Origins of Addiction Part 3: Our “Stop” Circuits
A funny thing happened recently - I was worn out after tackling a long day ending in a physically demanding project and it was time to climb in the car and head home. I started up the car and put it in Drive and was surprised as we started to roll forward. I had my foot on the brake and didn’t expect to be moving, so I pushed the brake harder. Instead of stopping, the car engine rev’d even higher and we started moving even faster. By this point I was starting to panic (as was my wife), and out of desperation I punched the Park Button to abruptly stop the car.
Once I calmed down, I figured out what had happened - I was wearing work boots that I don’t usually drive in, and in my tired state I was pushing on both the brake and the accelerator at the same time! The harder I pushed the brake, the harder I was also pushing the accelerator, and my poor car was speeding up and slowing down erratically as these two systems which were not meant to be used together were instead fighting each other to control what happened.
So far in Origins of Addiction, we have focused on understanding how the “Go” circuit works and the role that ancient parts of our brain and nervous system and neurotransmitters such as dopamine play in guiding us to move towards the food we need to survive. As I have said before, the more I learned and reflected on the elegant nature in which our bodies allow us to find food in an environment of scarcity, the more I marveled that we are not all victims of addictive behaviors in the world of abundance that we have created.
Back to my story - the analogy between my car and our bodies is interesting - we do have Go and Stop systems that are constantly in conflict, and the Go system is capable of being much stronger than the Stop. The engine in my car is stronger than the brakes, and if I am artificially revving my engine, the brakes will slip, wear, and even fail. We all know how using substances to energize, soothe, or regulate can spiral up and out of control, and for some of us lead to patterns of seeking behavior that have destructive consequences. We also know that we are each different, both in the strength in which our Go circuit responds to substances, but is that enough to explain addiction? I don’t think so, and my curiosity led me to wonder if addiction can also be thought of as a failure to Stop.
Like with the Go circuit, let’s start with understanding where the simplest of Stop circuits originated - hunger and satiety. The hypothalamus is the part of the brain that senses and responds to various chemical signals, or hormones, from the body and is the primary controller of appetite. When our stomach is empty, it starts releasing a hunger hormone called ghrelin that tells our hypothalamus we should seek food. Our pancreas also detects blood sugar levels, and when they drop insulin levels drop, also telling the hypothalamus to seek food. As we eat, ghrelin levels drop, insulin levels rise, and other hormones are released by the intestines as well, all of which interact with neurons in the hypothalamus to regulate our energy balance. The hypothalamus releases serotonin, which with the other satiety hormones, combine to suppress dopamine and the pleasure/reward we feel from continuing to eat.
Remember our earlier conversations about steering? Those mechanisms evolved 200 million years ago in the earliest of animals and the hypothalamus has long been considered a part of the “ancient” region of the vertebrate brain. More recent research examining simple tadpoles with primitive neural networks of as few as 215 neural cells and mapping the results to equivalent biology in the mouse hypothalamus suggest the hypothalamus predates the evolution of the brain and spinal column as we know them in vertebrates today. (1)
Now that we have some idea of how hunger, satiety, and the brain-gut connection work, let’s think about the go-stop dynamics of drinking an alcoholic beverage. The hypothalamus works just like my car, with an accelerator and a brake, and drinking beer is just like pushing on both the gas and brake in my car. The alcohol starts absorbing into the blood stream quickly, releasing dopamine and increasing appetite, but as my belly fills it starts releasing ghrelin and as the carbs digest into my bloodstream, my pancreas starts releasing insulin and the hypothalamus moves toward satiety.
In my particular case, when I drink beer I have always felt full and satiated before I am intoxicated. Intoxication starts a whole new breakdown in the other Stop circuits which we’ll cover next, but my experience with beer is to get full and stop. In my case, this particular food has stronger brakes than gas, so it has never been a problem for me. Other people with different bodies will have different reaction rates or starting conditions (is your stomach full before you start to drink?), all leading to a different outcome for that person and situation that could be the onset of a deeper physical addiction spiral.
Now let’s turn our attention to the even more complex Stop circuit that evolved much more recently - our pre-frontal cortex (PFC). The PFC is key to our executive function and regulates our behavior; it is where we make plans, choose to not do things we want to do in order to achieve greater goals, control impulses and behavior, and regulate emotions. As described in the last segment, it is where we think “slow” - it’s where we would learn, reason, and decide to live a healthier life with or without alcohol. When it works, it’s a powerful brake on our behavior.
It’s obvious to me how evolving a PFC that can decide and control what to do is naturally pro-survival; we use it to engineer our environments to suit our needs, although often without fully understanding the consequences of those actions. But why would it also evolve to function as a “Stop” circuit? I think the answer is delayed gratification - this is the part of our brain that keeps us from just consuming everything now because of the long term benefit of waiting or the benefit of not waiting. A simple example of this is in foraging for natural food - if we take and eat everything we find, then there will be no crop next year, but if we eat only what we need then there will be more. In the Indigenous canon of principles common across many cultures, this choice is known as the “Honourable Harvest” (2). In the words of science, it is described as the “neural basis of temporal discounting”. (3)
As we are now well aware, the PFC does not mature until 25 or so, and yet we are exposed to and have access to alcohol much earlier than this. Binge drinking and other patterns of use can gain hold without a behavioral Stop circuit to regulate them. Early adulthood is a time of social adolescence, and alcohol use is a way to lower social inhibitions that are forming as we try to fit in and find our place and people in school, work, and society in general. While this may be intentional and beneficial for some, there are also short term and long term consequences to the PFC.
Consuming alcohol impairs the PFC and leads to reduced inhibition, impaired judgment, and increased impulsivity. Short term exposure to alcohol increases dopamine transmission and reinforces the rewarding effects of drinking, leading to more consumption. Long term use leads to physical changes such as reduced dopamine receptors. If this use happens during adolescence, it will actually result in a permanently smaller PFC. Chronic use causes dysregulation in the PFC and cognitive dysfunction, particularly in executive functions like decision making and planning. (4) We may recognize we have a problem, but are now unable to formulate a plan to fix it. We have lost our brakes, perhaps permanently, and abstinence may be the only option for avoiding the chemical and behavioral response to the substance.
Let’s imagine now that we have managed to interrupt this cycle through treatment to interrupt the chemical dependency on a substance by returning to normal dopamine sensitivity. How do we sustain that recovery to feel better knowing that we can’t trust our chemical or behavioral stop circuits to protect us? Again, there are chemical explanations that underpin the behaviors that reinforce long term recovery. Known as the “here and now” hormones, these chemicals differ from dopamine in that they enhance the experience of the present moment. Where dopamine pushes us to want and pursue future goals, the here and now hormones help us regulate mood, form social bonds, alleviate pain, increase feelings of pleasure, and create a sense of well-being.
We’ve already met one of them that is part of the chemical stop circuit - serotonin, which is the mood regulator that leads to feelings of contentment. There is also oxytocin, the “love hormone”, which helps us feel the trust and safety of connection to others. Endorphins are the body’s natural painkillers released in response to pain and stress and causing euphoria - these chemicals are why exercise feels good. And lastly, endocannabinoids - neurotransmitters that evolved more than 500 million years ago before cannabis, contribute to the feeling of pleasure and fulfillment in the present moment. (5) THC, found in cannabis, does not contribute to or release endocannabinoids, but instead they stimulate the CB1 receptors to create the euphoric feeling normally triggered by a release of endocannabinoids by your body.
I am always amazed when new (to me) science intersects with old knowing - I don’t always understand why these two worlds tend to resent each other, but in this case it seems there is much to learn from both about all the factors that can contribute to either successfully avoiding or recovering from substance use disorder with alcohol. It won’t surprise you at all that the activities that release “here and now” hormones in your body are exercise, laughter, meditation, listening to music, social connection, sunlight exposure, and eating certain foods like dark chocolate or spicy dishes. And as DeAnn often says, while recovery starts by healing from the substance, long term recovery is found and sustained by healing the whole self. In the world of recovery, this involves physical, mental, emotional, social, and dietary changes all of which are known to create the calm and present body, mind, and spirit that we associate with spirituality. These two points of view are not in conflict but are in perfect harmony.
References
“The hypothalamus predates the origin of vertebrates”, https://pmc.ncbi.nlm.nih.gov/articles/PMC8081355/
“Braiding Sweetgrass”, Chapter “The Honourable Harvest”, Robin Wall Kimmerer
“Prefrontal Cortex and Impulsive Decision Making”, https://pmc.ncbi.nlm.nih.gov/articles/PMC2991430/
“Alcohol and the Prefrontal Cortex”, https://pmc.ncbi.nlm.nih.gov/articles/PMC3593065/
“People produce endocannabinoids - similar to compounds found in marijuana - that are critical to many bodily functions”, https://sc.edu/uofsc/posts/2023/02/conversation_marijuana.php