By: Alli Fries, 3rd year PhD candidate in the Biomedical Sciences Graduate Program
Generally, when people think about neuroscience, the image that comes to mind is the human brain. The brain—an oblong-shaped bulb with grooves and textures, which is reminiscent of a bowl of spaghetti. More ambitious folks might make it past the brain, moving as far as the spinal cord and acknowledging its worth for nervous system functioning. But very few people, if any, think about guts.
That’s right – guts. From start to finish, esophagus to anus, there is a finely-tuned and underappreciated network termed the enteric nervous system —or ENS. Correct functioning of the ENS is key for processes such as digestion, nutrient absorption, and all of the regulation of blood flow and muscle contraction required for these daily events. Impressively, the ENS requires about 100 million neurons (about the same number of neurons as in the spinal cord) to coordinate all of its functions.
Also remarkable, the ENS is capable of operating completely independently of your spaghetti brain. However, for most of the general population, the bi-directional line of communication between your big brain and this little brain is present. Whether or not that communication is working as it should is one subject of study in the field of what is known as “neurogastroenterology.”
Communication from your brain to gut and vice versa occurs along what researchers have termed “the brain-gut axis.” Communication along this axis is accountable for changes in your gastrointestinal tract in response to your mental state, among other things. Have you ever been nervous and felt butterflies in your stomach? Or had a pit in your stomach if you’re upset about something? These events aren’t occurring independently —they are a direct result of your big brain-little brain interactions.
The main phone line between the brain and the gut is the vagus nerve. The vagus collects information from nerve endings located throughout your GI tract and sends information about the local gut environment to your brainstem. The region of your brainstem responsible for receiving and processing this information works a bit like an air traffic controller—there are multiple inputs that need to be sorted and organized to send a signal back down to your gut so that normal digestive processes can occur. The impact of emotional state on how your gut feels is a result of signaling to the brainstem from emotional and stress-related brain regions such as the amygdala, stria terminalis, and hypothalamus.
Medical conditions that are thought to be associated with bad communication between the brain and the gut include many functional gastrointestinal disorders—disorders where your gastrointestinal tract isn’t working properly but there is no obvious physical cause for the symptoms. Interestingly, symptoms of these disorders are often triggered or made worse by any perceived stress. Given the neuronal powerhouse that is your gut, there may be some merit to the idea of a “gut instinct.” We will take a closer look at gastrointestinal function and emotion in future posts.