Neurophysiology of Reward and Addiction (Pierce) Flashcards
(47 cards)
What is motivation?
A process that mediates goal-directed responses or goal-seeking behavior to changes in the external or internal environment
What is saliency?
Something important in the surrounding env. worth paying attention to; the attention-grabbing feature of rewarding objects.
What does reward involve?
- hedonic effect of pleasure
- motivation to obtain the reward because of its value
- Associated learning
What is aversion?
A negative reinforcement of behavior that the individual will learn to avoid future encounters
What is pleasure?
A subjectively positive sensation
What is the purpose of pleasure?
To promote behaviors that are consistent with survival of self and the species.
What NT plays a role in pleasure reward seeking behavior?
Dopamine
What do DA neurons encode
The discrepancy between reward prediction and information about the actual reward received and broadcast the signal to downstream brain region involved in reward learning.
How do drugs of abuse affect dopamine concentration?
Will increase extracellular concentration of dopamine in limbic regions, including the nucleus accumbens (NA) and prevent reuptake of dopamine
How do drugs increase dopamine and by how much?
- Directly: Inhibiting dopamine reuptake or promoting dopamine release
- Indirectly: Using other neuron receptors that modulate dopamine levels
5-10 fold increase than natural reinforces such as food and sex
What is salience?
A stimuli or environmental changes that are arousing or that elicit an attentional behavioral switch
Why are addicts at a great risk for relapse when they visit places they had taken drugs at?
The stimuli around them are salient (noticeable). The stimuli itself can increase dopamine and elicit desire for drugs.
What are important brain regions in the mesolimbic system
Nucleus Accumbens (NA)
Ventral tegmental area (VTA)
Prefrontal cortex (PFC)
Limbic system
What is the main function of the nucleus accumbens?
Suppress sensations of pleasure and reward
What structures constitutively activate (via EAA like glutamate) nucleus accumbens?
Hippocampus
Amygdala
Prefrontal cortex (PFC)
What type of neurons does the nucleus accumbens release?
GABA (inhibitory)
What is the basic/default circuit of pleasure
- Hippocampus, amygdala & prefrontal cortex release constant trickle of EAA to NA
- NA neurons release GABAergic (inhibitory) neurons to PFC
- Constituitive inhibition of PFC targets keeps the brain in a reward-neutral state (no pleasure)
What pathway occurs when you do something that elicits a reward?
- Dopamine neurons synthesized in VTA project to nucleus accumbens.
- Dopamine released into NA inhibits it.
- NA activity decreases, resulting in a sensation of pleasure
When NA actvity decreases, it can’t inhibit targets in the prefrontal cortex
What stimulates the VTA when you engage in behavior or activity that results in rewards?
Pre-frontal cortex: EAA
Dorsal Tegmental area: ACh
Hypothalamus: Orexin (from food)
What suppresses the VTA to prevent additional release of dopamine and halt the reward process
Projections from the NA back to the VTA which release GABA and a opiod co-transitter called dynorphin
What is the dopamine-hypothesis of reward?
Inactivation of Nucleus Accumbens via dopaminergic neurons from VTA
What is the dopamine-independent reward pathway
Utilizing endogenous opiods to activate the reward pathway
What activities can increase endogenous opioid signaling?
Exercise
Ethanol
Other activities
What receptors do opioid signaling utilize to activate dopaminergic receptors at VTA?
Mu receptors
