Every thought, emotion or action one experiences involves the nervous system. This system includes the brain, spinal cord and nerves that extend throughout the body. To regulate thinking, feeling and action, the brain has to be more complex and flexible than any computer developed. The brain accomplishes its multiple tasks through the use of electrical charges and chemicals. Neurotransmitters are one of the main chemicals that the brain utilizes. The end result of the brain's use of these electrical impulses and chemicals are new responses from glands, organs and muscles. This also results in changes in emotions and behavior. Main neurotransmitters involved in the changes that the brain experiences with substance dependence include dopamine ~ serotonin ~ endorphins.
The main areas of the brain that are affected by neurotransmitters include the mesolimbic system, which is involved in the ability to feel pleasure. The use of substances can have the effect of intense feelings of pleasure. The hypothalamus controls survival in humans and other animals. Behaviors that are regulated include eating, drinking and sexual activity. The medial forebrain bundle is a nerve pathway. If this bundle is stimulated by an electrical charge of chemicals, one feels intense pleasure or euphoria. This is the type of stimulation produced by mind-altering drugs. Repeated exposure or stimulation of this pathway creates a compulsive need/want, which is thought to be a part of the compulsion that people with chemical dependence experience, making abstaining a difficult behavioral change.
The brain modifies connections in response to experience. When a person learns something or has a new experience, new synapses may form. When a person takes drugs repeatedly, the brain changes in response to this experience. He will crave the drug. Tolerance is when the brain has adapted to having a certain amount of drug present and does not respond the same way it did initially. That is why drug abusers and addicts take increasingly higher amounts of an abused drug. One of the most dramatic long-term effects of a drug is killing neurons. Alcohol kills brain cells. Amphetamines kill neurons that produce serotonin, a neurotransmitter that regulates appetite, sleep, emotions and so on. Cocaine changes the brain in ways that may last for a long time. Two years after the last use PET images show that the drug abuser's brain is less active.
Scientists don't know all of the effects that a drug may have. The brain is such a complicated organ. Individuals may respond differently to drugs due to genetic differences. Many drug abusers abuse more than one drug and the combination makes it difficult to determine what the effect of one drug alone may be. Drug addicts often suffer from mental illnesses, such as depression. The changes that occur in the brain because of mental illness make it difficult to determine what changes the drugs have caused. Someday scientists will answer questions about what happens in the brain to cause additiction, which will then help them understand how to prevent addiction.