task 4 Flashcards
dopamine
Dopamine comes from the VTA and NA (nucleus accumbens). Dopamine from the VTA is connected to primary rewards, while the NA dopaminergic neurons are more responsive to secondary rewards such as money. Dopamine projects to the VS and (in addiction) to the DLS.
Olds and Milner identified brain regions in rats that activated in response to reinforcement / self-stimulation
the medial forebrain bundle (MFB) induced the highest rates of self-stimulation. It is connected to dopamine cells in the VTA. Additionally, activity in the MFB was found to be related to fluctuations in dopamine levels in the nucleus accumbens.
reward-prediction error hypothesis of dopamine
Whenever there is a reward-prediction-error, dopaminergic neurons will respond (=reward-prediction error hypothesis of dopamine)
(three-factor learning rule
the same dendritic spines of MSNs are contacted by both glutamatergic input from the cortex (coding aspects of the environment) and dopaminergic input from the midbrain (signaling that adjustments are necessary). Synaptic transmission is strengthened on the neurons that receive both inputs.
Contingent feedback allows dopaminergic projections to modify behavior in response to salient stimuli
One mechanisms why phasic dopamine could support learning is suggested by the observation that long-term potentiation (LTP) in the striatum depends not only on strong pre- and postsynaptic activation, but also on dopamine release
Dopaminergic midbrain neurons respond at 2 timepoints during learning:
- In response to the reward predicting stimuli
o In proportion to the subjective value of the reward predicted by the stimuli - In response to the receipt or omission of the expected reward
o In proportion to the difference between expected and received reward
The VS is active at both timepoints, with stronger activation at the second. The SN and the VTA also show reward-related activity.
primar vs secondary
The VS is activated by primary rewards during both classical and instrumental conditioning. The foci in the NA are however more densely clustered when it comes to monetary rewards, causing a stringer and more robust response to monetary rewards. This indicates that the NA is more involved in the processing of secondary rewards, while the VS especially activated in response to surprising rewards and in settings that require learning to maximize rewards
wllhuhn
- Projections from the VTA to the VMS (ventromedial striatum) are central to drug reinforcement, because the concentration of dopamine in the VMS is increased when a drug is used.
- The elevated dopamine is maintained by regulating the rate of responding (taking the drug).
- The stimuli (CS) that are repeatedly paired with the drug also become able to elicit changes in dopamine concentration.
- These phasic responses last only a few seconds but still control drug seeking and taking.
willhuhn finings
- Drug cue-induced phasic dopamine release in the VMS is present early in cocaine self-administration and continues but decreases .
The CS presentation alone (even when not followed by cocaine) was sufficient to elicit a VMS dopamine signal while the motor response of poking did not. - Phasic dopamine signaling in the DLS develops over weeks / the course of drug taking. The dynamics in the DLS therefore follow an opposite direction than those from the VMS. Responses in the DLS start to increase when those in the VMS decrease.
- Dopamine receptors in the DLA are necessary for discriminated responses to obtain cocaine.
- Development of phasic dopamine signaling in the DLS depends in the VMS
Three-factor learning rule
Three-factor learning rule: the same dendritic spines of MSNs are contacted by both glutamatergic input from the cortex (coding aspects of the environment) and dopaminergic input from the midbrain (signaling that adjustments are necessary). Synaptic transmission is strengthened on the neurons that receive both inputs.
Contingent feedback allows dopaminergic projections to modify behavior in response to salient stimuli
Ventral striatal activation in reward learning
Dopaminergic midbrain neurons respond at 2 timepoints during learning:
- In response to the reward predicting stimuli
o In proportion to the subjective value of the reward predicted by the stimuli
- In response to the receipt or omission of the expected reward
o In proportion to the difference between expected and received reward
The VS is active at both timepoints, with stronger activation at the second. The SN and the VTA also show reward-related activity.
From primary to secondary reinforcers
the NA is more involved in the processing of secondary rewards, while the VS especially activated in response to surprising rewards and in settings that require learning to maximize rewards.
cognitive feedback
Cognitive feedback about the correctness of an answer is another kind of reinforcer, especially considering that it is some kind of social approval (conditioned reinforcer). While monetary rewards give extrinsic motivation (which weaken intrinsic motivations), cognitive feedback induces intrinsic motivation / rewards
In a study where the participants either received information about the correctness of their answer of money for every correct answer, the NA was activated more strongly in response to cues predicting monetary reward compared to those predicting feedback (see figure A).
Reward related processing in the ventral striatum is dependent on the motivational states induced by the type of rewards (intrinsic or extrinsic).
be careful VS
Activity in the VS does not always indicate the value of a reinforcer, since the VS has been found to also respond to non-rewarding events with negative outcomes
the VS responds to errors in reward prediction rather than to the errors themselves.
vs and confidence
In other studies, the VS was additionally found to be associated to confidence: activity increased when the participant was more confident than expected and decreased when less confident than expected (figure B). thus, even in the absence of external feedback, activity in the VS tracks confidence in decisions, which is inherently related to the ability to successfully navigate the task environment to obtain potential rewards.
The global signaling scheme
As drug use progresses, several processes engage in it (incorporation of sensoritomor DLS (dorsolateral striatum) in the control of established / habitual drug seeking behavior / CS-elicited reward seeking).
The global signaling scheme assumes that reward-associated cues produce transient increases in the firing rate of dopamine neurons throughout midbrain nuclei (encompass entire striatum). This uniform phasic dopamine signaling has been challenged by the notion that dopamine release in response to natural rewards takes place in the VMS but not in the DLS
