Reward Deficiency Syndrome. The Reward Deficiency Syndrome (RDS) results from a dysfunction of the dopaminergic reward system of the brain. The RDS was firstly referred to in research of addictive behaviours – and particularly in studies of alcoholism (Xxxx, Xxxx, Xxxxxxxxx, & Xxxxxxx, 1996; Xxxx & Xxxxx, 1990). The RDS originated from the association between alcoholism and the dopamine receptor gene DRD2 (Xxxx et al., 1996). Dopamine is an important neurotransmitter in the brain’s reward system and is known to control moods and feelings of well-being (Xxxxxxx, 2007). Individuals who suffer from underactivation (i.e. a deficiency) of the dopaminergic system, often due to genetic predispositions, will engage in activities that increase the activation of the system in order to receive the pleasant stimulation of its activation (Comings & Xxxx, 2000). Whereas the RDS originated from genetics, it has now come to refer to a dysfunctional state of the reward system independent of any specific genetics (Xxxx, Cull, et al., 1996; Xxxx & Xxxxx, 1990; Xxxxxx, et al., 2011). Several reward- related disorders, such as addictions and ADHD, are characterised by deficient activation of brain regions in response to rewards and are thus referred to as reward deficiency disorders (Xxxx, Xxxx, et al., 1996). In fact, the RDS has been suggested to explain a number of reward seeking behaviour such as extreme impulsivity and novelty seeking, which are often manifested in the form of antisocial behaviours (Comings & Xxxx, 2000). The reward deficiency hypothesis may help explain increased risk taking in adolescence as well as reward-related disorders such as ADHD (see Table 1 and Table 2). The impulsivity hypothesis is an opposing theory of the RDS hypothesis. It suggests that a combination of excessive reward seeking and failure of effective inhibition underlies novelty seeking and impulsive behaviour. Whereas the RDS hypothesis suggests that novelty seeking and impulsivity are the result of an underactive reward system, the impulsivity hypothesis suggests that these behaviours result from an overactive reward system in combination with insufficient inhibitory control (Ernst, Xxxx, & Xxxxxx, 2006; Xxxxxx, Xxxxx, & Xxxxxx, 2011). The impulsivity hypothesis was initially based on the fact that longitudinal studies suggested that individuals who demonstrated poor behavioural self-control or high novelty seeking in childhood were substantially more likely to initiate substance use and other reward seeking beha...
