Close your eyes and think of your favorite food, maybe it's salt and vinegar chips? Now scan your body for any changes that may have arisen. Is your mouth watering or are you feeling a bit more hungry than you did before? This is a perfect example of how our central nervous system plays a role in our enteric nervous system (the mesh- like system of neurons that governs the function of the gastrointestinal tract). This specific example -as described by Alessio Fasano and Suzie Flaherty in the online book “Gut Feelings" is referred to as the Pavlovian Response- meaning that an outside stimulus like a sound of a word produces an intrinsic response. This portion of the Gut- Brain Axis is widely understood and accepted because it is easy to understand. Think about it! We feel it everyday whether we are hungry after hearing the word “pizza” or not being able to eat before your first day at a new job. It all has to do with the role your brain plays on your stomach. This correlation is also made incredibly clear in the rate of comorbidity of the gastrointestinal disorder- Irritable Bowel Syndrome I.B.S. for short and neurological disorders like Anxiety or Depression. I.B.S. is described as a miscommunication of the neuroendocrine signals and effector nerves inside the GI Tract usually by the perceived stressors in that individual's environment; this could be anxiety brought upon by social factors, or an individual’s behavior or thought patterns (Fasano et al. 2021).

What is a little more difficult to grasp and has just recently been studied is how the Gut- Brain Axis functions in reverse. Meaning how the enteric nervous system can also influence the central nervous system in the same way. Pioneers in the psychological field started by collecting massive amounts of research that connected gut bacteria and neurological disorders such as Autism Spectrum Disorder, Anxiety, Epilepsy, and Parkinson’s just to name a few (Fasano et al. 2021). What all people suffering with these disorders had in common was that the microbiome of their stomach was lacking in biodiversity (Bastiaanssen et al. 2020). Diving deeper into this concept that the G.I. Tract influences the central nervous system through the use of pro and prebiotics. First let us define what pro and prebiotics are. Probiotics are microorganisms that promote gut health and can be found in yogurts or fermented food. Prebiotics are non- digestible food particles that promote the host to create beneficial bacteria in the colon that aids in digestion. Studies suggest that participants who took probiotics to cure their I.B.S. also saw major improvements in their anxiety symptoms as well (Bastiaanssen et al. 2020).

For comparison there are around 500 different species of microflora in the gastrointestinal tract . That is ten times the amount of white blood cells we harness in our body (McEwan et al. 2019). Some experts believe that the close relationship between the gut and brain goes back to our developmental stages. Pertaining to the ectoderm ( one of the three germ levels of an embryo) that is where the formation of both the G.I. Tract and the brain take place. This could give reason to the close functioning or communication of hormonal signals, nerve networks, and endocrine signaling between these two body systems (Fasano et al. 2021)

In conclusion, the importance of these two systems is undeniable for reasons listed above. Think about the major roles these two partake in each other the next time you’re thinking about buying fast food instead of properly preparing a meal or just skipping a meal in general. It could be the difference between a productive day or a lousy one.