University College London researchers review the primary physiological mechanisms by which microbes in the gut can influence the human brain and psychological states.
In the article’s highlights in the Journal of Psychiatric Research, they write that, “Gut microbes are part of the unconscious system influencing behavior; Microbes majorly impact on cognitive function and fundamental behavior patterns; Disorganisation of the gut microbiota can negatively impact on mental health; Psychobiotics are probiotics with a potential mental health benefit.”
They cover nine main means by which microbes can effect psychological changes in humans, including key communication routes, neurotransmission, and brain derived neurotrophic factor levels.
Dinan, Timothy G., Roman M. Stilling, Catherine Stanton, and John F. Cryan. “Collective Unconscious: How Gut Microbes Shape Human Behavior.” Journal of Psychiatric Research 63 (April 1, 2015): 1–9. doi:10.1016/j.jpsychires.2015.02.021. (Full text)