"Brain" is just a stand-in for any system which can correlate its state with another system.

Whomst do you think performs the experiments?

Just for your information: Contrary to how it may appear in internet memes, "whomst" isn't really a standard English word.

https://en.m.wiktionary.org/wiki/whomst

Give it some time. Few years ago you wouldn't be able to legally google it in English

Well, like I said - it doesn't matter.