That Neuroscience Guy - The Neuroscience of Gut Health

Episode Date: February 7, 2024

Sometimes we talk about "going with your gut" when making decisions that feel right. As it turns out, our intestines are actually highly linked to our brain in more ways than just an expression. In today's episode of That Neuroscience Guy, we discuss the Gut-Brain Axis - a system linking our digestive system to our nervous system. 

Hi, my name is Olaf Krigolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. You might have heard that you have a brain in your gut. Well, it turns out that you do, sort of. Indeed, you might have made a decision based on a gut hunch or felt butterflies in your stomach when you're anxious. So on today's podcast, the gut-brain axis.

This second brain has a more formal name, and that is your enteric nervous system. The NS is basically two thin layers of more than 100 million nerve cells lining your gastrointestinal tract from your esophagus to your rectum. The enteric system neurons can be classified in three main groups. There are intrinsic primary afferent neurons. These are neurons that bring in sensory information. There are interneurons, which connect the different parts of the enteric nervous system together. And there are motor neurons. Like I said, the intrinsic primary afferent neurons detect chemical and mechanical stimuli from ingestion, usually food and drink.

drink. The motor neurons in the enteric nervous system are responsible for coordinating peristasis, rhythmic muscle contractions, and move material along the digestive tract. In the interneurons, we've talked about in the past, but basically interneurons pass signals from the afferent neurons to the motor neurons, and they also coordinate with other parts of the nervous system. Enteric neurons can regulate the vomiting reflex, which is particularly critical in those cases in which vomiting arises as a side effect of medical treatments, including chemotherapy. But before we get going more, let's quickly review. Your central nervous system is basically your brain and your spinal cord,

and that's what we think of as your brain, right? Your brain is the key part of the central nervous system is basically your brain and your spinal cord. And that's what we think of as your brain, right? Your brain is the key part of the central nervous system. You can't rule out the parts of it like the spinal cord, because that's how communication is passed throughout the body. And the peripheral nervous system is basically all of the nerve stemming out from the CNS to control muscles or bring in sensory information, etc. Now, the main role of the enteric nervous system is controlling digestion from swallowing to the release of enzymes that help break down food

to the control of blood flow that helps with nutrient absorption to elimination. The enteric nervous system doesn't seem capable of thought as we know it, but it communicates back and forth with our brain, with profound results. So for example, the enteric nervous system is not going to help you decide what to eat for lunch or what movie you want to see, but it may influence these decisions in a sense. A traditional point of view proposed that conditions such as depression may lead to gastrointestinal issues, but more recently, research suggests that at least part of the time it can be the other way around.

Specifically, having gastrointestinal issues may trigger the enteric nervous system to send messages to the central nervous system. These new findings may explain why a higher than normal percentage of people with IBS, irritable bowel syndrome, and functional bowel problems develop depression and anxiety. That's important data because up to 30 to 40 percent of the population has functional bowel problems at some point in their lives. So basically, if you have bowel disruptions, as an example of one of the issues you might have in your gastrointestinal system, this might actually be influencing your central nervous system and cause things, like I said, like depression and anxiety. So an altered gut microbiota, also known as

intestinal flora, has been linked to mental illness, such as depression and some neurodegenerative diseases, including Alzheimer's and Parkinson's disease. Our understanding of the ENS, enteric nervous system, to central nervous system connection helps explain the effectiveness of irritable bowel syndrome and bowel disorder treatments as antidepressants and mind-body therapies like cognitive behavioral therapy and medical hypnotherapy on helping also treat some of these more internal problems. So there's this back and forth between the enteric nervous system and the central nervous system. So basically research shows that the enteric and central nervous system communicates back

and forth with each other and it's not one way as previously thought. It's now pretty well accepted that the enteric nervous system is sending messages back up, where in previous years, people thought that, hey, this signal was just one way, and it was sent down. Now, research suggests that the digestive system, so the enteric nervous system, may also affect cognition, thinking skills, and memory. So this thing isn't just signaling things that might be bad, such as depression, anxiety, but it can have an impact on our cognitive skills. And this can be positive or negative. Sometimes cognitive skills are

facilitated, and sometimes they'd be impaired. So how does it all work? Basically, what it all boils down to is microbial diversity. Microbes are tiny living things that are found all around us and are too small to be seen by the naked eye. They live in the water, the soil, and in the air. And the human body is also home to millions of these microbes too, also called microorganisms. Now some microbes make us sick, but others are important for our health. Now the most common forms of microbes are bacteria, viruses, and fungi. There are also microbes called protozoa. These are tiny living things that are responsible for diseases such as toxoplasmosis and malaria. Now, bacteria are single-cell organisms.

Some bacteria need oxygen to survive and others do not. Some love the heat, while others prefer a cold environment. Well-known examples of bacteria include salmonella and staphylococcus bacteria. And it's important to think that bacteria aren't as simple as they might be. There's actually some cool new research that suggests that these single-celled organisms might even have a sense of touch. Now, most bacteria aren't dangerous for humans. Many of them even live on or in our body and help us to stay healthy. For instance, lactic acid bacteria in the bowel

help us digest food. Other bacteria help the immune system by fighting germs. Some bacteria also need an order to produce certain types of food, on a different note, like yogurt, sauerkraut, or cheese. Indeed, less than 1% of all bacteria are responsible for diseases, but it is just a rough estimate because there are no exact numbers. Tuberculosis, for instance, is caused by bacteria. Bacterial infections can be treated with antibiotics, but these medicines that kill bacteria basically stop them from multiplying. Sometimes they kill them as well. Many other infections, including diarrhea, colds, or tonsillitis, can be caused by bacteria, but viruses are usually responsible for them. Antibiotics aren't effective against viruses in general, though.

So they do work against bacteria, but not viruses. So it's not a good idea to start using them too soon if it's only suspected that bacteria are causing the infection. So let's get back to the gut-brain connection. Basically, the entire enteric nervous system generates bacteria, but typically we refer to these as microbes, which it then releases into the body. Disruptions in the system lead to negative issues such as irritable bowel syndrome, but this release can also impact cognitive function and cause issues such as depression. Again, this bottom-up connection. It's important to note that the enteric nervous system can have a positive impact on the body and brain as well. For example, the messages from the enteric nervous system can have a positive impact on the body and brain as well. For example,

the messages from the enteric nervous system can be used as warning signals that something's wrong. So basically the brain can listen to the enteric nervous system and the signals that come up, it can go, well, hang on, we need to change something here because if we continue the way we are, something's going to, bad is going to happen, or something bad that's happening is going to get potentially worse. To date, more research is investigating the positive impact of the enteric nervous system. It's still not really that well understood. Although, beware, because there's a lot of stuff out there about the gut-brain connection,

and it's important to do your own research to separate what's true from what's just a hopeful claim. Now, on that note, I usually like to give tips on how to help with things, in this instance, to ensure good function of the enteric nervous system, how to improve your gut-brain connection. Basically, I have to emphasize, if you do have gastrointestinal issues, you need to work with a medical doctor to resolve them. Sometimes they're treated with a change in diet. And if it's that simple, that's great. But sometimes you'll need medical treatment. So if you do have problems with your gastrointestinal system, it's important to talk to your doctor. And of course, my usual mantra, things that improve

function of not just the brain, but your body and your nervous system in general, sleep, diet, and exercise. You can't get around a good night's sleep. You can't get around a healthy diet and you can't get around exercise. If you are having problems with your enteric nervous system or the brain in general, or basically anything else with your body, sleep, diet, and exercise are really the best cure. That's all I have on the gut-brain axis. Thank you for listening. Hopefully you found it interesting.

Don't forget the website, thatneuroscienceguy.com. There's links to our Etsy store. There's links to Patreon where you can support us. We had 10 new people start supporting us recently. Thank you so much. All of the money goes to graduate students in my lab. Even a dollar a month makes a difference, believe it or not. And of course, if you have ideas, this one came from you, the listeners. We really want to know what you want to know about the neuroscience of daily life. So send me a direct message on threads or X at

that neuroscience guy or email us at that neuroscience guy at gmail.com. And of course, thank you for listening to the podcast. Please subscribe. My name is and I'm that neuroscience guy. I'll see you soon for another neuroscience bite.