A team of scientists at the Institute of Molecular Biotechnology in Austria have developed a method for growing human brain tissue from stem cells. The immature brain cells can self-organize into three-dimensional structures similar to that in the developing brain. The "cerebral organoids" are approximately four millimeters across and have distinct sections, and according to senior report author Juergen Knoblich, the "proto-brain resembles the developmental stage of a nine-week-old fetus’s brain."
The tiny organs contain sections of the cortex, hippocampus and retinas although "one brain region that wasn't present was the cerebellum, the part of the brain that handles motor skills and language, among other functions. This isn't surprising, says [Madeline Lancaster, another scientist at the Institute], since this region develops later than the others."
Though it does not mean the brain is actually conscious, scientists were able to detect neurons firing in the small pieces of gray matter. That activity, via a video from New Scientist, can be seen below.