I wouldn't be surprised if we see more connections between the gut-brain revolving around the vagus nerve. It joins the brain suspiciously close to areas like the hippocampus and the substantia nigra where we see dementia and parkinson's start.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6170613/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5440238/