Human brain is two separate organs, Stanford Medicine-led research finds
Human brain is two separate organs, Stanford Medicine-led research finds. Tryfonov/Adobe Stock News Neurobiology September 18, 2026 Human brain is two separate organs, Stanford Medicine-led research finds By Krista Conger A new study led by Stanford Medicine found the brain is two separate organs adjacent to one another.
What happened
Skip to main content Skip to section navigation Stanford Medicine researchers have shown that the human brain is two distinct organs, a finding that creates opportunities for studying devastating diseases that affect one of those parts — the brain stem. But new research led by Stanford Medicine reveals that what we call the brain is two distinct organs that evolved independently over hundreds of millions of years. This work was supported by the National Institutes of Health (grants DP5OD024558, DP2GM146258, R00GM121852, R01DK115728, R01DE027538, T32GM119995, T32GM007365, T32GM007790 and F31DE031154); the National Science Foundation; the California Institute for Regenerative Medicine; the Spinal Muscular Atrophy Foundation; a Stanford Maternal and Child Health Research Institute grant; the Stanford Beckman and Ludwig Centers; the Siebel Stem Cell Institute; a Stinehart-Reed Foundation grant; the Gatsby Charitable Foundation; the Howard Hughes Medical Institute; the Packard Foundation; the Pew Charitable Trusts; the Baxter Foundation; the Human Frontier Science Program; and the anonymous, Fickel, Gilbert, and Stinehart-Reed families.
Image source, S Pasca/StanfordImage caption, In scans of the implanted mice, researchers were able to see connections between the human brain cells and the rest of the mouse brainThe aim of this ethically complicated breakthrough was to better understand the biology of brain disorders for which there are currently no effective treatments. The new research finding shows that the human brain consists of two ancient nervous systems cleverly packaged together — a more primitive part that regulates our hearts’ beating, our breathing and other functions, and another that makes us distinctly human, capable of poetry, mathematics and wondering about our own origins.
Our careful attention to that early time point allowed us to find this fundamental split in brain development. ” Growing hindbrain neurons Armed with this knowledge, the researchers for the first time successfully coaxed human pluripotent stem cells (a kind of cell that can create any cell in the human body) to become functional hindbrain motor neurons in the laboratory. “But even 500 million years ago, there were these separate neural systems, which now almost operate as one, which is very cool. ” The research also has implications for investigating treatments for SMA, ALS and other conditions affecting the brain stem.
The wider picture
Image source, Getty ImagesImage caption, The research has raised questions about what it means to alter the way laboratory animals think and feel ByVictoria Gill, Science correspondent and Kate Stephens, Senior science journalistPublished16 September 2026Neuroscientists in the US have successfully adapted mice to have functioning human cells inside their own brains. The researchers then used skin cells taken from humans and "reprogrammed" them, so they grew into pieces of brain-like tissue. Dr Sarah Chan, a reader in bioethics at the University of Edinburgh who was not involved in this research, told BBC News there was "no indication that what's being created here are mice that can think like humans, or a human brain in a mouse body.
For decades researchers have subscribed to the theory that there is a single progenitor cell early in development that gives rise to the entire brain. Despite the critical importance of the hindbrain, scientists have struggled for decades to generate human hindbrain neurons in the laboratory. This gap has hampered research into devastating diseases affecting the brain stem, including spinal muscular atrophy and amyotrophic lateral sclerosis. Jokhai and Dundes discovered that the hindbrain follows a separate developmental path, running in parallel to — rather than branching off from — the pathway that creates the forebrain and midbrain.
They found the same two-origin brain pattern in chickens; zebrafish; and, remarkably, in acorn worms, tiny creatures living on the ocean floor that share a distant common ancestor with humans.
What has been reported
“Having the brain as one organ would probably be more efficient, but we rely on this primordial way to make the brain as two separate pieces. ” “I was surprised at our findings because the word ‘brain’ implies a contiguous organ that likely has a singular origin,” Jokhai said. The researchers would like to extend their studies to determine the developmental origins of the spinal cord and to learn exactly how SMA and ALS compromise the function of hindbrain neurons.
“This is a very exciting new frontier in brain research. ” Researchers from the California Institute of Technology and the University of California, San Francisco contributed to the study. About Stanford Medicine Stanford Medicine is an integrated academic health system comprising the Stanford School of Medicine and adult and pediatric health care delivery systems. Together, they harness the full potential of biomedicine through collaborative research, education and clinical care for patients. After completing the science writing program at UC Santa Cruz, she joined the Stanford Medicine Office of Communications in 2000.
In her spare time, she enjoys textile arts, experimenting with new recipes and hiking in beautiful northwestern Montana, where she was raised and now lives. kristac@stanford. edu Media Contact Krista Conger Tel 650-725-5371 kristac@stanford. edu Related Related Articles Neurology & Neurosurgery September 08, 2023 Scientists identify 'Velcro-like' molecule to potentially treat ALS A drug created by Stanford Medicine scientists aimed at a 'Velcro'-like protein reduces ALS symptoms and improves survival in mice. Neurology & Neurosurgery January 18, 2022 Discovery of hundreds of genes potentially associated with ALS may steer scientists toward treatments Using machine learning, Stanford Medicine scientists and their colleagues have found hundreds of genes that could play a role in amyotrophic lateral sclerosis.
What happens next
The researchers hope that potential treatments for psychiatric and neurodevelopmental diseases that only occur in humans could now be tested on the laboratory rodents. While mice with brains that are partly human might sound like a Kafkaesque experiment, the scientists said these are not "mice that think like humans". The animals are genetically engineered – and surgically altered – so that some of their brain tissue is human. As lead researcher Prof Sergiu Pașca from Stanford University explained in a press conference, psychiatry has "one of the lowest success rates for clinical trials".
"The Stanford researchers said that, for some complex conditions, including epilepsy, autism and cerebral palsy, it has the potential to be "transformative". Pașca said: "Here we have a new model that allows us to actually capture aspects of human brain function in a way that has not been possible before. "Image source, Luis AlvarezImage caption, The hope is that this will provide a new way to investigate the biology of some human brain disordersMice without their 'grey matter'The human brain is made up of billions of cells, interconnected in millions of circuits, making it difficult to understand its development and what exactly is happening – at the cellular level – when things go wrong.
The report has been compiled by Press Orb using information reported across med.stanford.edu, bbc.co.uk. Details are presented according to the information available at the time of publication and may change as authorities, organisers or other relevant parties provide updates.