How Addiction Happens in the Brain
Addiction specialists and researchers have long known that the process of substance addiction begins when the brain’s pleasure center repeatedly experiences an abnormal buildup of a chemical called dopamine. However, they have not understood why a chronic dopamine buildup produces such dramatic changes in brain function. In a study published in June 2014 in The Journal of Neuroscience, a team of researchers from Brigham Young University looked at the underlying brain mechanisms that trigger the onset of addiction. These researchers concluded that addiction essentially stems from an overreaction to an ongoing form of substance-related damage in the brain called oxidative stress.
Inside the pleasure center, a rise in dopamine levels is responsible for the distinctly pleasing sensations that we experience while doing such commonplace things as eating, having sex and taking part in preferred recreational activities. Consumption of alcohol and a range of drugs and medications also boost the brain’s dopamine levels. However, the dopamine boost associated with drug and alcohol intake is typically far greater than the boost associated with other behaviors. In practical terms, this means that a person who starts using drugs or alcohol has a chance of falling into a pattern of repeated, excessive consumption that stems from a desire to re-experience high levels of pleasure at will.
Over time, recurring exposure to high levels of dopamine changes the way the brain produces and processes this essential chemical. Eventually, dopamine-related alterations can lead to the appearance of physical dependence, a state characterized by a reliance on the continued intake of drugs or alcohol in order to function “normally.” In turn, physical dependence forms the necessary conditions for the appearance of substance addiction, which typically creates additional problems, such as recurring cravings for substance use, loss of voluntary control over substance consumption, prioritization of substance-related activities in everyday life and the development of withdrawal symptoms if the baseline requirements of substance intake go unfulfilled.
Oxidative stress is the term scientists use to describe the harm caused inside the body by naturally occurring and manmade molecules called free radicals. Most people have indirect knowledge of this stress as a result of the popularity of supplements called antioxidants, which help protect the body’s cells from various sources of damage. Forms of oxidative stress-related damage that can occur in the absence of a sufficient amount of antioxidants include cell wall destruction and alteration of the DNA copies stored inside each cell. Apart from addiction-related concerns, health problems associated with oxidative stress include emphysema, certain forms of arthritis, hardening of the arteries, heart attacks and Parkinson’s disease.
Role in Addiction Formation
In the study published in The Journal of Neuroscience, the BYU researchers used laboratory experiments on rats and mice addicted to opioids to explore the underlying reasons for the dopamine-related brain changes associated with the onset of substance addiction. Specifically, they looked at the production of a specialized protein, called BDNF, which the brain releases to counter the effects of oxidative stress. During the study, the rodents were allowed to fall into a state of opioid withdrawal. The researchers then looked for changes in the output of BDNF.
After completing their experiments, the researchers concluded that, during withdrawal, the brain sharply increases its production of BDNF inside the pleasure center. They also concluded that heightened levels of this protein lead to a somewhat lasting decline in the pleasure center’s dopamine levels. Together, these facts indicate that the release of BDNF is directly related to the brain’s attempts to counteract the oxidative stress caused by the presence of excessive dopamine. The researchers concluded that, unfortunately, the brain releases enough BDNF to produce an overcorrection that intensifies withdrawal symptoms and makes it more likely that a substance user will feel the need to consume more drugs or alcohol in order to offset those symptoms. In turn, this increase in consumption further supports the ongoing brain changes that lead to the establishment of an addiction.
The study’s authors also conducted a second study, published in The Journal of Pharmacology and Experimental Therapeutics, which explored the brain changes triggered by the combined use of alcohol and nicotine. In addition, an associate of the authors conducted a third study, published in the journal Addiction Biology, which explored the brain changes triggered by the use of cocaine. Like the study published in The Journal of Neuroscience, both of these studies identified the dopamine-related alterations that help set the stage for substance addiction.