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 so they can begin to live happy, healthy gluten-free lives. Celiac.com was the first site on the Internet dedicated solely to celiac disease. In 1998 I founded The Gluten-Free Mall, Your Special Diet Superstore!, and I am the co-author of the book Cereal Killers, and founder and publisher of Journal of Gluten Sensitivity.
Proteins consist of long chains of units known as amino acids. Normal proteins are digested by enzymes in the intestines and are broken down into these units. However, if for some reason this digestion is incomplete, short chains of these amino acids (known as peptides) will result. ....... The majority of these peptides will be dumped in the urine, (but) a small portion will cross into the brain and interfere with transmission in such a way that normal (brain) activity is altered or disrupted.....
(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.