Addiction is a psychological and physical inability to stop consuming any substance or stop an activity even though it is causing one psychological and physical harm. It is important we understand the neurobiological processes that lead to addiction as they are the same ones involved in recovery.
Here, I will write on how different parts of the brain are responsible for self-regulation, reward, learning, and memory change and become rewired during repeated substance use. Neurobiology of addiction is basically how these parts of the brain interact with each other as an addiction develops.
The most important neural pathway involved in substance use disorders is the mesolimbic pathway, often called the reward pathway. This pathway controls our response to natural rewards like food, sex, and social interactions. This is the primal or primitive part of our brain in charge of survival.There are a variety of brain chemicals involved in Substance use which include both neurotransmitters and hormones but the one common is a neurotransmitter called dopamine. Dopamine is responsible for supercharging reward-seeking via the ventral tegmental area and the nucleus accumbens. The euphoric feeling one gets when they use a substance is rewarding, right? Dopamine is the neurotransmitter that urges such act to be repeated as the consequences (euphoria) was rewarding.The ventral tegmental area (VTA) releases dopamine based on whether or not environmental stimulants such as drugs, stress, sex, food, or winning a race were rewarding or aversive.
The nucleus accumbens receives the dopamine released by the VTA and mediates the rewarding effects of drugs and stimuli. This is where the fun lives. The pathway from the nucleus accumbens and the amygdala is involved in learning.
Now grab the gist……The brain says this feels good. The pathway from the amygdala to the ventral tegmental area is involved in memory. So the brain says, this felt good last time, and the pathway from the amygdala to the nucleus accumbens is involved in emotional cues from both internal and external triggers.
The brain says these are the conditions that lead to good feelings. The pathways from the prefrontal cortex to many of these areas are involved with higher-order thinking and self-regulation and are referred to as executive functioning.
So the brain might say, I know that this felt really good but it gets in the way of my goals so I won’t do it again. The activation of the mesolimbic pathway tells the individual to repeat what it did to get that reward (euphoria). It also tells the memory centers in the brains to pay attention to all features of that rewarding experience so it can be repeated in the future. So that is how the brain processes, remember, and desires rewarding things, and simply put, drugs are rewarding.
While intoxicating substances including stimulants such as cocaine, and methamphetamine, opioids, and alcohol act in different ways on the mesolimbic system, they all have a lot in common.
Most drugs bind to receptors on neurons within the mesolimbic system either by reducing inhibitory signaling or actively causing dopamine release. Alcohol may be an exception here.
Drugs are dangerous because they cause dopamine release far in excess of what is produced by normal pleasurable stimuli like food, sex, etc., and sends the reward pathway into overdrive. For instance, cocaine increases dopamine release with the burst by a factor of 10! Yeah. That’s crazy, right?
Most brain activity is affected by an individual’s specific genetic makeup and this is certainly true for substance use. Additionally when an individual started using impacts the risk of addiction.
When younger ones start using substances, unfortunately, the more efficient intracellular (communication within a cell) and neuronal communication (communication within a neuron using electrical and chemical signals) work.
This is due to the fact that myelin, a fatty substance like insulation around a battery wire, helps to signal work fast and efficiently and it is produced during several periods in younger life. So what happens with repeated substance use? In short, brain habituation (decrease in response to a stimulus after repeated intake). Overtime, pathways used repetitively become more efficient, require less and less of a stimulus of thought, and create habits, and also are impacted by one’s genetics and age of use. The time it takes to achieve this varies with the kind of drug. Ultimately, the distribution of neurotransmitters gets all out of kilter (out of balance). A person that chronically uses a substance now requires a greater amount of neurotransmitters to activate the reward system. This is what is termed tolerance. Simply put, tolerance occurs when there’s a diminished response to a drug, which occurs when the drug is used repeatedly and the body adapts to the continued presence of the drug.
Studies on animals and humans showed that repeated habitual use changes the number and density of receptors for addictive drugs which is why tolerance develops and changes intracellular signaling molecules and protein expression that are long-term which explains the persistent craving that follows withdrawal.
So what are the consequences of long term drug use? The brain becomes altered chemically and anatomically. The emotional systems of the brain run rapidly and feel out of control. The physical sensation, sensation part of the brain gets badly distorted. The thinking part of the brain, the prefrontal cortex shuts down as the reward system takes over. Everything gets oriented around just trying to feel normal.
But is all hope lost? Obviously not!
The good news is that just as new pathways formed during addiction, the brain can generate new pathways during recovery.
There are evidence-based, cognitive, behavioral, and pharmacotherapies available to help re-calibrate the neural pathways to strengthen pathways to the prefrontal cortex and to weaken pathways to the reward system. In a nutshell, you can remember that during addictions, the reward system, the system that says go, overpowers the prefrontal cortex, the part of the brain that says stop.