Human brain organoids transplanted into rats could be used as an in vivo model for the study of neuropsychiatric diseases. Researchers at Stanford University managed to mature human organoid neurons in the somatosensory cortex of the animal's brain and incorporate them into its neural circuitry.The integration improved the morphological and physiological properties of the transplanted neurons. Compared to those of organoids in a Petri dish, human cells preserved their own identity, and they modified the rat's learned behavior through stimulation and reward experiments.