The brain is probably the least explored organ, much of which is due to the difficulty of studying it in situ rather than in slices under a microscope. Even growing small organoids out of neurons provide few clues, as this is not how brain tissue is normally organized. A possible breakthrough may have been found here by a group of researchers whose article in Cell Stem Cell details how they created functional human neural tissues using a commercial 3D bioprinter.
This is a companion discussion topic for the original entry at https://hackaday.com/2024/02/12/3d-printing-functional-human-brain-tissue-for-research-purposes/