Here are some links that I and others have found useful.
CAUSES and TREATMENT:
Gut Bacteria Might Guide The Workings Of Our Minds
Chronic Stress Changes Immune Cell Genes, Leading To Inflammation
Recycling Metchnikoff: probiotics, the intestinal microbiome and the quest for long life
Thesis: ‘ADHD, a Food-Induced Hypersensitivity Syndrome’
New Research shows Leaky Gut Is Real
Image credit (cropped): Masahiro Ihara