Microtubules are found in all eukaryotic cells. Even single celled organisms. If microtubules are responsible for cognition, what are brains for, and why aren’t amoeba intelligent?
Have you ever watched an amoeba do its thing? I wouldn't call it cognition, but its behavior is remarkable for something with no neurons. In fact microtubules are the exact structure posited to be responsible for where and how amoebas move their pseudopods.