The Human Brain Is Actually Two Separate Organs, Stanford Study Finds

New research led by Stanford Medicine has upended a long-standing assumption about the brain, revealing that it is not a single, unified organ but two distinct ones that evolved independently over hundreds of millions of years.Published Friday in “Nature Neuroscience,” the study challenges the decades-old theory that a single progenitor cell gives rise to the entire brain. Instead, researchers found that the human brain is made up of two ancient nervous systems packaged together — a primitive system that governs automatic functions like heartbeat and breathing, and a more advanced one responsible for language, reasoning, and abstract thought.“We’ve shown for the first time that the front of the brain arises from a totally different progenitor cell than the back of the brain,” said an associate professor of developmental biology and the study’s senior author, Kyle Loh, in a Stanford Medicine press release. “Our discovery means that we can now grow neurons from the back of the brain, the hindbrain, in a petri dish and study their functions.”Graduate students Carolyn Dundes and Rayyan Jokhai, co-first authors of the study, made the discovery while examining mouse embryos during gastrulation, the earliest stage of embryonic development. They identified two separate progenitor cells: one, marked by a gene called Otx2, that forms the forebrain and midbrain, and another, marked by Gbx2, that exclusively forms the hindbrain. The two cell populations never overlap.The team also found that these cells package their DNA differently from the earliest stages, effectively locking each into its developmental fate. That finding may explain why scientists have struggled for decades to grow hindbrain neurons in the lab.“Previous attempts to make hindbrain neurons likely tried to coax forebrain and midbrain progenitors into hindbrain cells, which our study shows is not possible,” Mr. Jokhai said in the release.Using this insight, the researchers successfully grew functional human hindbrain motor neurons from stem cells for the first time. That breakthrough could open new doors for studying spinal muscular atrophy and amyotrophic lateral sclerosis, both of which damage hindbrain neurons that control swallowing and breathing.The team also traced the two-origin brain pattern back more than 550 million years, finding similar patterns in chickens, zebrafish, and acorn worms.“I was surprised at our findings because the word ‘brain’ implies a contiguous organ that likely has a singular origin,” Mr. Jokhai said. “But even 500 million years ago, there were these separate neural systems, which now almost operate as one, which is very cool.”

The Human Brain Is Actually Two Separate Organs, Stanford Study Finds

The Human Brain Is Actually Two Separate Organs, Stanford Study Finds

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