Physiologic Effects

So what happens in the brain of people when they take a drug into their body? A simple review of basic brain anatomy and physiology will assist in understanding substance abuse and addiction. Although a comprehensive review of this topic is beyond the scope of this course, a list of resources is provided for those interested in further study of this aspect of addiction.

The organized layers of the brain can be thought of like floors in the house. Vital functions such as heart rate, breathing, and blood pressure are controlled by the brain stem, hind-brain, and mid-brain--the first floor.8

The central core of the brain--the second floor--is divided into two sections: the hypothalamus and the limbic system. The hypothalamus controls important biological functions such as sex drive, thirst, hunger, sleep cycle, energy level, the immune system, and "pleasure centers." The limbic system is called the "emotional brain" and plays an important role in regulating emotional behavior.8

The cortex, the third floor, is the highest level of the brain and is responsible for perception, information processing, thinking, reasoning, and higher cognitive functions. The frontal lobes of the cortex can be thought of as the penthouse. The front halves of these lobes are especially critical because they are active in inhibiting emotional reactions, maintaining attention and concentration, and enabling complex thinking and problem solving.8

The inside in the brain at the molecular level can be compared to the wooden structure of the house in that wood is made up of millions of grains. The grain in the wood is like the millions of nerve cells (neurons) that make up the brain. Normal brain function is dependent on the appropriate action of neurons. Each neuron functions by producing and releasing a particular chemical substance called a neurotransmitter. These neurotransmitters are called messenger molecules because they influence other neurons and assist in the transmission of messages from neuron to neuron. Neurotransmitters can impact the function of the nerve cell by activating and inactivating the cell and causing adjacent cells to produce and release hormones or to grow or to die.8

The neurotransmitters that have been associated with addiction include serotonin, dopamine, norepinephrine, gamma-amino-butyric acid (GABA), and glutamate. Medications, recreational drugs such as alcohol and cocaine, stress, genetic factors, and hormonal factors have been found to interfere with nerve cell function. This discussion will focus on the interaction between alcohol, drugs, neurotransmitters, the brain's pleasure center, and addiction.8

The pleasure centers of the brain are areas that are part of an internal biological reward system. They are activated by the release of particular neurotransmitters that are triggered by certain life experiences. Under normal circumstances, experiences such as watching a funny movie, enjoying a meal or making love can produce a range of feelings from joy to euphoria. Pleasure centers can also be activated artificially.8 For example, a person can temporarily feel on top of the world by drinking a glass of wine because of the release of dopamine, a neurotransmitter discovered in 1958.

The cell membrane, which directs the flow of chemicals in and out of the cells, can be altered by drugs, making it less stable and allowing more chemicals to enter. Therefore, certain chemicals, such as alcohol and cocaine can damage cell function.8

Addiction occurs when the body responds to repeated substance use by increasing its level of resistance to the immediate drug effects and tolerance is developed. While trying to maintain a normal state, the cell membrane is changing, as the receptors and brain chemicals try to help the brain function normally. Eventually, the body is unable to function in the altered state without the drug.

Research has also shown that dopamine plays a role in learning by drawing a person's attention to a particular event associated with past pleasure or reward. Dopamine is now also thought to be a stimulus for behavior…anticipating that pleasure or reward might follow.9 So as a person experiments with a chemical substance and finds it makes him feel good, they are creating a memory of pleasure. So the next time they think about drinking alcohol or using a drug, if the memory of pleasure is now present, they may continue its use. This cycle is described in Figure 2.

Research has shown that the progression to addiction usually occurs in three stages--experimental, tolerance, and dependency. In the initial stage, an individual tries a substance and it feels good. In the second stage, tolerance, an individual may progress to using the substance often, eventually needing more to achieve the original effect. Many people feel embarrassed or guilty at this point. In the third stage, dependency, an individual requires the substance daily. Physical side effects, such as loss of appetite, nutritional deficiencies, infections such as hepatitis, AIDS, and sexually transmitted diseases (since sex is often traded for drugs) are noticeable.