The human brain weighs only 3 pounds, but contains about 100 billion neurons, or nerve cells, which provide the cellular basis for important processes we need to function in everyday life, including our learning, memories, thoughts, feelings, sensations (i.e., sight, taste, smell, touch and sound), movements, motivations and skills. The reward system of the brain is responsible for providing natural rewards and positive reinforcement when we fulfill our biological survival needs for food, water, sex and nurturing. It is human nature to repeat the behaviors that we find pleasurable and rewarding — that is because it is the brain’s reward system’s job to provide rewards that motivate us to do those behaviors that help us survive.
When people abuse drugs or alcohol, they also stimulate the reward system of the brain, which promotes drug-seeking and addictive behavior. Addiction is a primary and chronic disease that changes how important brain chemicals and structures work in the brain. For example, the reward system, which is responsible for rewards, motivation, memory and other processes involved in addiction, plays a major role in behavioral and physiological responses to cues, rewards and cravings in people with alcohol and drug addiction, according to the American Society of Addiction Medicine.
Brain Awareness Week is a global campaign observed during the third week of March that was started in 1996 by the Dana Alliance for Brain Initiatives, a nonprofit organization committed to promoting awareness of the advancements made in brain and neuroscience research. This year, Brain Awareness Week will be observed from March 14-20, 2016. In support of Brain Awareness Week, let’s further explore the role of the brain in addiction.
Neurotransmitters in the brain’s reward system
Alcohol and drugs are chemical substances that can alter the way that neurons send, receive and process information. Drugs of abuse, including alcohol, involve an influx of dopamine in the nucleus accumbens (NA) in the brain’s reward center, which produces the pleasurable feelings or “high” that results from drug or alcohol use. While all drugs of abuse increase dopamine levels in the reward pathway, not all drugs increase dopamine in the same way.
Some drugs contribute to increasing dopamine levels by blocking reuptake through their effect on certain neurotransmitters (i.e., brain chemicals), while others can directly stimulate the release of dopamine. These neurotransmitters, including serotonin, endorphins and GABA, also change the levels of dopamine in the reward pathway. The major neurotransmitters that play a role in drug and alcohol addiction include the following:
Serotonin regulates dopamine release in the NA and plays a role in emotion, appetite, sleep, memory and learning
GABA modulates dopaminergic reward systems and mediates the effects of many drugs of abuse. Certain types of drugs (e.g., benzodiazepines) can inhibit the action of GABA, which disinhibits dopaminergic neurons and makes them fire more rapidly, resulting in reductions in anxiety, behavioral disinhibition, sedation and euphoria.
Endogenous opiates and endorphins (e.g., as in a “runner’s high”) suppress the release of GABA and remove the GABAergic inhibition on dopaminergic neurons in the ventral tegmental area (VTA) and increase dopamine release in the NA, consequently positively reinforcing drug use.
Limbic system: The brain’s reward pathway
The limbic system contains the brain’s reward circuit, which includes structures such as the VTA, NA and substantia nigra, and links together brain structures that control and regulate pleasure in the brain. The limbic system drives important aspects of sexual behavior, motivation and feeding behaviors through its reinforcement pathway in the brain, called the brain’s reward system. The brain’s reward system consists of neurons that release neurotransmitters such as dopamine.
The brain’s reward pathway is primarily made up of structures that are connected by the medial forebrain bundle (MFB) (i.e., the reward circuit or “power line” of the brain’s reward system), a large collection of nerve fibers made up of dopaminergic neurons that travel between the VTA to the hypothalamus and other structures (e.g., amygdala, septum, prefrontal cortex). The MFB becomes activated when a person takes addictive drugs or by other reinforcing and rewarding stimuli (e.g., food, sex), which promotes the release of dopamine in the reward system of the brain.
Several important brain structures are involved in addiction. In particular, the brain’s reward system includes the following structures:
Dopamine release activated by rewards (e.g., food, sex, drugs, etc.) in the VTA increase dopamine levels in the NA.
The amygdala, part of the ventral striatum, is responsible for integrating emotional responses, behaviors and motivation as well as emotionally charged memories, emotional learning and responding to fear-provoking stimuli.
The VTA is one of the principal areas that produces dopamine in the brain.
The hippocampus is part of the limbic system that plays a role in memory function, spatial memory and long-term memory. The hippocampus interacts with the NA by glutamatergic neurons that play a central role in reward.
Specific drugs of abuse can affect neurotransmission in different areas of the brain. The majority of drugs of abuse act on dopamine levels in either the NA or the VTA. The NA is the primary place of action of amphetamine, cocaine, opiates, THC, phencyclidine, ketamine and nicotine, while the VTA is stimulated by opiates, alcohol, barbiturates and benzodiazepines.
Amanda Habermann is a writer for the Sovereign Health Group. A graduate of California Lutheran University, she received her M.S. in clinical psychology with an emphasis in psychiatric rehabilitation. She brings to the team her background in research, testing and assessment, diagnosis and recovery techniques. For more information and other inquiries about this article, contact the author at email@example.com.