In 1994 I was diagnosed with celiac disease, which led me to create Celiac.com in 1995. I created this site for a single purpose: To help as many people as possible with celiac disease get diagnosed and living happy, healthy gluten-free lives. Celiac.com was the first site on the Internet dedicated solely to celiac disease, and since then it has become an invaluable resource to people worldwide who seek information about celiac disease and the gluten-free diet. (snip. The articles goes on to explain that these peptides are biologically active & somewhat similar to opioid peptides.)
It is well known that casein (from human or cows milk) will break down in the stomach to produce a peptide known as casomorphine, which, as the name implies, will have opioid activities. Similar effects are noted with gluten from wheat and some other cereals ...in which the compounds formed are gluteomorphins (or gliadinomorphins).
So some of us who are gluten sensitive are also casein sensitive, and a gluten ingestion will affect brain activity.