There is a “second brain” in your gut.

If you’ve ever heard the phrase “I’ve got a gut feeling about this,” if you’ve felt butterflies in your stomach, or even if you’ve felt something in your gut when you’ve just received horrible news, this should shed a whole new light. The neural tissue in the gut, filled with neurotransmitters, partly determines the mental state. 

Technically known as the enteric nervous system, this “second brain” is made up of 100 million neurons in the lining of the gut, from esophagus to anus. It even has more neurons than the spinal cord. These neurons are what allow us to get that feeling of butterflies, or the feeling associated with terrible news. 

Though the “second brain” doesn’t control thoughts on logic, philosophy, etc., it does have its own senses and controls behavior apart from the brain (namely digestion). It’s even thought that the “second brain” sends messages to the brain on emotional well being. 

Many think this ties into a more direct link to the food you eat having effects on your mood. Scientists also believe this “second brain” plays a role in certain diseases. The entire study which elaborates on the topic can be read here 

(Source)