Drugs tap into the brain’s communication system and disrupt the way nerve cells normally send, receive, and process information. There are at least two ways that drugs are able to do this: (1) by imitating the brain’s natural chemical messengers, and/or (2) by overstimulating the “reward circuit” of the brain.
Some drugs, such as marijuana and heroin, have a similar structure to neurotransmitters, the chemical messengers naturally produced by the brain. Because of this similarity, these drugs are able to “fool” the brain’s receptors and activate nerve cells to send abnormal messages.
Other drugs, such as cocaine or methamphetamine, can cause the nerve cells to release abnormally large amounts of natural neurotransmitters, or prevent the normal recycling of these brain chemicals, which is needed to shut off the signal between neurons. This disruption produces a greatly amplified message that ultimately disrupts normal communication patterns.
Nearly all drugs, directly or indirectly, target the brain’s reward system by flooding the circuit with dopamine. Dopamine is the neurotransmitter present in regions of the brain that controls movement, emotion, motivation, and feelings of pleasure. The overstimulation of this system, which normally responds to natural “survival type” behaviors (eating, spending time with loved ones, etc.), produces euphoric effects in response to the drugs. This reaction sets in motion a pattern that “teaches” people to repeat the behavior of abusing drugs.
As a person continues to abuse drugs, their brain adapts to the overwhelming surges in dopamine by producing less dopamine or by reducing the number of dopamine receptors in the reward circuit. In order to bring their dopamine function back to normal or to achieve the same dopamine high, they require even larger amounts of the drug. Tolerance can lead to long-term abuse which further alter the brain’s chemical systems and circuits.
Glutamate is a neurotransmitter that influences the reward circuit and the ability to learn. When the optimal concentration of glutamate is altered by drug abuse, the brain attempts to compensate. This can impair cognitive function. Drugs of abuse facilitate nonconscious (conditioned) learning, which leads the user to experience uncontrollable cravings when they see a place or person they associate with the drug experience, even when the drug itself is not available.
Brain imaging studies of drug-addicted individuals show changes in areas of the brain that are critical to judgment, decision-making, learning, memory, and behavior control. Together, these changes can drive an abuser to seek out and take drugs compulsively despite adverse consequences–in other words, to become addicted to drugs.
Source: NIDA: National Institute on Drug AbuseTags: addiction, the brain and drugs Posted by