字幕表 動画を再生する 英語字幕をプリント If you've ever had a “gut reaction” to something, gone with a “gut feeling” or had a “gut-wrenching” experience; you may not realise we use these terms for a reason. In our gut lies our enteric nervous system and it’s often called our second brain. We have the same number of neurons lining our long tube of gut as we do in our spinal cord. And our gut is capable of reacting, like causing cravings for a taco, without even communicating with our first brain. We have a community of bacteria living in our gut called our microbiome. It’s influenced by what you eat, your genes, age, stress levels and even where you live. Certain bacteria thrive depending on what you eat, and we’re just starting to realise what it can do. Our microbiome can communicate with our Central Nervous System and influence our behaviour. In one study, germ-free mice, who aren't exposed to any bacteria since birth and don’t develop a microbiome, were compared to their germ-carrying counterparts in a maze test. The germ-free mice showed a reduction in anxiety-like behaviors in response to the maze. They were then housed with the other mice, and exposed to their germs. But when they did the maze test again, they still showed a reduction in anxious behaviour. The researchers suggested gut-brain interactions are important to the development of stress systems, and the germ-free mice missed their window to develop one. A recent study found that prebiotics, little fibre compounds that stimulate the growth of gut bacteria, have an anti-anxiety effect in people. Participants were split into two groups, one that took prebiotics every day, and one that took a placebo. After three weeks, those who took prebiotics had lower levels of the stress hormone cortisol and in tests they paid less attention to negative information and more attention to positive information. And other studies have shown that giving people fermented milk products containing probiotics, or healthy bacteria, twice a day for four weeks, altered brain activity in regions linked to emotion. The function of our gastro-intestinal tract goes far beyond just processing what we eat. Of course our second brain, our enteric nervous system, isn’t capable of conscious thought. But our microbiome can influence our behavior, our stress levels and even our mood. So the next time you have that feeling of butterflies in your stomach, remember there’s a whole lot more happening down there than you may realise. For more awesome facts about yourself, head over to my friends Alltime Numbers, where they’ll take you through the human body in numbers. And if you don’t already subscribe to BrainCraft! For a new, brainy video every Thursday.