REWARD & PLEASURE Flashcards
“Liking” is the pleasure component (hedonic impact) of reward, including:
– Core pleasure reaction that is not necessarily conscious
– Conscious experience of pleasure
“Wanting” is the motivational component of reward, including:
– Incentive salience that is not necessarily conscious
– Conscious desires for incentives or goals
“Learning” is the associative and predictive component of reward, including:
– Associative conditioning, such as Pavlovian and operant associations
– Cognitive predictions
Intensity:
– How loud a sound is
– How strong a taste or smell is…
Valence:
– Subjective value of outcome
– Positive valence is pleasantness
– Negative valence is unpleasantness
Intensity and valence interact:
– Asymmetrically correlated between valences
e.g., negatively-valenced stimuli can be more intense than positively-valenced stimuli
– Correlated within valence
e.g., more intense smell can be more negatively valenced
Brain areas contributing to reward and pleasure
Ventral pallidum
Nucleus accumbens (in ventral striatum)
Orbitofrontal cortex
Amygdala
Thalamus (for instance, mediodorsal nucleus)
Midbrain (includes ventral tegmental area)
Orbitofrontal cortex (OFC) involved in adaptive decision-making
Valence represented differently in different regions of OFC
– Functional MRI shows different BOLD activity in different OFC regions depending on valence
Mid-anterior OFC (orange) faithfully represents sensory pleasures
– Including sensory rewards such as taste
Medial OFC (green) involved in learning and memory of rewards
– Also responds to pleasant stimuli
Lateral OFC (purple) helps monitor disincentives and negative reinforcers
– Responds to unpleasant stimuli
Anterior OFC represents complex or abstract reinforcers, e.g., money
– Posterior OFC represents less complex reinforcers
Specific satiety signaling in orbitofrontal cortex of monkeys
Response of orbitofrontal neurons decreased during consumption to satiety
– E.g., response to glucose decreased to near zero
This satiety effect was specific to the substance consumed to satiety
– E.g., although response to glucose decreased, there was little change in response to blackcurrant
This satiety effect was not due to peripheral adaptation
– No corresponding decrease in response from, e.g., nucleus of solitary tract in brainstem
Orbitofrontal cortex (OFC) involved in adaptive decision-making
OFC encodes valence:
– This valuation needed for selecting goals
– Seek out high-reward items and avoid aversive items
OFC maintains representations of expected rewards:
– Informs about consequences following particular actions
OFC learns and updates reward expectations:
– Based on reward prediction errors, e.g., signaled by dopaminergic midbrain neurons
OFC predicts future reward based on abstract rules or problem structure:
– E.g., probabilistic reversal learning (involves flexible stimulus-reward associations)
OFC contributes to computation of decisions:
– At the very least, the consequences of decisions
Endogenous opioid system
Endogenous opioids
– endorphins
– enkephalins
– dynorphins
Brain uses opioids for:
– analgesia (i.e., pain relief)
– reward (re: food and drugs)…
Pleasure involves opioids in:
– nucleus accumbens
– ventral pallidum
“Hedonic hotspot” in nucleus accumbens for pleasure generation
Effect of opioid agonist microinjections
– orange/red: increased hedonic reactions
– purple: reduced aversive reactions
– blue: reduced hedonic & aversive reactions
– green: increased motivation to eat (but no change in reactions)
Nucleus accumbens (NAc) sites contributing to desire and dread
Inhibiting NAc produced
intense motivations
– e.g., injected GABA agonist
– increased eating (desire) or
– increased fearful reactions (dread)
e.g., escape attempts, distress calls, defensive actions, etc
Likely mechanism of action:
– disinhibited downstream areas
– e.g., ventral pallidum
Cortex to nucleus accumbens to ventral pallidum to thalamus to cortex
disinhibitory circuit involving nucleus accumbens and ventral pallidum like “direct pathway” involving striatum and internal segment of globus pallidus
Hedonic hotspot” in ventral pallidum
Effect of opioid agonist microinjections
– red: increased hedonic reactions
– blue: reduced hedonic reactions
Effect of GABA blockade (increasing pallidal activity)
– red: increased wanting and eating
Ventral tegmental area contributes to learning and reward prediction
Cells in ventral tegmental area (VTA) signal reward prediction errors:
– increased activity for unexpected reward
– little change in activity for expected reward
– reduced activity for withheld reward
VTA cells release dopamine at their targets:
– orbitofrontal cortex
– nucleus accumbens
– ventral pallidum
Electrical self-stimulation of the ventral tegmental area (VTA)
Electrodes implanted in VTA or along its projection to forebrain
– particular behavior leads to stimulation
– e.g., lever press
Sometimes rats continued electrical self-stimulation until exhausted
– Not interested in food or water
Dopamine release in the forebrain reinforced lever pressing
– Stimulating VTA cells or their axons caused
dopamine release at their targets
Recent evidence suggests dopamine increased wanting, without pleasure?
– Dopamine also involved in reward prediction
Addictive drugs increase effect of dopamine in nucleus accumbens
Heroin and nicotine increase dopamine release in nucleus accumbens
– heroin and nicotine respectively act at opiate and cholinergic receptors on dopaminergic neurons in VTA
Cocaine prolongs dopamine action at dopamine receptors in nucleus accumbens
– cocaine blocks re-uptake of dopamine by dopamine transporter
Amygdala plays a role in computing stimulus values
Neurons in amygdala encode stimulus value in appetitive and aversive tasks
– This includes information about stimulus intensity
– Negative (aversive) coding may contribute to fear conditioning
Amygdala provides information about stimulus values to orbitofrontal cortex
– Uncinate fasciculus (red, below) connects amygdala and orbitofrontal cortex
Many pleasures: one hedonic brain system for them all?
Different pleasures feel different
– Food
– Sex
– Drugs
– Social, e.g., seeing friend or family member
– Cognitive, e.g., listening to music
But different pleasures tend to activate similar brain areas
– Orbitofrontal cortex (as well as other cortical areas, i.e., anterior cingulate, insula)
– Nucleus accumbens
– Ventral pallidum
– Amygdala
– Midbrain
Possibly this key network of brain areas provides “pleasurable gloss” to all rewards
– Even when the final experience of different rewards feels different
