Reward dependence (RD) is characterized as a tendency to respond markedly to signals of reward, particularly to verbal signals of social approval, social support, and sentiment. When reward dependence levels deviate from normal we see the rise of several personality and addictive disorders.
In psychology, reward dependence is considered a moderately heritable personality trait which is stable throughout our lives. It is an inherited neurophysiological mechanism that drives our perception of our society and the environment. Even though we are born with these personality traits, their expression during our life span can be modulated throughout our development.
Origin and definitions
Reward dependence is one of the temperament dimensions from the "tridimensional personality theory", which was proposed by C. Robert Cloninger as part of his "unified bio-social theory of personality". His personality theory suggested the hypothesis that specific neurochemical transmitters in our brain determine how we respond to a specific stimulus we may experience.
These innate personality traits can play a significant role not only in an individual's predisposition to certain disorders, but also in their maintenance of those disorders.
By understanding the specific temperamental traits that are common among individuals with specific disorders, clinicians can form a more targeted, informed approach to treatment and look to newer psychotherapies for guidance. The relationship between temperament and individual clusters of DSM personality disorders is often investigated. According to the DSM-IV, the tridimensional structure allows up to nine major personality disorders to be identified, the theory thereby making a great contribution to the understanding of psychiatric disorders.
Cloninger's Tridimension Personality Theory and reward dependence
Cloninger's tridimensional personality theory offers three independent "temperament" dimensions which aid in measuring how different individuals feel or behave. Reward Dependence (RD) is one of the three temperament dimensions, the other two being "Harm Avoidance (HA)" and "Novelty Seeking (NS)". A temperament, according to Cloninger, is the automatic emotional response to experience.
Cloninger suggested that RD is influenced by a single monoamine neurotransmitter system: the noradrenergic system and RD is correlated with low basal noradrenergic activity. This suggestion has led to several research experiments that have investigated and supported his hypothesis, that RD traits are indeed in part determined by norepinephrine.
Measure of the RD dimension, as suggested by Cloninger, is used to assess the Altruistic-warm versus detached-tough mindedness components of our personalities.
According to Cloninger's theory, individuals high in reward dependence and low in norepinephrine levels are ambitious, warm, sentimental, pleasant, sociable, sensitive, sympathetic and socially dependent. Individuals with high RD personalities have a disposition to recognize salient social cues which in turn facilitates effective communication, warm social relations, and their genuine care for others, but these individuals are then disadvantaged in being excessively socially dependent. High reward dependent individuals also exhibit persistent behaviors and are easily influenced by emotional appeals.
Individuals low in reward dependence and high in norepinephrine levels are then hypothesized to be typically independent, non-conformist, practical, tough-minded, cynical, unwilling to share their intimate feelings with others, socially detached, irresolute, insensitive to social cues and pressures, and content to be alone. They are also minimally motivated to please others and act for immediate gratification. So being low in reward dependence is related to social withdrawal, with aggressive anti-social behavior, detachment, and coldness in social attitudes.
The RD temperament interacts with other temperaments and characters inherent in us enabling us to adapt to life experiences and influence susceptibility to emotional and behavioral disorders
Quantifying reward dependence
Two questionnaires were devised by Cloninger to measure the temperaments and characters of individuals. RD can be measured using both the Tridimensional Personality Questionnaire (TPQ) personality test and by the newer and refined version of the personality test called Temperament and Character Inventory (TCI) and its revised version (TCI-R). Owing to the limitations encountered in the TPQ, in that the three dimensions' clinical utility was not readily apparent to many clinicians, Cloninger revamped the questionnaire and produced the TCI scale, which incorporates four dimensions of "temperament" and three dimensions of "character".
The so-called subscales of RD in TCI-R are
Sentimentality (RD1) Openness to warm communication or social sensitivity (RD2) Attachment (RD3) Dependence on approval by others (RD4)
A study comparing the TCI to the five factor model of personality found that reward dependence was substantially positively associated with extraversion and to a lesser extent openness to experience.
Brain physiology
Cloninger describes reward dependence as being a prime component of the Behavior maintenance System (BMS). Norepinephrine (NE), apart from producing alertness and arousal, is seen as influencing the brain reward system by aiding in the learning of new paired associations.
According to Cloninger, the norepinephrine neurotransmitter has its major ascending pathways arising in the locus coeruleus in the pons, projecting onward to the hypothalamic and limbic structures, and then branching upwards to the neocortex.
Reward dependence has been linked to "dissociable connectivity streams" in the brain. Striatal projections and Tracts between the prefrontal cortex predict our individual differences in reward processing, reward dependence and reward-guided behaviors. These findings suggest that personality traits may be affected by the strength of limbic-striatal connectivity.
High reward dependence is characterized by learning from reward signals, persisting repetition of actions that are associated with rewards, increased sociability and a need for social approval. The striatum, especially the dorsal regions, is necessary to carry out these functions.
Using Positron Emission Tomography (PET) researchers have shown that reward dependence is linked to opiate receptor binding (the endorphin system) in the bilateral ventral striatum: a core substrate of the reward circuit which is strongly implicated in addictive behavior development. These findings demonstrate that people with high reward dependence (who feel a greater need for social rewards and verbal approval) have more opiate receptors found in the ventral striatum, whereas people with low reward dependence have a lower concentration of receptors. It is then suggested that increased ventral striatal opiate receptors could provide the biological link between personality traits and substance abuse risk.
fMRI studies have shown that individuals with immature development of the inferior part of the frontal lobe around the midline inner surface of the brain, showed greater reward dependence. People with social reward dependence personalities were also seen to have brains with far less tissue in the fronto-striatal section of the brain (e.g. damage to the fronto-striatal area is often linked to autism and schizophrenia). Relationship between concentration of grey matter (brain-cell containing tissue) in different brain regions and social reward dependence was also studied. It was found that the greater the concentration of tissue in the orbitofrontal cortex (the outer strip of the brain just above the eyes), and in the ventral striatum (a deep structure in the centre of the brain), the higher they tended to score on the social RD measure. The researchers warn that these studies are only correlational and cross-sectional and none of this research is definitive in proving that brain structure determines personality but it could be that personality, through experience, may help in determining the structure of the brain. Social Reward Dependence has also been associated with the temporal lobes, the caudate Grey Matter Density (GMD) in the orbitofrontal cortex and the basal ganglia of the ventral striatum. These structures, which are rich in dopamine receptors, are known to play a crucial role in reward receipt, Incentive anticipation and simple and discrete primary and secondary rewards prediction errors. These significant findings show a correlation between primary reward processing circuits and reward dependence, keeping with the fMRI research studies that demonstrated that, following the experience of complex rewards the activation of the striatal circuits occur.
Primary reward processing has also been associated with the orbitofrontal cortex and the grey matter density in the ventral striatum, whereas higher RD scores were associated with the interactions between dopamine projections, neuropeptides and opiates in the ventral striatum. It is demonstrated here, then, that there is evidence for a structural disposition of the brain towards social interactions, and that both sensitivity to salient social reward cues and primary reward processing share the same brain systems.
In addition to these findings, the bilateral temporal poles were also identified in which gray matter density correlated with reward dependence. The medial prefrontal cortex and orbitofrontal cortex, along with other temporal structures, project to the temporal pole, enabling reward stimuli information between the two regions to be integrated. In an fMRI study, the temporal poles and the ventral striatal areas have been shown to be activated in response to social rewards (such as humor) and also in looking forward to simpler rewards (such as money).
Relationship to clinical disorders
Cloninger's theory suggests that over expression of the RD temperament could cause psychiatric illnesses, such as addictive behaviors, sociopathies, and personality disorders.
Low levels of norepinephrine cause an increase in reward dependence. When produced in normal levels, norepinephrine creates a sense of well-being, but low levels of norepinephrine cause symptoms of depression, lack of arousal and lack of motivation. In humans, this leads to then a negative feedback mechanism whereby we seek out pleasurable activities to remove the negative affect caused by the low levels of norepinephrine, therefore increasing our reward dependence.
An increase in the RD temperament leads us to seek out those behaviors or substances that will allow us to remain in a pleasant physical and/or mental state, attributing to the fact that we humans are hedonistic individuals, seeking to avoid pain and embracing pleasurable stimuli. Our pleasure and reward systems in the brain are hyper-activated, which makes us display continuous approach behaviors to the reward in question. Our neuro-circuitry is as such that when we stop having access to such pleasurable objects of desire, we then experience negative consequences (withdrawal symptoms). Addictive behaviors then arise to alleviate such negative consequences and the cycle continues.
Relationship to addictive behaviors
People who have high reward dependent personalities but find themselves in situations where they are unable to find rewards and approval through family support or other types, will seek reward through other means e.g. substance abuse or over-eating. It is then suggested that individuals with such predispositions should adopt preventive strategies or avoid such situations, where they seek such rewards that could potentially have adverse consequences. Reward dependence drives behavior maintenance systems, and in addictive behaviors, maintenance of behaviors occurs despite adverse consequences.