Reward Dependence and Reward Deficiency

Abstract

In this chapter, we outline the neural network involved with reward value. We emphasize the prominent role of dopamine (DA) within the mesocorticolimbic system of the network in mediating the reinforcing effects of drugs. The cascade of neuronal events leading to the net release of DA at the nucleus accumbens is detailed, followed by a discussion of the evolutionary genetics of dopamine and the dopamine D2 receptor gene. Based on the scientific support sampled, we posit a common underlying mechanism of action for the powerful effects that all addictions have on human motivation. That is, biological drives may have common molecular genetic antecedents, which, if impaired, lead to aberrant behaviors. We further hypothesize that 'reward genes,' especially dopaminergic genes and other candidate neurotransmitter-related gene polymorphisms, affect both hedonic and anhedonic behavioral outcomes. Reward genes are important common determinants of a generalized set of behaviors as a phenotype. We refer to this phenotype as Reward Deficiency Syndrome (RDS). RDS refers to the breakdown of a cascade of neurotransmitters in the brain in which one reaction triggers another—the reward cascade—and resultant deviant conduct. RDS is a genetic phenotype; it does not represent any one single addictive behavior. Genetic association studies have amassed strong evidence implicating the DRD2 gene in harmful conditions such as alcoholism. Additionally, the dopamine D2 receptor gene (DRD2) has been found to be involved in other substance use disorders including cocaine, nicotine, and opioid dependence, as well as obesity, poor impulse control, sex addiction, gambling, Internet gaming, and certain neuropsychiatric conditions. We hypothesize that there is a common neurochemical mechanism of action for the powerful effects that food, sex, and acquired addictive precursors have on human motivation; all have common molecular genetic antecedents that if impaired lead to aberrant behaviors. In discussing RDS, we refer specifically to an insensitivity and inefficiency in the brain's reward system. RDS also encompasses acquired needs to escape or avoid painful states or negative feelings. Impairment in the mechanisms involved in these processes can lead to multiple impulsive, compulsive, and addictive behaviors. Applications and clinical relevance are discussed with reference to reward deficiency disorders and substance abuse treatment. (PsycInfo Database Record (c) 2022 APA, all rights reserved)