People say, “we are not alone” to indicate that extraterrestrials are out there, and some often wonder if someday extraterrestrials will take over our world. The notion that other life forms are obsessed with controlling humans has been a common theme in science fiction for more than 100 years. Evolving research argues that another organism can already control humans. Have you considered intra-terrestrials?

The bacteria that live in us — and on us — already influence us. Microbes, namely bacteria and fungi, outnumber the cells in our body by more than 100 times. This diverse community of organisms is our microbiome. The microbiome is an important source of nutrients, and it’s our first line of defense against microbes that could cause disease. Changes in the microbiome can lead to health issues, including obesity, irritable bowel syndrome, skin diseases, urogenital infections, allergies and even emotional and behavior changes.

An intriguing area of current biomedical research is exploring connections between the microbiome in our guts and the health of our brain. The adage of thinking with your gut isn’t too far off the mark. We know that communication between the microbes and the brain is bidirectional. The intestinal tract is the source of the highest concentration of nerve cells outside the brain. The immune system, nerve cells and microbes all produce small molecules that serve as messengers between the gut and the brain. These communication systems help the immune system and the gut function normally.

Changes that affect brain-gut communication can also lead to neurological disorders such as attention deficient hyperactivity disorder, depression, autism spectrum disorder and anxiety. There’s accumulating evidence that some probiotics can alter brain-gut communication and possibly treat diseases. According to the World Health Organization, probiotics are live microbes that, when ingested in appropriate levels, confer a health benefit.

A subclass of probiotics is called psychobiotics, and they can affect cognitive function. Recent studies suggest that certain bacteria can reduce anti-inflammatory effects in the brain and make the brain more resistant to stress. In animal studies, the bacterium Mycobacterium vaccae, reduced anti-inflammatory activity in the brain. This is important because inflammatory responses are associated with mood disorders such as anxiety and depression.

Researchers have shown that giving this bacterium to rats leads to higher levels of an anti-inflammatory molecule called interleukin-4 in an area of the brain called the hippocampus. The hippocampus is the region of the brain that controls cognitive function, anxiety and fear. Also, animals treated with the bacteria had higher levels of proteins that reduced inflammation in the brain. This was linked to treated animals exhibiting lower levels of stress.

If similar effects are seen in people, this bacterium could be used as a probiotic to treat soldiers for post-traumatic stress disorder or immunize those in stressful jobs from stress-related disorders.

We’re only beginning to understand the many effects of our relationship with our microbiome — these microbes we live with. Sometimes it does make you wonder if we only assume we’re in control of ourselves, or if we share this with our microbial friends.

Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at

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