Conventional Theories of Substance Use and Abuse
The abuse of psychoactive substances is a pattern of maladaptive and self-destructive behavior that, seemingly, offers little or no advantage to the substance user. Traditional explanations (whether they be psychosocial, behavioral, or neurobiological) of substance abuse focus on the pleasurable effects inherent in many psychoactive substances. According to these theories, use of psychoactive substances is rewarded with pleasure, while discontinuation is punished via painful withdrawal symptoms .
The seemingly maladaptive nature of substance abuse makes it difficult for evolutionary theories of human behavior to explain. Despite this difficulty, several theorists have proposed evolutionary explanations for substance abuse, most of which focus (like traditional explanations) on rewards and punishments [2, 3, 4]. In this case, however, rewards and punishments are associated with fitness. Behaviors that encourage survival and reproductive success are rewarded through positive emotions, whereas behaviors that are likely to decrease overall fitness are punished via negative emotions . What psychoactive substances do, in effect, is override the brain's natural reward and punishment centers. The large pleasurable effects of drugs lead the user to believe that drug-use confers fitness advantages; also, these drugs block negative emotional states, preventing the brain from providing accurate information on the decrease in fitness resulting from substance abuse .
This theory is supported by the traditional neurobiological model of addiction which emphasizes the role of the cortico-mesolimbic dopamine system (dopaminergic neurons that project from the ventral tegmental area of the midbrain to the nucleus acumbens of the forebrain) in producing pleasure when a person engages in a fitness-enhancing behavior (eating, sexual activity, etc.) . Psychogenic substances act on the cortico-mesolimbic dopamine system, causing an increase in dopaminergic transmission in the nucleus acumbens and providing pleasure that reinforces the drug use [2,6]. Thus, drugs become associated with fitness advantages, instead of fitness decreases because humans did not evolve in an environment that included frequent exposure to psychoactive substances, and these substances co-opt a natural reward system designed to encourage adaptive behaviors such as eating and engaging in sexual activity.
This view of substance abuse is based on mismatch theory which suggests that human bodies, brains and behaviors evolved over millions of years in an ancestral environment free from modern environmental variables (like widespread and powerful psychoactive substances). Human behaviors, therefore, are adaptive, given an ancestral environment, but as humans encounter modern environments, for which we may be ill-adapted, behaviors can appear maladaptive. There is a mismatch between evolved human behavior and modern environmental demands. Thus drug users, associate drug use with fitness advantages, instead of fitness decreases because humans did not evolve in an environment that included frequent exposure to psychoactive substances, and these substances co-opt a natural reward system designed to encourage adaptive behaviors such as eating and engaging in sexual activity.
Unfortunately, as Sullivan, Hagen, and Hammerstein (2008) note, mismatch theory makes two assumptions which do not appear to be borne out by evidence . One of these assumptions is that psychoactive substances are modern...
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