Not an expert so you can disregard every word I say.

Answer to your question depends on functions provided by gut microbes. We can say it's to digest the food and it's symbiotic relationship. But what if this is what we know only on the surface. What if these microbes produce proteins that are absolutely essential for many other functions as well. What if they signal messages that are of neural nature.

It's a pitfall to think that our brain is all we are as it hosts consciousness. I held this view for a long time, so I understand where it's coming from.

But try changing your diet. I won't make any suggestions but there are limitless option to biohack your body. You will see amazing effects on your brain too.

Btw, there's a neural setup i.e a brain in stomach and heart as well.