The human brain is not a single organ, but two separate systems that evolved independently before fusing together, according to groundbreaking new research. … Armed with the knowledge of how hindbrain cells uniquely form, the team has successfully turned human stem cells into becoming functional hindbrain motor neurons in a lab for the first time.
To expand on what frongt said. An organ is a collection of specialized tissues that performs certain specific tasks. The stomach is an organ, the pancreus is an organ, and together they are part of a system. If the brain is more than one organ, we can target specific parts in the tissue differences for lab cell growth (as the article suggests), targeted medicine delivery (due to differences in autonomic braincell makup vs frontal and temporal processing tissues), and the next step in research will probably be how the two brain organs develop connections which could lead to nerve pathway repair (typically very hard to achieve).