Does free will exist? Follow your gut on this one. An article in Scientific American reports that bacteria in the gut may influence brain development and behavior:
this new study is the first to extensively evaluate the influence of gut bacteria on the biochemistry and development of the brain. The scientists raised mice lacking normal gut microflora, then compared their behavior, brain chemistry and brain development to mice having normal gut bacteria. The microbe-free animals were more active and, in specific behavioral tests, were less anxious than microbe-colonized mice. In one test of anxiety, animals were given the choice of staying in the relative safety of a dark box, or of venturing into a lighted box. Bacteria-free animals spent significantly more time in the light box than their bacterially colonized littermates. Similarly, in another test of anxiety, animals were given the choice of venturing out on an elevated and unprotected bar to explore their environment, or remain in the relative safety of a similar bar protected by enclosing walls. Once again, the microbe-free animals proved themselves bolder than their colonized kin.
When Pettersson’s team performed a comprehensive gene expression analysis of five different brain regions, they found nearly 40 genes that were affected by the presence of gut bacteria. Not only were these primitive microbes able to influence signaling between nerve cells while sequestered far away in the gut, they had the astonishing ability to influence whether brain cells turn on or off specific genes.
The article also runs down some other findings on the possible influence of gut bacteria on our health and behavior:
these bacteria have been implicated in the development of neurological and behavioral disorders. For example, gut bacteria may have an influence on the body’s use of vitamin B6, which in turn has profound effects on the health of nerve and muscle cells. They modulate immune tolerance and, because of this, they may have an influence on autoimmune diseases, such as multiple sclerosis. They have been shown to influence anxiety-related behavior, although there is controversy regarding whether gut bacteria exacerbate or ameliorate stress related anxiety responses. In autism and other pervasive developmental disorders, there are reports that the specific bacterial species present in the gut are altered and that gastrointestinal problems exacerbate behavioral symptoms. A newly developed biochemical test for autism is based, in part, upon the end products of bacterial metabolism.
There are a bunch of links in that paragraph in the original article. Read the whole thing here and don’t fault me for recycling the joke the author uses to lead into the article—the Bifidobacteria made me do it.