Dr. Kirsten Tillisch, an associate professor of medicine at UCLA's David Geffen School of Medicine in Los Angeles, said the small study involved 36 women ages 18-55.
The researchers divided the women into three groups: one group ate a specific yogurt containing a mix of several probiotics -- bacteria thought to have a positive effect on the intestines -- twice a day for four weeks; another group consumed a dairy product that looked and tasted like the yogurt but contained no probiotics; and a third group ate no product at all.
Functional magnetic resonance imaging scans conducted both before and after the four-week study period looked at the women's brains in a state of rest and in response to an emotion-recognition task in which they viewed a series of pictures of people with angry or frightened faces and matched them to other faces showing the same emotions.
This task, designed to measure the engagement of affective and cognitive brain regions in response to a visual stimulus, was chosen because previous research in animals had linked changes in gut flora to changes in affective behaviors.
The study, to be published in the journal Gastroenterology, said signals were sent from the intestine to the brain. That they could be modulated by a dietary change might lead to an expansion of research aimed at finding new strategies to prevent or treat digestive, mental and neurological disorders, the study said.