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Drugs and Our Brains

November 21, 2014  |  Falmouth Enterprise

Dr. Michael Bihari

The brain is the most complex organ in the human body. Our brains regulate our body’s basic functions; enable us to interpret and respond to everything we experience; and shape our thoughts, emotions, and behavior. We need our brains to do school work, function at our jobs, drive a car, enjoy a meal, breathe, be creative, and enjoy everyday activities. 

The following information is adapted from “The Brain on Drugs: The Science of Addiction” published online by the National Institute on Drug Abuse.

The Parts of the Brain

The brain is made up of many parts that all work together to coordinate and perform specific functions. Drugs can alter several important areas of our brains that are needed for life-sustaining functions and can drive the compulsive drug abuse that marks addiction. Brain areas affected by drug abuse include:

The brain stem controls basic functions critical to life, such as heart rate, breathing, and sleeping.

The cerebral cortex processes information from the senses, allowing us to see, feel, hear, and taste. The front part of the cortex (the frontal cortex) is the thinking center of our brains; it powers our ability to think, plan, solve problems, and make decisions.

The limbic system links together a number of brain structures that control and regulate our ability to feel pleasure. Feeling pleasure motivates us to repeat behaviors that are critical to our existence such as eating, sex, and socializing. The limbic system also is activated by drugs of abuse. And, the fact that the limbic system is responsible for our perception of other emotions, both positive and negative, explains the mood-altering properties of many drugs.

How the Parts of the Brain Communicate

The brain is a complex communications center consisting of billions of nerve cells. Networks of nerve cells pass messages back and forth among different structures within the brain, and with nerves in the rest of the body. These nerve networks coordinate and regulate everything we feel, think, and do.

Each nerve cell in the brain sends and receives messages. To send a message, a nerve cell releases a chemical (neurotransmitter) into the space (synapse) between it and the next nerve cell. The neurotransmitter crosses the synapse and attaches to a receptor on the receiving brain cell. This causes changes in the receiving cell—the message is delivered and our body acts accordingly.

How Drugs Work in the Brain

Drugs affect the brain by tapping into its communication system and interfering with the way nerve cells normally send, receive, and process information. 

Most drugs of abuse (such as marijuana, heroin, hydrocodone, and cocaine) target the brain’s reward system by flooding the circuit with dopamine. Dopamine is a neurotransmitter present in regions of our brains that regulate movement, emotion, motivation, and feelings of pleasure. When activated at normal levels, this system rewards our natural behaviors. However, overstimulating the system with drugs of abuse produces euphoric effects, which can strongly reinforce the behavior of drug use—teaching the user to repeat it.

Our brains are wired to ensure that we will repeat important life-sustaining activities 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, and teaches us to do it again and again without thinking about it. Because drugs of abuse stimulate the same circuit, we learn to abuse drugs in the same way.

When some drugs of abuse are taken, they can release two to ten times the amount of dopamine than natural rewards such as eating and sex do. Sometimes, this occurs almost immediately (as when a drug is smoked or injected), and the effects can last much longer than those produced by natural rewards. The resulting effects on the brain’s pleasure circuit dwarf those produced by naturally rewarding behaviors. The effect of such a powerful reward strongly motivates people to take drugs again and again. This is why scientists sometimes say that drug abuse is something we learn to do very, very well.

Long-term Drug Abuse Impairs Brain Functioning

For the brain, the difference between normal rewards and drug rewards can be described as the difference between someone whispering into your ear and someone shouting into a microphone. Just as we turn down the volume on a radio that is too loud, the brain adjusts to the overwhelming surges in dopamine by producing less dopamine or by reducing the number of receptors that can receive signals. As a result, dopamine’s impact on the reward circuit of the brain of someone who abuses drugs can become abnormally low, and that person’s ability to experience pleasure is reduced.

This is why a person who abuses drugs eventually feels flat, lifeless, and depressed, and is unable to enjoy things that were previously pleasurable. Now, that person needs to keep taking drugs again and again just to try and bring his or her dopamine function back up to normal—which only makes the problem worse. And, the drug user will often need to take larger amounts of the drug to produce the familiar dopamine high—an effect known as tolerance.

Long-term drug abuse also can cause conditioning, a type of learning in which cues in a person’s daily routine or environment become associated with the drug experience and can trigger uncontrollable cravings whenever the person is exposed to these cues, even if the drug itself is not available. This learned “reflex” is extremely long-standing and can affect a person who once used drugs even after many years of abstinence.

Chronic abuse of drugs can disrupt the way the brain controls and inhibits behaviors related to drug use. Just as continued abuse may lead to tolerance or the need for higher drug dosages to produce an effect, it may also lead to addiction, which can drive a user to seek out and take drugs compulsively. Drug addiction erodes a person’s self-control and ability to make sound decisions, while producing intense impulses to take drugs.

Recommended Resource

NIDA for Teens: Brain and Addiction: An excellent and clear explanation of how the teen brain works and is affected by drug use.

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