is significant about taste, liking and disliking behaviours?
are conserved and involve regions of ventral striatum
What do rats depleted of striatal dopamine exhibit?
do not seek food, but exhibit liking and disliking behaviours for palatable (sugar) and unpalatable (quinine) food
What happens in regards to the activity of VTA neurons when there is no conditioned stimulus and a rat is given a reward?
activity of VTA dopamine neurons increases upon receiving the reward
What happens in regards to the activity of VTA neurons when there is a conditioned stimulus and a rat is given a reward?
activity of VTA dopamine neurons increases upon noticing the conditioned stimulus but there is no increase in activity upon receiving the reward
What happens in regards to the activity of VTA neurons when there is a conditioned stimulus and a rat is not given a reward?
activity of VTA dopamine neurons increases upon noticing the conditioned stimulus but there is a decrease in activity upon realising that it will not receive the reward
What is the definition of dopamine in neuroeconomics?
the amount of dopamine released is about how much reward you thought you were going to get vs. how much you did get
