|• addiction – a state characterized by compulsive engagement in rewarding stimuli, despite adverse consequences|
|• reinforcing stimuli – stimuli that increase the probability of repeating behaviors paired with them|
|• rewarding stimuli – stimuli that the brain interprets as intrinsically positive or as something to be approached|
|• addictive drug – a drug that is both rewarding and reinforcing|
|• addictive behavior – a behavior that is both rewarding and reinforcing|
|• sensitization – an amplified response to a stimulus resulting from repeated exposure to it|
|• drug tolerance – the diminishing effect of a drug resulting from repeated administration at a given dose|
|• drug sensitization or reverse tolerance – the escalating effect of a drug resulting from repeated administration at a given dose|
|• drug dependence – an adaptive state associated with a withdrawal syndrome upon cessation of repeated drug intake|
|• physical dependence – dependence that involves persistent physical–somatic withdrawal symptoms (e.g., fatigue)|
|• psychological dependence – dependence that involves emotional–motivational withdrawal symptoms (e.g., dysphoria and anhedonia)|
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An addictive behavior is a behavior which is both rewarding and reinforcing. It may involve any activity, substance, object, or behavior that becomes the major focus of a person's life resulting in a physical, mental, and/or social withdrawal from their normal day to day obligations.
Typically an individual becomes dependent to a substance to alleviate the pain and agony deriving from certain emotions. The phenomenon occurs subsequent to the first trial where the individual derives some pleasure which increases with additional usage. Continual usage leads to psychological strengthening which ultimately leads to psychological dependence or physical dependence. Drug tolerance is a biological state that occurs when the body adapts to the current amount of the substance. Increased quantities of the desired substance is necessary in order to bring about the same psychologic or physiologic effects previously obtained with smaller dosages, thus it may lead to physical and psychological dependence.
Drug dependence is the term which has formally replaced addiction in medical terminology. In 1964 the World Health Organization Expert Committee on Drug Abuse proposed that the terms addiction and habituation be replaced with the term dependence and distinguished between two types psychological dependence and physical dependence.
From the 1920s to the 1960s attempts were made to differentiate between addiction; and habituation, a less severe form of psychological adaptation. In the 1960s the World Health Organization recommended that both terms be abandoned in favor of dependence, which can exist in various degrees of severity. Addiction is not a diagnostic term in ICD-10, but continues to be very widely employed by professionals and the general public alike.
Dependence and addiction
Psychological dependence vs addiction
Although psychological dependence and addiction are often used interchangeably by laypersons and clinicians, the two terms correctly refer to distinct concepts that arise through different mechanisms. Addiction involves pathological positive reinforcement (reinforcement associated with reward) and is associated with intense cravings or compulsions involving a rewarding stimulus (addictive drugs, sex, etc). Psychological dependence involves pathological negative reinforcement and is associated with continued drug use so as to avoid an unpleasant emotional-motivational withdrawal syndrome.
Compulsion vs addiction
Compulsions and addictions are intertwined and reward is one major distinction between an addiction and a compulsion (as it is experienced in obsessive-compulsive disorder). An addiction is, by definition, a form of compulsion, and both addictions and compulsions involve reinforcement learning; however, in addiction, the desire to use a substance or engage in a behavior is based on the expectation that it will be rewarding (i.e., involves positive reinforcement). In contrast, someone who experiences a compulsion as part of obsessive-compulsive disorder may not get any reward from the behavior he carries out. Often, it is a way of dealing with the obsessive part of the disorder, resulting in a feeling of relief (i.e., also includes negative reinforcement).
It is interesting to note that Deep brain stimulation to the Nucleus Accumbens, a region in the brain involved heavily in addiction and reinforcement learning, has proven an effective treatment of obsessive compulsive disorder.  This indicates that addictions and Obsessive Compulsive Disorder may share components of their neural basis.
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