We know that the intestines play a critical role in influencing our physical health. Issues associated with gut inflammation, such as diverticulitis, food sensitivities, and obesity, are widely acknowledged in the scientific and medical communities. More recently, however, biologists have become fascinated with “gut microbiota” and how bacteria that dwell in our intestinal tissues communicate with our brains, thereby influencing our thoughts, feelings, and behaviors. Specifically, research reveals that our guts impact our levels of anxiety, emotional stability, cognition, and pain (Cryan and Dinan, 2012).
NPR published a piece this week revealing how bacteria in the gut may influence our mental processes (Stein, 2013). In it, Dr. Emeran Mayer, a professor of medicine and psychiatry at UCLA, discusses his current research: examining MRI scans of thousands of volunteers and comparing the structures of their brains to the strains of bacteria in their intestines. He has observed significant links between the types of gut bacteria and the regions of the brain to which they correspond. Basically, this suggests that our brain chemistry will differ based on the specific gut microbiota present in our systems.
To explore this notion further, other researchers have studied the influence of different types of gut bacteria on the anxiety levels of mice (Collins, Kassam, and Bercik, 2013). The results were intriguing; mice which were identified as anxious and fearful became less so when their intestinal bacteria were replaced with those of the mice identified as “fearless.” And the same outcome was observed in reverse; the mice identified as fearless became more fearful and hesitant when their gut bacteria were replaced with those of the anxious mice.
Researchers in Ireland, meanwhile, have identified the vagus nerve as the primary channel between the abdomen and the brain. When they cut this particular nerve in laboratory mice, their guts ceased to communicate with their brains (Cryan and Dinan, 2012). According to their research, gut microbiota may also send messages to the brain via neurotransmitters and immune pathways. This is a fairly sizable network, so the gut-brain connection is significant in terms of developing new treatments and approaches to both mental and physical health conditions.
As was shown with the fearful and fearless mice, conditions such as anxiety may be connected to the type of bacteria a person is housing in his or her gut (Collins, Kassam, and Bercik, 2013). So if a person is receiving persistent messages from the gut to “be afraid, be very afraid” when there are no imminent signs of danger, then perhaps that person should consider balancing his or her intestinal bacteria rather than honoring their microbial anxious cries.
In light of such findings, scientists are increasingly acknowledging that probiotics, which have long been touted as beneficial for maintaining healthy gut flora, may have an important part to play in mental as well as physical health. Current research is looking at the effects of “good bacteria” on conditions such as bipolar and autism. The results of these studies are largely yet to be seen, although some positive results have been documented regarding anxiety in response to probiotics (Stein, 2013).
Ultimately, studies such as these help to explain the gut’s reputation as the second brain. Most people have likely heard someone tell them to “follow your gut instinct” or “listen to your gut.” However, when determining whether to listen to what yours is telling you, you may want to keep in mind that there are varying strains of intestinal bacteria—potentially all of them capable of communicating with your brain—and some may have more beneficial things to say than others.
- Collins, S. M., Kassam, Z., and Bercik, P. (2013, June). The adoptive transfer of behavioral phenotype via the intestinal microbiota: experimental evidence and clinical implications. Current Opinion in Microbiology, 16(3), 240–245. Abstract retrieved from http://www.sciencedirect.com/science/article/pii/S1369527413000787
- Cryan, J. F., and Dinan, T. G. (2012, October). Mind-altering microorganisms: The impact of the gut microbiota on brain and behavior. Nature Reviews Neuroscience, 13, 701–712. doi: 10.1038/nrn3346. Abstract retrieved from http://www.nature.com/nrn/journal/v13/n10/abs/nrn3346.html
- Stein, R. (2013, November 18). Gut bacteria might guide the workings of our minds. NPR. Retrieved from http://www.npr.org/blogs/health/2013/11/18/244526773/gut-bacteria-might-guide-the-workings-of-our-minds
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