With all the hormones and whatnot inside. Dopamine, adrenaline, melatonin, whatever. Also, there's this Hunter S. Thompson bit on the.. pineal gland?
If it had an effect on you, wouldn't it be a really messed up high, all over the place? With uppers, downers etc mixed? (Not including the emotional implications of eating raw human brains.)
As far as the pineal gland goes, a book written in 2000 (DMT: The Spirit Molecule) declares the pineal gland produces enough DMT (Dimethyltryptamine) to experience hallucinogenic effects but this has not been confirmed, trace amounts of DMT has been found in the pineal glands of rats, but not humans.
If there was enough DMT in a pineal gland and you ate it, you would also need to inhibit certain enzymes that break it down, namely, Monoamine Oxidase.
i bet a lot of people know more than you due to the question that you asked being very far off base from how anything actually works
brain when consumed digests so if any chemicals were still there theyd have been metabolized into something different including dmt probably but im not sure if dmt is bioavailable in the stomach