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Just as we turn down the volume on a radio that is too loud, the brain adjusts to the overwhelming surges in dopamine (and other neurotransmitters) by producing less dopamine or by reducing the number of receptors that can receive and transmit signals. As a result, dopamine’s impact on the reward circuit of a drug abuser’s brain can become abnormally low, and the ability to experience any pleasure is reduced. This is why the abuser eventually feels flat, lifeless, and depressed, and is unable to enjoy things that previously brought them pleasure. Now, they need to take drugs just to bring their dopamine function back up to normal. And, they must take larger amounts of the drug than they first did to create the dopamine high – an effect known as tolerance.

How does long-term drug taking affect brain circuits?

Drugs are chemicals. They work in the brain by tapping into the brain’s communication system and interfering with the way nerve cells normally send, receive, and process information. Some drugs, such as marijuana and heroin, can activate neurons because their chemical structure mimics that of a natural neurotransmitter. This similarity in structure “fools” receptors and allows the drugs to lock onto and activate the nerve cells. Although these street drugs mimic brain chemicals, they don’t activate nerve cells in the same way as a natural neurotransmitter, and they lead to abnormal messages being transmitted through the network.

Other drugs, such as amphetamine or cocaine, can cause the nerve cells to release abnormally large amounts of natural neurotransmitters or prevent the normal recycling of these brain chemicals. This disruption produces a greatly amplified message, ultimately disrupting communication channels. The difference in effect can be described as the difference between someone whispering into your ear and someone shouting into a microphone.

How do drugs work in the brain to produce pleasure?

All drugs of abuse directly or indirectly target the brain’s reward system by flooding the circuit with dopamine. Dopamine is a neurotransmitter present in regions of the brain that regulate movement, emotion, cognition, motivation, and feelings of pleasure. The over stimulation of this system, which rewards our natural behaviors, produces the euphoric effects sought by people who abuse drugs and teaches them to repeat the behavior.

This information about smokers cravings was recently released from Duke University:

Brain scans of smokers studied by the researchers revealed three specific regions deep within the brain that appear to control dependence on nicotine and craving for cigarettes. These regions play important roles in some of the key motivations for smoking: to calm down when stressed, to achieve pleasure and to help concentration.

“If you can’t calm down, can’t derive pleasure and can’t control yourself or concentrate, then it will be extremely difficult for you to break the habit,” said lead study investigator Jed E. Rose, Ph.D., director of the Duke Center for Nicotine and Smoking Cessation Research. “These brain regions may explain why most people try to quit several times before they are successful.”

In this study, the researchers manipulated the levels of nicotine dependence and cigarette craving among 15 smokers and then scanned their brains using positron emission tomography, or PET scans, to see which areas of the brain were most active.

Three Regions of the Brain are Important for Smokers

Three specific regions of the brain demonstrated changes in activity when the smokers craved cigarettes versus when they did not.

One region that lights up, called the thalamus, is considered to be the key relay point for sensory information flowing into the brain. Some of the symptoms of withdrawal among people trying to quit stem from the inability to focus thoughts and the feeling of being overwhelmed, and could thus be explained by changes in this region, according to the researchers. The researchers found that changes in this region were most dramatic among those who said they smoked to calm down when under stress.

Although taking drugs at any age can lead to addiction, research shows that the earlier a person begins to use drugs the more likely they are to progress to more serious abuse. This may reflect the harmful effect that drugs can have on the developing brain.

Research has shown that the key risk periods for drug abuse are during major transitions in childrens lives. The first big transition for children is when they leave the security of the family and enter school. Later, when they advance from elementary school to middle school, they often experience new academic and social situations, such as learning to get along with a wider group of peers. It is at this stage early adolescence that children are likely to encounter drugs for the first time.

When they enter high school, adolescents face additional social, emotional, and educational challenges. At the same time, they may be exposed to greater availability of drugs, drug abusers, and social activities involving street drugs. These challenges can increase the risk that they will abuse alcohol, tobacco, and other substances.

Researchers studying the effects of alcohol use on the brain are aided by advanced technology such as magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), positron emission tomography (PET), and electrophysiological brain mapping. These tools are providing valuable insight into how alcohol affects the brains structure and function.

Long term heavy drinking may lead to shrinking of the brain and deficiencies in the fibers (white matter) that carry information between brain cells (gray matter). MRI and DTI are being used together to assess the brains of patients when they first stop chronic heavy drinking and again after long periods of sobriety, to monitor for possible relapse to drinking.

Memory formation and retrieval are highly influenced by factors such as attention and motivation. Studies using MRI are helping scientists to determine how memory and attention improve with long-time abstinence from alcohol, as well as what changes take place when a patient begins drinking again. The goal of these studies is to determine which alcohol induced effects on the brain are permanent and which ones can be reversed with abstinence.

The American Psychiatric Association says that a person is addicted if their pattern of substance use leads to clinically significant impairment or distress shown by three or more of the following in a 12-month period:

1. Tolerance as defined by any of the following:

* a need for markedly increased amounts of the substance to achieve intoxication or desired effect
* markedly diminished effect with continued use of the same amount of the substance

2. Withdrawal, as manifested by either of the following:

* the characteristic withdrawal symptom of the substance
* the same or a closely related substance is taken to relieve or avoid withdrawal symptoms

3. The substance is often taken in larger amounts or over a longer period than was intended (loss of control)

4. There is a persistent desire or unsuccessful efforts to cut down or control substance use (loss of control)

Two of the symptoms of drug addiction usually include mood swings and irrational behavior.

Brain chemistry is crucial to the optimal function of the brain and body. Research shows that many addictive people have a brain disorder.