Substance Use Disorders: Assessment and Treatment, 2nd Edition _ ___________________________________
Although these dynamics have been known for many years, it is only since the 1970s, with the development of new tools allowing for the study of actual neurobehavior, that researchers have been able to focus on and identify the impact of differ- ent substances on both brain structures and their functions. Although much of the increased understanding of the neuro- biology of addiction is beyond the scope of clinicians working to help individuals who are abusing substances, some basic knowledge is essential to provide practitioners with greater insight into the processes of addiction and recovery. The brain is a complex organ with multiple structures. How- ever, three specific areas—the limbic system, the prefrontal cor- tex, and the hypothalamic-pituitary-adrenal (HPA) axis—have been implicated in SUDs. Moreover, the important roles of neurons and numerous neurotransmitters in SUDs have only recently been recognized and are still being identified (Logrip et al., 2011). Three parts of the limbic system (Figure 1) play a critical role in SUDs: the amygdala, the hippocampus, and the reward circuit: 1. The amygdala regulates basic drives,
NEUROBIOLOGY OF ALCOHOL AND OTHER DRUGS The addiction potential of different substances varies greatly; for example, narcotics or crack cocaine have a much higher addiction potential than alcohol or marijuana. In general, the more rapid the onset of the drug’s effects and the shorter the period of time the effects last, the more reinforcing the drug will be (Muller, 2020)—meaning that the drug is likely to pro- voke consistent use more often over a shorter period of time, leading to brain changes and greater risk of dependence. The route of administration of a drug is also relevant with respect to the dangers of developing dependence. For example, inhaling a drug gets a larger amount of the drug to the brain faster than injecting the drug, and injecting a drug gets a larger amount of the drug to the brain faster than ingesting it. Moreover, the impact of the different substances on the brain leads to such dynamics as tolerance, withdrawal symptoms, craving, relapse , and a variety of other physiological reactions that clinicians working with individuals with substance use disorders (SUDs) need to understand. Various concepts related to the neurobiology of addiction will be discussed in this chapter. Addiction to alcohol and other drugs is based on three factors: tolerance, psychological dependence, and physical dependence. Tolerance is a term that describes an individual’s need, over time, for more and more of the substance to achieve the desired effect (the “high”). Tolerance is an indicator of the body’s changing chemistry in response to the frequency and quantity of use. Psychological dependence is a term used to describe the individual substance user’s feelings or beliefs that he or she needs more and more of a drug to function normally, whether or not this is actually the case. The term physical dependence is used when a person must continue to use the drug in increas- ing quantities to function normally. A person who decreases or stops use will experience withdrawal symptoms that can typically be alleviated or controlled by taking the same or a chemically similar drug. A drug that has a high potential for all three of these factors—tolerance, psychological dependence, and physical dependence—in combination with some other known and unknown factors, such as genetics, is said to have high addictive potential (NIDA, 2021a).
emotions, and attentiveness; it coordinates both stress and drug reward systems and is central to survival, signaling a person’s “fight or flight” response in the event of a perceived threat to safety. It is responsible for autonomic reactions implicated in stress responses, such as accelerated heart rate and respiration, and it links emotional responses with the muscle responses responsible for action (Gothard, 2020). The amygdala is also responsible for determining which experiences related to pain and pleasure will be encoded into memory. The hippocampus is thought to mediate all memories, including those related to traumatic events and learned responses to cues. These processes have key implications for triggering relapse caused by memories of intensely pleasurable experiences related to past drug or alcohol use, as well as those related to stress or traumatic reactions. The reward circuit begins in the ventral tegmental area, then moves forward into the nucleus accumbens, and finally into the prefrontal cortex. It generates a sense of pleasure and desire for specific experiences. It is designed to reward a person for doing those things that increase the likelihood of survival and reproduction: eating when hungry, drinking when thirsty, participating in nurturing social behavior, and having sex. Because these are very basic biological needs, the reward circuit is a very powerful driver of behavior. The reward circuit significantly
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Self-Assessment Question
1. What is tolerance?
A) The individual substance user’s feelings or beliefs that he or she needs more and more of a drug to function normally B) When a person must continue to use the drug in increasing quantities to function normally C) An individual’s need, over time, for more and more of the substance to achieve the desired effect (the “high”) D) All of the above
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