Substances and the Brain
Areas of the brain that are impacted by substances of abuse: Substances can alter important brain areas that are necessary for life-sustaining functions and can drive the compulsive use of substances that marks addiction. Brain areas that are affected by substance use include: 1.) The brain stem, which controls basic functions critical to life, such as heart rate, breathing, and sleeping. 2.) The cerebral cortex, which is divided into areas that control how information is processed from person's senses, such as the ability to see, feel, hear, and taste as well as areas that power a person's ability to think, plan, solve problems, and make decisions. 3.) The limbic system contains the brain’s reward circuit. It links together a number of brain structures that allow a person feel pleasure. Feeling pleasure motivates a person to repeat behaviors that are critical to sustaining life. It is activated by healthy, life-sustaining activities such as eating and socializing, but it is also activated by substances of abuse.
How substances of abuse work in the brain: Drugs are chemicals that affect the brain by interfering with its communication system and changing the way brain cells (neurons) normally send, receive, and process information. Some substances, such as marijuana and heroin, can activate brain cells because their chemical structure mimics that of a natural chemical messenger (neurotransmitter). This similarity in structure tricks the brain and allows the drug to attach onto and activate the brain cells. Although these drugs mimic the brain’s own chemicals, they do not activate brain cells in the same way as a natural chemical messenger. This leads to abnormal messages being sent and received. Other substances, such as amphetamine or cocaine, can cause the brain cells to release abnormally large amounts of natural chemical messengers or prevent these brain chemicals from cycling normally. Most substances of abuse directly or indirectly target the brain’s reward system by flooding the circuit with dopamine, which is a type of chemical messenger, or neurotransmitter. Dopamine is present in parts of the brain that regulate movement, emotion, motivation, and feelings of pleasure. When activated at normal levels, this system rewards natural behaviors such as eating or sex. Over stimulating the system with drugs, however, produces euphoric effects, which strongly reinforces the behavior of drug use, teaching the user to repeat it.
Why a person continues to use substances: A person's brain is wired to ensure that life-sustaining activities will be repeated by associating those activities with pleasure or reward. Whenever this reward circuit is activated, the brain notes that something important is happening that needs to be remembered. It teaches a person to repeat the behavior without thinking about it. Substances of abuse stimulate the same area of the brain; therefore a person learns to use the substance in the same way. When some substances of abuse are used, an excess of 2 to 10 times the amount of dopamine is released compared to the amount released by natural rewards. To put this into perspective, the difference between normal rewards and drug rewards can be described as the difference between someone whispering and someone shouting into a microphone. The brain is then forced to adjust to the overwhelming surge in dopamine by producing less. This adjustment causes the reward center to function at a decreased capacity, which decreases that person's ability to experience any pleasure. Individuals that use over an extended period of time report feeling unhappy, flat, lifeless, and depressed. In order to feel any pleasure, they must try to bring their dopamine level up. Substance users do this by increasing their intake of the substance (tolerance). This is a vicious cycle. In the end, an individual cannot feel pleasure when they “get high,” and they cannot feel pleasure when they are not “high.”
Long-term effect of substance use: Researchers have proven that the same mechanisms involved in the development of tolerance can eventually lead to profound changes in the function of the brain. This has the potential to severely compromise the health of the brain and may cause cognitive impairment. Long-term use of substances can also trigger adaptations in the development of habits or non-conscious memory systems. For example, over time, a person's daily routine or environment becomes associated with substance use and can trigger uncontrollable cravings even when the drug itself is not present. This can result in relapse even in individuals who have sustained long periods of abstinence.
Medical consequences of substance use: People who suffer from substance use disorders often have one or more accompanying medical issues, which may include lung or cardiovascular disease, stroke, cancer, HIV/AIDS and Hepatitis B and C. Imaging scans, chest X-rays, and blood tests show that substance use causes damaging effects throughout the body.
Mental health and substance use: Substance use disorder and mental health conditions often co-exist. In some cases, diagnosis such as anxiety, depression, or schizophrenia may precede addiction; in other cases, substance use may trigger or exacerbate these diagnoses, particularly in people with specific vulnerabilities.
* Continue on to the next section to learn about specific substance use disorders.