Stanford Scientists Uncover Evidence Human Brain Is Made of Two Distinct Parts - Video

A new Stanford Medicine study suggests that the human brain may have evolved from two separate nervous systems rather than developing as one continuous structure.

Published in Nature Neuroscience, the study found that the front and back regions of the brain arise from different groups of early cells during development. The finding may help explain brain evolution and difficulties producing some nerve cells in the laboratory.

Researchers studied developing mouse embryos and identified two distinct groups of early progenitor cells. One group eventually formed the forebrain and midbrain, regions involved in functions such as reasoning, language and consciousness. The other formed the hindbrain, which controls essential functions including breathing, heartbeat, swallowing, sleep and facial movements.

The researchers found evidence of the same developmental pattern in chickens and zebrafish. They also observed it in acorn worms, suggesting that the two-origin arrangement may have existed for more than 550 million years, rather than being a recent feature of the human brain.

The discovery also helped address a long-standing laboratory challenge. Using information about the different developmental origins, the researchers successfully produced functional human hindbrain motor neurons from stem cells. The cells displayed characteristics of hindbrain neurons and showed activity associated with muscles involved in facial movement and swallowing.

These findings could provide a new laboratory model for studying neurological disorders that damage motor neurons, including spinal muscular atrophy and amyotrophic lateral sclerosis (ALS). Such cells may help researchers study how these diseases affect movement, swallowing and breathing and support potential future treatment research in motor neuron disorders.

However, the findings are primarily developmental and laboratory-based. Laboratory-produced nerve cells are not currently a treatment.

Further research will be needed to determine whether these cells accurately model human disease or contribute to future therapies.

REFERENCE: Jokhai, R.T., Dundes, C.E., Ahsan, H.S. et al. Two parallel neural ectoderm progenitors contribute to the developing brain. Nat Neurosci (2026). https://doi.org/10.1038/s41593-026-02433-7