In addition to genetics, addiction as a disease is supported by the common signs and symptoms among the homeless and physician drug addicts. The target for drugs of abuse is the brain and changes in the neuroanatomy of the brain occur in all addicts and underlie the disease of addiction. Recent research in neuroscience has identified a specific area of the brain described as the reward center. This area of the brain makes essential survival behaviors such as eating, drinking and sex pleasurable, reinforcing, and thus likely to reoccur. It has become evident that virtually all drugs of abuse target this same area of the brain and result in neurotransmitter brain reward. The problem is that the neurotransmitter changes caused by these drugs far exceed those produced by the natural reinforcers. Animals will press a lever for a drug injection or a puff of cocaine. Once they learn that pressing the lever gives them cocaine, they press and press and press, frequently at the expense of eating, drinking, and ultimately their lives. Unfortunately, the same is true in humans where it is not uncommon to see addicts lose family, careers, and even their lives because of their addiction.
This same area has connections to the emotional areas of the brain (i.e., limbic system). Thus, drug use and addiction can be seen as a disease of brain reward with significant physical and psychological consequences. To truly understand the concept of addiction, one must look at issues of both positive and negative reinforcement. The pleasure effects of the drugs obviously result in positive reinforcement. However, continued drug use ultimately leads to changes in neurotransmitter levels and a host of negative states and emotions (e.g., depression, anxiety, fatigue, etc.). In these cases, continued use of the drug leads to a decrease in these unpleasant effects and results in what is called negative reinforcement (e.g., removal of unpleasant feelings) and the subsequent return to a normal (in this case, drugged brain) state. Research has led to a new understanding of addiction that is not based solely on withdrawal effects.
To understand this process in more detail let us examine the drug cocaine. Drugs like cocaine trick the limbic system by triggering the reward response through the release of neurotransmitters. Neurotransmitters are chemical messengers between nerve cells that are intricately involved in regulating moods. Cocaine use, for example, acutely leads to the increased availability of the neurotransmitter dopamine. Dopamine causes specific nerve cells to fire, and the result is endogenous brain reward or euphoria. Since cocaine uses brain systems normally reserved for species survival reward, the user feels as if he or she has just accomplished something important. The euphoria and brain reward produced by cocaine make the brain view the drug as a substance critical for survival. Hence the brain asks for more cocaine and excessive amounts of dopamine are released. Normally, any surplus dopamine released by the nerve cells is reabsorbed by them; however, cocaine interferes with this reabsorption. Finally, the brain's store of dopamine is depleted. With their supply of neurotransmitters depleted, cocaine users experience intense depression and cravings for more cocaine. In addition, the limbic system remembers cocaine's pleasurable response, a memory that can be triggered by talking about the drug, or smelling it, or even a visual stimulus such as talcum powder. It is believed that the action of drugs in a section of the brain called the nucleus accumbens is primarily responsible for the feelings of positive reinforcement that result from use of virtually all substances of abuse.
Other factors besides the pharmacological effects of drugs may lead to positive reinforcement. For example, drug use may enhance a person's social standing, encourage approval by drug-using friends, and convey a special status to the user. Recent research has shown that environmental factors can account for a considerable amount of the variance attributed to whether teens decide to use or abstain from alcohol (Rose et al.).
Given enough repetitions, drug and alcohol use become as entrenched as the desire for food, water, or sex. Furthermore, the dopamine pathways have many other influences, from the hypothalamus and hormones to the frontal lobe of the brain—the area responsible for judgment and insight. Not only do drugs cause the addict's brain to demand more drugs; the addict's ability to handle this demand rationally in the context of other everyday demands (such as work, family responsibilities, health and safety concerns) is distorted. Tormented by the acquired drive for the drug, memory of euphoria, and denial of obvious consequences, the addict becomes out of control.
Obviously, the complexity of the body and the brain means that no simple answer for the cause of addiction will be found. However, researchers are using sophisticated diagnostic examinations to uncover more information in an attempt to understand better the effects of drugs upon the brain. While it is doubtful that these procedures will provide a definitive, simple answer to the cause of addiction, the information gleaned from them may result in more effective treatment and prevention strategies.
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