10. Neurophysiology of Reward and Addiction Flashcards
Define motivation
process that mediates goal-directed responses or coal-seeking behaviour to changes in the external or internal environment
Define Saliency
something important in the surrounding environment worth paying attention to
Define reinforcement
consequence of operant behaviours that alters the probability that a behaviour will be repeated under similar conditions each time
Define Reward
objects, stimuli or actiivities that have positive valie
Define aversion
a negative reinformement of behaviour that the individual will learn to avoid future encounters
Define pleasure
a positive sensation often referred to as euphoria or hedonia
promotes survival of self and others
Describe how dopamine and drug use go together? (longest FC ever)
- dopaminergic neurons encode the discrepancy between reward predictions and info about the actual reward received and send this signal to the reward learning centers of the brain
- unpredicted reward elicits an activation (positive prediction error; a happy suprise)
- a fully predicted reward elicits no response (exactly what you thought would happen)
- Omission of a predicted reward induces a depression (sad that you didn’t get what you thought you would)
- events that always precede reward assigns value to the reward itself
- with repeated drug use, repetition of these reward prediction error signals reinforces drug related cues and behaviours
- natural rewards (not drug related) produce error-correcting DA-RPE signals only until the predictions match reality
- as a result, when given a choice between drugs or natural reward, there is a bias towarsd the drug that strenghtens with each use
Drugs reinforce drug use via dopamine. How so?
drugs can increase extracellular dopamine concentrations in the limbic region and nucleus accumbens and last longer and are in larger amounts than other natural reinforcers like food and sex
cocaine, meth, and ecstasy increase dopamine directly by inhibiting dopamine reuptake or promoting dopamine release
ETOH, nicotine, opiates and MJ work indirectly to increase dopamine levels
What causes a drug abuser to seek out more drugs, especially in certain environments?
Salience allows certain enviromental sensory cues associated with the drug can increase dopamine levels and elicit the desire for more drug
Salience also contributes to drug induced dopamine increases leading to the procurement of more drug
What keeps us from feeling pleasure all the time ?
GABAnergic neurons release GABA from the nucleus accumbens to the prefrontal cortex
this inhibits pleasure
How do we overcome the inhibition by the Nucleus Accumbens to feel pleasure based on pleasurable stimuli?
AKA dopamine-hypothesis of reward
when a reward is elicited, the ventral tegmental area becomes activated to inhibit the nucleus accumbens in five steps
- dopaminergic neurons from the VTA project to the NA
- DA is released into the NA
- DA inhibits neurons in the NA
- NA activity decreases
- decreased NA activity allows for pleasure to be sensed
What type of rewards activate the ventral tegmental area?
Excitatory amino acids (prefrontal cortex)
orexin (hypothalamus after eating)
Ach (dorsal tegemental area)
How is the ventral tegmental area inhibited to stop the pleasure sensation?
GABAnergic neurons from the nucleus accubnes release GABA back onto the ventral tegemtnal area
also releases dynorphin as a co-transmitter which binds to kappa-opiod receptors and supresses further dopamine release from the VTA
What is the dopamine-independent reward pathway?
the ventral tegmental area can aslo be activated by opioids (endogenous via exercise, ethanol, etc)
Via activation of mu receptirs, they activate dompinaergic neurons in the VTA, activate local interneurons in the NA, and activate the PFC causing pleasure/euphoria
What are some major outcomes of chronic drug exposure in the brain?
it alters the morphology of neurons in the dopamine regulated circuit
it can alter the expression of transcriotion factors and prorteins
it can change the level of NTMs in the brain, leading to more compulsive and disinhibited behaviour
