Reward, motivation and addiction . relative to the basal ganglia. :
ventral tegmental area (VTA);
nucleus accumbens (NAc);
prefrontal cortex (PFC);
amygdala (AMY);
hippocampus (HIPP). "; both work on the
dopamine system. Cocaine seems to hijack the
reward system by artificially overstimulating dopamine neurons. Addiction involves a phenomenon known as
incentive salience, also called "wanting" (in quotes). Incentive salience differs from craving in that craving is a
conscious experience while incentive salience may or may not be. While incentive salience can give feelings of strong urgency to cravings, it can also motivate behavior
unconsciously, as in an experiment where
cocaine users were unaware of their own decisions to choose a low dose of cocaine (which they believed was
placebo) more often than an actual placebo. Brain scans of people in love using
fMRI (commonly while looking at a
photograph of their beloved) show activations in these areas like the VTA and NAc. The dorsal striatum is implicated in reinforcement learning, Academics have proposed a number of theories for how addictions begin and perpetuate. One prominent theory developed by
Wolfram Schultz involves a dopamine signal which encodes a
reward prediction error (RPE): the difference between the
predicted value of a reward, which would be received by performing a particular action, and the
actual value upon receiving it: whether the reward was better, equal to or worse than expected. An alternative model developed by
Kent Berridge and
Terry Robinson states that dopamine signaling causes the motivational output (incentive salience) which is proportional to RPE, but that the dopamine signal itself may be an effect of learning rather than causing it directly. One study has investigated whether people in long-term romantic relationships experienced RPE in response to having expectations about their partners' appraisal of them validated or violated, indicating they do. This study used fMRI to find that reward areas like the VTA and striatum responded in a way consistent with other research on RPE. Most fMRI studies of romantic love have had participants look at a photograph, and the resulting reward system activity has been interpreted in terms of salience. Academics do not universally agree on whether or not love is always an addiction or when it needs to be treated. The term "
love addiction" has had an amorphous definition over the years and does not yet denote a
psychiatric condition, but recently one definition has been developed that "Individuals addicted to love tend to experience negative moods and affects when away from their partners and have the strong urge and craving to see their partner as a way of coping with stressful situations." Other authors include rejected lovers as love addicts, or specify that love is an addiction when it involves abnormal processes which carry negative consequences. A broader view is that all love is addiction, or simply an
appetite, similar to how humans are dependent on
food. Romantic love may be a "natural" addiction, which differs from the nature of drug addiction in that love may be prosocial and has been evolved for the purpose of pair bonding. Additionally, the hypothalamus projects oxytocin to other areas of the brain, like the
ventral tegmental area (VTA),
nucleus accumbens (NAc),
amygdala, and
hippocampus. The projections to reward areas (VTA and NAc) are thought to modulate
social salience, or i.e. the level of
dopamine activity in response to socially-relevant stimuli. The role of oxytocin in human behavior is varied and complex. Oxytocin can be released with physical
touch, hence it's also sometimes called the "cuddle hormone". but this research is also used for making inferences about humans. While opioids have their origin being the body's natural
painkiller, they're also implicated in a variety of other systems, essentially like
neurotransmitters. Opioid receptors are located throughout the brain, including in the
limbic system (affecting basic
emotions) and
neocortex (affecting more
conscious decision-making). Opioids are linked to the consummatory part of reward, or i.e. "liking" or pleasure, and released in areas of the brain called
hedonic hotspots (or pleasure centers). Hedonic hotspots are located in the
nucleus accumbens, the
ventral pallidum and other areas. Other animal studies have shown that endogenous opioids play a role in the desire for
rough-and-tumble play (a physical, but also social behavior). An
fMRI experiment in 2010 investigated whether viewing a picture of a romantic partner could reduce pain sensitivity, and which areas of the brain became active. Participants were exposed to high temperatures (resulting in moderate or high pain levels) while viewing a picture of a romantic partner (whom they were intensely in love with), or a friend, or performing a
word association task which has also been shown to reduce pain via
distraction. Participants were then asked to rate how much pain they felt on a
pain scale, and both viewing a romantic partner and performing the distraction task (but not viewing a friend) were found to reduce pain levels. The fMRI scans revealed that viewing a romantic partner activated
reward circuits in the brain, while the distraction task did not. Brain areas were also correlated with pain relief to reveal that reward analgesia and distraction analgesia involved distinct areas. Some areas associated with
sensory processing of pain also had decreased activity while viewing a romantic partner. Other modern studies on humans include
blood plasma levels,
genetics and studies with drugs like
morphine and
naltrexone to see how they change social perception and behavior. The thoughts also differ in function and content. Some reports have been made that people can even spend as much as 85 to 100% of their days and nights thinking about a love object. One study found that on average people in love spent 65% of their waking hours thinking about their beloved. A 2025 study led by Adam Bode also found no association between
SSRI use and obsessive thinking about a loved one, or the intensity of romantic love. Therefore, although the earlier experiments do suggest romantic love and serotonin are probably associated, the authors suggest that the idea of obsessive thinking being attributed to lowered serotonin levels seems inaccurate.
Emotional valence Rather than being a specific
emotion itself, romantic love is believed to be a
motivation or drive which elicits different emotions depending on the situation: positive feelings when things go well, and negative feelings when awry. Reciprocated love may elicit feelings of
joy,
ecstasy, or
fulfillment, for example, but
unrequited love may elicit feelings of
sadness,
anxiety, or
despair. A 2014 study of Iranian young adults found that the early stage of romantic love was associated with the brighter side of
hypomania (elation, mental and physical activity, and positive social interaction) and better
sleep quality, but also stronger symptoms of
depression and anxiety. Those authors conclude that romantic love is "not entirely a joyful and happy period of life". Romantic love may be either pleasant or unpleasant, regardless of the intensity level. The intensity of love feelings is also distinct from whether an individual is satisfied with their relationship (although the measures have been shown to be related to some extent). One can be satisfied with their relationship because it fulfills some other need besides love for their partner (like
money or
child care), or conversely be in love with an abuser in an
abusive relationship. A different study found 63% had a "huge crush" at least once in the past 2 years (but not letting the person know), and unrequited love was four times more frequent than equal love. In 2010, Helen Fisher, Arthur Aron and colleagues published their
fMRI experiment investigating which areas of the brain might be active in recently rejected lovers. Participants had been in a relationship with their
ex-partner for an average of 21 months, and then were post-rejection for an average of 63 days at the time of the experiment. Similar to other fMRI experiments, the scan while looking at a photograph of the rejecting partner showed activations in
dopaminergic reward system areas, like the
ventral tegmental area and
nucleus accumbens. These activations were also stronger than in a previous experiment of participants who were happily in love. The active nucleus accumbens,
prefrontal cortex, and
orbitofrontal cortex have been associated with assessing one's gains and losses, and active areas of the
insular cortex and
anterior cingulate cortex have been involved with
physical pain and pain regulation (respectively) in other studies. Some experiments have been done which support the idea that the stress response is involved during the early stage of romantic love, measuring
cortisol levels; however, these experiments have been inconsistent with respect to cortisol being higher or lower. Helen Fisher believed that separation anxiety activates the HPA axis, producing these
stress hormones. It's ironic, she says, because short-term stress can also produce
dopamine and
norepinephrine, so "as the adored one slips away, the very chemicals that contribute to feelings of romance grow even more potent".
Frustration attraction and uncertainty Dopamine neurons in the
ventral tegmental area are theorized to encode a "reward prediction error" (RPE) signal, rather than a reward per se. This RPE signaling indicates whether a given reward was either better, equal to, or worse than what was anticipated, and this is believed to be part of a
reinforcement learning paradigm. The phenomenon has been remarked on by many authors, such as
Socrates,
Ovid, the
Kama Sutra, and "
Dear Abby".
Bertrand Russell once opined that "when a man has no difficulty in obtaining a woman, his feeling toward her does not take the form of romantic love". Some common social barriers are parents who interfere with their children's romance (as in
Romeo and Juliet), deceived spouses, or other social customs. A comparable type of situation is that of a
slot machine, where the rewards are designed to be always unpredictable so the
gambler cannot understand the pattern. Unable to
habituate to the experience, for some people the exhilarating high from the unexpected wins leads to
gambling addiction and
compulsions. If the machine paid out on a regular interval (so that the rewards were expected), it would not be as exciting. Uncertainty theory in the context of romantic love is associated with
Dorothy Tennov's theory of
limerence, an addictive, infatuated kind of love, commonly experienced for an unobtainable or unreachable person. According to
Elaine Hatfield, 'Consistency generates little emotion; it is inconsistency that we respond to. If a person always treats us with love and respect, we start to take that person for granted. We like him or her—but "ho hum." [...] What would generate a spark of interest, however, is if our admiring friend suddenly started treating us with contempt—or if our arch enemy started inundating us with kindness.' or seeing through rose-colored glasses. In the past, some authors have depicted the phenomenon as a malady, arguing that people who idealize would have their partner fall short of their high expectations as a relationship progresses; however, despite this, significant modern scientific evidence has shown that positive illusions actually contribute to relationship satisfaction, long-term well-being and decreased risk for relationship discontinuation. The exact mechanism is not currently understood, but some brain areas are proposed to be related. The
dopaminergic areas of the
reward system which are active in romantic love may be involved with attributing
salience to the positive characteristics of a loved one. The
dorsal anterior cingulate cortex is involved with error detection and has been active during negative social evaluation and exclusion, so that reduced activation of this area would be an adaptive response to a partner's negative characteristics. Certain areas of the
prefrontal cortex could also be exerting top-down control to suppress emotional responses to attractive alternatives. Information is then passed to the
orbitofrontal cortex, where positive and negative information is weighed, resulting in a biased subjective value about the partner. == Brain imaging ==