You might have heard probiotic bacteria help keep your gut healthy, but could they be good for your brain, too? A study out this week suggests the answer is yes, at least for mice, because mice on a probiotic diet for a couple of weeks were more relaxed than their counterparts who were not. They showed fewer visible signs of anxiety, lower levels of stress hormones, even chemical changes in the brain. Sounds a little like valium, doesn't it? Other than signals telling you when you're hungry or full, what connection is there between the intestinal tract and the brain? And why would it be there? It's been long known that the brain and the gut communicate. What's becoming clearer over the last while is that this brain-gut communication [is] bidirectional, [and that the microbial] flora within the gut can actually also play an important part in regulating this. So we can now describe what we call the microbial gut-brain axis, and this is coming across in a whole variety of studies in [many new and] different ways. We've known for a long time that if you're feeling sick, or you've got a bad bacteria, like a food poisoning, the [vagus] nerve will signal to the brain to allow you express the sickness behavior. So it's kind of like the good side of what we've already known. We were able to get such a pronounced effect, and similar effects as if the animals had been given some pharmaceutical agents that are used to treat anxiety and depression.