7. Physiology of Reward & Addiction Flashcards
what is motivation
changes in the external or internal environment mediate goal-directed responses or goal-seeking behavior
what is reinforcement
- operant (learned) behaviors that change the probability that a behavior will be repeated under similar conditions each time
what is saliency
something important in the surrounding environment worth paying attention to
Salience = stimuli or environmental changes that are arousing or that elicit an attentional-behavioral switch
–> affects motivation to seek anticipated reward & facilitates conditioned learning.
==> associated with drugs that increase DA –> elicit the desire for drug (reason why pt is at risk of relapsing)
what is a reward
Objects, stimuli, or activities w/ positive value
what is aversion
a negative reinforcement of behavior –> individual learns to avoid future encounters
what is the basis of pleasure
= positive sensation
AKA euphoria or hedonia
purpose= promote behaviors consistent with survival of self and the species
what encodes discrepancy btn reward prediction & actual reward
DA neurons send signal to downstream brain regions involving reward
- unpredicted reward - activation
- predicted reward- no respone
what is the basis for preference of drug use
Over repeated drug use–> repetition of reward prediction error (RPE) signals
–> reinforce drug-related cues and behaviors ==> contrast to natural rewards (which produce error-correcting DA-RPE signals only until the predictions match the actual events)
so–> given the choice between drug and natural reward develops a bias towards drug that strengthens with each drug use.
what hormone NT is affected by drugs of use
- DA
- increased [DA] extracell in limbic regions ( like nucleus accumbens)
- longer and large increase in DA
(some increase directly & others indirect)
what are the components of the mesolimbic system
nucleus Accumbens (NA)
ventral tegmental area (VTA)
the limbic system
pre-frontal cortex (PFC).
(uses DA)
what is the basic circuit
PFC/amygdala/hippo activate NA w/ Glu –> supress sensation of pleasure/reward
–> release GABA and inhibit PFC
–> keep brain in reward-neutral state (no pleasure)
what is the reward circuit
DA neurons from VTA to NA
–> inhibit NA –> decrease NA activity -
-> results in sensation of pleasure
= DA-hypothesis of reward
(DA-independ reward path - activate reward path)
how is VTA activated
behavior/activity that causes reward –> VTA activated by EAA, orexin or ACh
[PFC- EAA
dorsal tegmental area: Ach
hypothal: orexin (consumption of food)]
- exercise, ethanol –> activate endogenous opoids –> bind mu receptors –>
- activate VTA DA neurons by inhibiting local interneurons that supress DA activity
- activate local interneurons of NA (inhibit local neurons)
- activate PFC
what is the reward feedback circuit
NA back to VTA
–> inhibit via GABA & dynorphin (cotransmitter)
–> bind kappa-opiod receptors -
CREB –> supress DA release form VTA
what is dynorphin
an opoid
binds kappa opiod receptor in VTA
