Reward And Addiction Flashcards
What is motivation?
A process that mediates goal directed responses or goal seeking behavior to changes in the external or internal environment
What is reinforcement?
The consequences of operant (learned) behaviors that alters the probability that a behavior will be repeated under similar conditions each time
What is salience?
Something important in the surrounding environment worth paying attention to
The attention grabbing feature of rewarding objects (think of it as wanting)
Describe salience
Heightens perception and focuses attention toward the particular sights, sounds and smells associated with these rewards in a way that normally promotes well being and survival
Typically triggered by encounters with reward related cues and experienced as surges of motivation to obtain and consume the reward that can last beyond the time the individual is exposed to the cue
Something having salience = something has value to the individual so that they want it
What is reward?
Involves hedonic effect of pleasure, motivation to obtain the reward because of its value (salience) and associated learning
What is aversion?
A negative reinforcement of behavior that the individual will learn to avoid in future encounters
What is pleasure/hedonia?
A subjectively positive sensations often referred to as euphoria or hedonia
Think of it as liking
What is anhedonia?
Lack of interest in something (no longer liking something you used to)
What is the physiologic purpose of pleasure?
To promote behaviors that are consistent with survival of self and the species
What is reward prediction error (RPE)?
Mismatch between events and reward elicited
An unpredicted reward elicits an activation (positive prediction error)
A fully predicted reward elicits no response
Omission of a predicted reward induces a depression (negative prediction error)
Dopaminergic neurons encode the discrepancy between what?
Reward predictions and information about the actual reward received and broadcast this signal to downstream brain signals involved in reward learning
Describe drugs of abuse
Increase extracellular dopamine concentrations in limbic regions including the NA
Drugs of abuse provide longer and large increases in dopamine than natural reinforcers like food and sex
Some drugs increase dopamine directly (ex. Cocaine, amphetamine, meth and ecstasy)
Other drugs work indirectly via other neuron receptors that modulate dopamine levels (ex. Nicotine, alcohol, opiates and marijuana)
What are the important brain regions for reward and addiction?
The mesolimbic system such as NA, ventral tegmental area (VTA), prefrontal cortex (PFC), limbic system
What is the main function of the nucleus accumbens (NA)?
To suppress sensations of pleasure/reward
Describe the nucleus accumbens
Is constitutively activated by a constant trickle of EAA like glutamate from the hippocampus, amygdala, or even the PFC
NA neurons are GABAergic meaning that activation of these neurons stimulate them to release GABA upon their target and inhibit it
Inhibit the PFC which keeps the brain in a reward neutral state (no pleasure)
What is the reward circuit?
When you do something that elicits a reward the VTA becomes activated which inhibits the NA
- DA neurons from the VTA project to the NA
- DA is released into the NA and inhibits its neurons
- NA activity decreases
- Decreased NA activity results in sensation of pleasure
What is the VTA activated by?
Upon engaging in a behavior or activity that results in reward the VTA is activated by EAA, orexin or ACh
These NTs may arise from the PFC (EAA), other tegmental nuclei like the dorsal tegmental area (ACh) or in the case of consumption of food from the hypothalamus (orexin)
What is the reward feedback circuit?
There exist projections from the NA back to the VTA and in this case GABAergic neurons from the NA project back into the VTA where they inhibit it
In addition to releasing GABA the NA neurons also release a co-transmitter called dynorphin (an opioid that binds to kappa-opioid receptor in the VTA)
Together the GABA and dynorphin function to suppress additional release of dopamine from the VTA as a means to halt the reward process
What is the dopamine hypothesis of reward?
Together the inactivation of the NA via dopaminergic neurons from the VTA is termed the dopamine hypothesis of reward
Many drugs of abuse activate the mesolimbic DA system and the associated hedonic effect is a result
What is the dopamine independent reward pathway?
Also activates the reward pathway
Exercise, ethanol and other activities increase endogenous opioid signaling at all levels of the reward network including the VTA, NA and PFC
How do exercise, ethanol and other activities elicit the dopamine independent reward pathway?
Via activation of mu receptors they activate
1. DA neurons in the VTA via inhibiting local VTA interneurons that would normally suppress DA activity therefore opioids disinhibition DA neurons
2. Local interneurons in the NA which inhibit the GABAergic neurons locally
3. The PFC itself
The net result is a profound sense of pleasure or even euphoria
Describe normal reward stimuli
Due to release of dopamine from VTA
Purpose is to reinforce behaviors consistent with health, longevity and otherwise done seem to have an immediate benefit
The reward for these behaviors is the sense of pleasure that is derived
Describe rewards due to drugs of abuse
Manny drugs enhance dopamine release from VTA
Dopamine signal in the NA is not proportional to stimuli
The reward for this is enhanced euphoria and exaggerated reward to an otherwise mild stimulus
What role does the hippocampus have?
A lasting memory is crated that associates rewarding feelings with the circumstance and environment in which they occur called conditioned associations
