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Addiction is a state characterized by compulsive engagement in rewarding stimuli, despite adverse consequences. It can be thought of as a disease or biological process leading to such behaviors.〔 The two properties that characterize all addictive stimuli are that they are reinforcing (i.e., they increase the likelihood that a person will seek repeated exposure to them) and intrinsically rewarding (i.e., something perceived as being positive or desirable).〔〔〔 Addiction is a disorder of the brain's reward system which arises through transcriptional and epigenetic mechanisms and occurs over time from chronically high levels of exposure to an addictive stimulus (e.g., morphine, cocaine, sexual intercourse, gambling, etc.).〔〔〔 ΔFosB, a gene transcription factor, is a critical component and common factor in the development of virtually all forms of behavioral and drug addictions;〔〔〔〔 two decades of research into ΔFosB's role in addiction have demonstrated that addiction arises, and addictive behavior intensifies or attenuates, along with the genetic overexpression of ΔFosB in the D1-type medium spiny neurons of the nucleus accumbens;〔〔〔〔 due to the causal relationship between ΔFosB expression and addictions, it is used preclinically as an addiction biomarker.〔 ΔFosB expression in these neurons directly and positively regulates drug self-administration and reward sensitization through positive reinforcement, while decreasing sensitivity to aversion.〔〔 Addiction exacts an astoundingly high toll on individuals and society as a whole through the direct adverse effects of drugs, associated healthcare costs, long-term complications (e.g., lung cancer with smoking tobacco, liver cirrhosis with drinking alcohol, or meth mouth from intravenous methamphetamine), the functional consequences of altered neural plasticity in the brain, and the consequent loss of productivity. Classic hallmarks of addiction include impaired control over substances or behavior, preoccupation with substance or behavior, and continued use despite consequences. Habits and patterns associated with addiction are typically characterized by immediate gratification (short-term reward), coupled with delayed deleterious effects (long-term costs). Examples of drug and behavioral addictions include: alcoholism, amphetamine addiction, cocaine addiction, nicotine addiction, opiate addiction, exercise addiction, food addiction, gambling addiction, and sexual addiction. The only behavioral addiction recognized by the DSM-5 is gambling addiction. The term ''addiction'' is misused frequently to refer to other compulsive behaviors or disorders, particularly ''dependence'', in news media. ==Behavioral addiction== (詳細はcompulsion to engage in a natural reward – which is a behavior that is inherently rewarding (i.e., desirable or appealing) – despite adverse consequences.〔〔 Preclinical evidence has demonstrated that that overexpression of ΔFosB through repetitive and excessive performance of a natural reward induces the same behavioral effects and neuroplasticity as occurs in a drug addiction.〔〔〔 Reviews of both clinical research in humans and preclinical studies involving ΔFosB have identified compulsive sexual activity – specifically, any form of sexual intercourse – as an addiction (i.e., sexual addiction); moreover, reward cross-sensitization between amphetamine and sexual activity, a property in which exposure to one increases in the desire for both, has been shown to occur preclinically and clinically as a dopamine dysregulation syndrome;〔〔〔 ΔFosB expression is required for this cross-sensitization effect and it intensifies with the level of ΔFosB expression as well.〔〔 Reviews of preclinical studies indicate that long-term frequent and excessive consumption of high fat or sugar foods can produce an addiction (food addiction or sugar addiction).〔〔 Exercise appears to be associated with an addictive state (exercise addiction),〔 but there is also significant preclinical and some clinical evidence that it prevents and can treat drug addictions, particularly those involving psychostimulants.〔 Gambling is a natural reward which is associated with compulsive behavior and for which clinical diagnostic manuals, namely the DSM-5, have identified diagnostic criteria for an "addiction";〔 however, no research has been conducted to determine if the overexpression of ΔFosB (the 35–37 kD isoforms) is present in deceased gambling addicts to confirm that the DSM's diagnostic model correctly diagnoses an addiction instead of a compulsion. There is evidence from functional neuroimaging that gambling activates the reward system and the group of neurons where increases in ΔFosB gene expression occur in an addiction, the mesolimbic pathway.〔 Similarly, shopping and playing videogames are associated with compulsive behaviors in humans and have also been shown to activate the reward system and the mesolimbic pathway in particular.〔 Based upon this evidence, gambling addiction, video game addiction and shopping addiction are classified accordingly.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「addiction」の詳細全文を読む スポンサード リンク
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