Lab-grown human brain tissue connected with the nervous systems of mice engineered to lack most of their cerebral cortex and hippocampus, according to a post describing a Stanford study. The account says mice with grafts performed above chance on a Y-shaped maze test associated with working memory, while mice without grafts did not. It cautions that this does not establish that memories were stored in the human cells. NPR describes the mice as a disease-research tool and reports ethical questions about whether their treatment should change.