It may make some squeamish, but there are 100 trillion bugs in your intestinal lining. 100 trillion! Believe it or not, these bacteria may actually be your brain's best friends. In part 2 of a series with nutritional coach Zoe Davis, Dr. Daniel Amen and Zoe describe the important ways your gut interacts with your brain, how the vagus nerve just may be to blame for your anxiety and depression.