Circular reasoning and begging the question. We don't actually know what brain tissue does and have no way to find out, currently.

Au contraire, there is plenty of findings as to what neurons and clumps of neurons do.

Begging the question again, as there is no evidence that "intelligence" runs on neurons. (And plenty of evidence that "intelligence" can exist without neurons.)

What evidence is there that intelligence can exist without neurons?

Single-celled organisms are pretty intelligent, and they have zero neurons. Meanwhile there is no evidence at all that intelligence runs on neurons except that "brains contain lots of neurons", which is a logical fallacy because brains contain lots of other spurious things too.