Reader, thanks to the proliferation of the smartphone and the tablet, and the advent of the Attention Economy, our society has perhaps never been more inundated by diversion. Children playing games on their parents’ tablets everywhere from the restaurant to the grocery store has become a common sight to see—and nowadays, it’s stranger to see an adult engaged in a book or a newspaper on a train than it is to see one playing on their phone to pass the time. Games once played in person can now be played virtually, with someone halfway around the world. Call me old fashioned, but I believe there is still something to be said for the kinds of games that come in a box, played on a board. I fondly recall the board games I used to play with my daughters, because each of the classics requires a different type of analytical thinking. To engage our brain’s capacities for planning and foresight, there is no better game than chess. To engage in problem-solving and strategic thinking, there is Mancala. And to engage our brains in the understanding of how one action leads to another? For that, reader, there is no game better than Mouse Trap!
Mouse Trap is the game of building the chain reaction—and in this way, it is the perfect metaphor for the thousands of processes our bodies engage in moment to moment, day to day. We are products of countless actions and chain reactions that both determine our health and also impact our mindset—and even our personality. Many of these chain reactions are composed and orchestrated by our DNA. Of course, if you’ve been following this series, you know our personal genome is not the only player in the game. Our microbiomes play a significant role in starting chain reactions that can have a big impact on our mental health. And recent research has demonstrated that our gut bugs may be implicated in the chain reaction leading to one of the most ubiquitous mental health concerns among children today: Attention-Deficit/Hyperactivity Disorder. What is the role our gut bugs play—and what can we do about it? Let’s dig in to find out!
What is ADHD—And How is the Microbiome Involved?
ADHD effects approximately 6% of US children, making it one of the most prevalent neurodevelopmental and neurobehavioral disorders. Despite its frequency, we know strikingly little about its underlying causes. ADHD is commonly characterized by hyperactivity and impulsivity, inattentiveness, or a combination of all three—however, like autism, this is a heterogeneous disease that can look very different from patient to patient. That said, there are a few hallmarks of ADHD displayed by a large swath of patients with this disorder—and two can be directly tied back to the microbiome.
First and perhaps most familiar to frequent readers of this blog: patients with ADHD frequently display increased incidence of gastrointestinal issues. This is very much aligned with other mental illnesses covered in this series, from depression to bipolar disorder to autism and beyond. Let’s review what we know about GI issues and their connection to mental health: First, we know our microbiomes and brains are intricately interconnected through the “Gut Brain Axis”, and that our gut bugs can “speak” directly to our nervous system and other bodily systems via the passage of various metabolites, hormones, and other “messenger” compounds from our intestinal tract into our bloodstream. Second, we know that the messages sent from a dysregulated microbiome—a “leaky gut”, that is—are different than the messages sent from a healthy microbiome. And third, we know that the toxins and bad gut bugs found in a gut in dysbiosis can lead to inflammation and trigger an autoimmune response that has further impact on our mental health. Patients with ADHD regularly suffer with immune dysregulation, low-grade inflammation, and a leaky gut—all three of the warning signs that the microbiome is sending bad signals to the brain.
The consequences of a dysregulated gut, of course, are the most obvious ways the microbiome may be implicated in ADHD. But gut bugs are also increasingly implicated in another significant hallmark of the disorder—like the game of Mouse Trap, they may begin a chain reaction that leads directly to a hallmark trait of ADHD: a dysfunction of the brain’s reward pathway.
A Chain Reaction: Gut Bugs, ADHD, Dopamine, and the Brain
Patients suffering from ADHD demonstrate dysfunction in their brain’s reward pathway. This pathway plays a critical role in “reinforcement, motivation, and learning how to associate various stimuli with reward”—and to function properly, it relies almost entirely on our body’s supply of dopamine. Here’s how it works: when we engage in activities that are beneficial to our survival—like drinking, eating, and reproduction—dopamine is released. As we’ve discussed before on this blog, dopamine is a “feel good” or “pleasure” chemical. It makes us feel joyful and euphoric, and in terms of our reward pathway, feeling good after we partake in an activity leads to a desire to partake in it again and again.
Now, here’s where things get interesting. The dopamine release that keeps our reward system pathway regulated is just the end of a long chain reaction of circumstances—and that chain reaction begins in the microbiome. Researchers studying the microbiome have found that patients with ADHD display elevated levels of Bifidobacterium compared to patients without the disease. These increased numbers of gut bugs begin the chain reaction. Bifidobacterium DNA creates an enzyme called CDT, which in turn helps manufacture the amino acid phenylalanine, which subsequently makes dopamine—and dopamine, finally, helps us regulate our body’s understanding of reward, incentive, motivation, and positive reinforcement. Whew!—that’s quite the Mouse Trap if you ask me—and it all starts in the gut.
Researchers have found that increased Bifidobacterium is the origin point for a dysregulated dopamine/reward pathway—and you can understand why, given its intricate relationship to the process of dopamine creation. And if ADHD lives at least in part in the gut, then that opens the doors to revolutionary methods of treatment that could offer millions of patients relief from their symptoms.
Within the microbiome, there is incredible potential for treatment, healing, and recovery. Our gut bugs play an important role in the chain reactions that lead to mental health outcomes—and understanding their delicate interplay with other bodily systems will be an important element of the future of precision medicine.
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