Hi all,
I just happened to see this recent post and thought I'd recommend an article posted in the latest, Sept 2012, Monitor on Psychology magazine titled, "That Gut Feeling" by Dr. Siri Carpenter (pg. 50).
The article basically explains studies, mostly rats, that show it's a two-way street; the whole brain-gut dynamic. Meaning psychological upset can cause gut upset, just as much as gut upset can cause psychological upset via the "vagus" nerve which somehow connects gut microbiota populations(probiotics) to neurochemical responses resulting in depression/stress/anxiety.
The article detailed a few studies in which varying stress responses were shown to be reversed, or caused, by the introduction, or wiping-out, of specific probiotic strains. Of particular note were: Bifido Infantis, Lactobacillus Rhamnosus, Bifido Longum, and Lactobacillus Helveticus.
There werethree studies involving humans which showed promise. A study of college students observed diminished lactobacilli populations when comparing samples from the first few days of school to exam week. British Journal of Nutrition in 2011 found that "a 30-day course of probiotic bacteria (l. helveticus, b. longum) led to decreased anxiety and depression in health human volunteers." An as-of-yet unpublished neuroimaging study, examining the effects of probiotics on brain activity, revealed an "observable" effect on brain activities while they viewed either neutral or negative emotional stimuli.
I would definitely give such things due consideration. Whether or not you or your loved one has noticed digestive effects from various brands of probiotics should perhaps consider the mental states as well. That being said, different brands vary in quality and effectiveness greatly. Also, certain formulations may only be helpful for certain segments of the digestive tract--just my unqualified opinions.