A new study provides more evidence that there is a deep connection between our gut and our brains. The findings suggest that probiotics -- so-called good bacteria that aid in digestion -- may also help to lessen symptoms of depression. There are about 300 to 500 bacterial species that live in the human gut. Many help with digestion and keep the gastrointestinal system working right. Scientists say these probiotics play a part in neural activity that controls digestion. In addition, there is also new evidence that shows probiotics can also affect a person's mental state, or mood.