The Human Brain Turned Out to Be Two Separate Organs

Summary

A study by Stanford developmental biologists, published in Nature Neuroscience, challenges the traditional view that the brain develops from one uniform population of neural stem cells. It suggests that the brain’s major regions arise from two distinct neural cell lineages that develop alongside one another and later work together:

• Anterior neural ectoderm (ANE): Expresses the gene OTX2 and gives rise to the forebrain and midbrain, associated with functions such as conscious thought, language, and complex reasoning.
• Posterior neural ectoderm (PNE): Expresses GBX2 and gives rise to the hindbrain, including the brain stem, which helps regulate automatic functions such as breathing, heart rate, sleep, and swallowing.

The researchers report that the lineages remain distinct early in development. Their experiments also suggest that cells from one lineage resist signals intended to make them adopt the other lineage’s identity. The findings may explain why earlier attempts to produce hindbrain motor neurons from stem cells often instead produced forebrain- or midbrain-like cells.

Methods and findings

• Fluorescent lineage tracing: Researchers labeled cells with glowing proteins to follow their descendants. The labeled ANE and PNE populations developed into different brain regions.
• Epigenetic analysis: Researchers examined which genes were accessible and active in each cell population, finding patterns associated with their respective developmental paths.
• Cell-identity experiments: Progenitor cells were exposed to chemical signals intended to redirect their fate. The cells largely retained their original identities.
• Lab-grown hindbrain neurons: By selecting the appropriate progenitors and chemical conditions, researchers produced functional hindbrain neurons that showed spontaneous electrical activity and expressed genes linked to facial movement and swallowing.
• Comparisons across species: The video describes similar use of the developmental genes Otx2 and Gbx2 in animals including chickens, zebrafish, and worms. It presents this shared arrangement as evidence that the two-part developmental blueprint may be hundreds of millions of years old.

Other neuroscience findings discussed

• An NIH BRAIN Initiative cell atlas, based on RNA sequencing, identifies at least 3,000 types of brain cells, rather than the handful often presented in basic textbooks.
• Human accelerated regions (HARs) are described as non-coding DNA regions that may affect development by extending the period of neural stem-cell growth, helping explain the human brain’s size and complexity.
• The brain is described as an energy-intensive organ, accounting for a substantial share of the body’s blood flow, oxygen use, and glucose consumption.

The proposed developmental distinction could aid research into disorders that affect particular neural populations, including ALS. It may help researchers generate relevant motor neurons from a patient’s cells for laboratory studies. The findings could also support research into hindbrain circuits involved in hunger and metabolic regulation, including circuits targeted by GLP-1 medications such as semaglutide.

Researchers and sources featured

• Stanford developmental biologists: The researchers behind the study; individual names are not given in the subtitles.
• The study published in Nature Neuroscience: The primary research source described.
• NIH BRAIN Initiative cell atlas: The source associated with the RNA-sequencing survey of brain cell types.
• Research on human accelerated regions (HARs): Discussed as a source of evidence about human brain development; no specific researchers or publication are named.
• Comparative brain-development research: Research involving chickens, zebrafish, worms, and jellyfish is described in the video; no individual researchers or publications are identified.