Human brain is two separate organs, Stanford study reveals after 550 million years

A Stanford Medicine-led study has challenged the idea that the human brain developed as one organ. Researchers found that its front and back sections come from two separate early cell groups, a discovery that could change research into ALS, spinal muscular atrophy and other neurological diseases.

In Short

• Stanford researchers found that the front and back of the human brain have different origins
• The two-part pattern dates back more than 550 million years in evolution, researchers found
• Scientists grew human hindbrain nerve cells in a lab, opening new possibilities for disease research

For centuries, the human brain has been treated as one organ. A new Stanford Medicine study has now challenged that basic idea.

Researchers found that the front and back parts of the brain develop from two different groups of early cells. Their work suggests these were once separate nervous systems that evolution eventually brought together.

The finding could also explain why scientists have struggled for years to grow certain brain cells in laboratories.

TWO SYSTEMS, ONE BRAIN

The brain's front section is involved in language, consciousness, reasoning and other abilities that make humans distinctive.

The hindbrain, at the back, handles jobs we rarely think about but cannot live without. It helps control breathing, heartbeat, sleep, hunger, swallowing and movements of the face and throat.

Stanford researchers found that these two regions do not start from the same early cell group during development.

They identified two separate groups in developing mouse embryos. One eventually formed the forebrain and midbrain, while the other became the hindbrain. The two groups remained separate from the earliest stages.

According to the researchers, this could explain decades of difficulty in producing human hindbrain nerve cells in the laboratory. Scientists had been trying to turn one type of early cell into another that it could not naturally become.

THE DISCOVERY GOES BACK 550 MILLION YEARS

The researchers then looked beyond mice and humans.

They found evidence of the same two-origin pattern in animals including chickens and zebrafish. They also found it in acorn worms, tiny ocean animals that share a distant ancestor with humans.

That suggests the split is not a recent feature of the human brain. It may have existed for more than 550 million years.

"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," Stanford's Kyle Loh said.

WHY THIS COULD MATTER FOR ALS AND SMA

The discovery is more than a new way of looking at the brain.

Using what they learned, the researchers successfully produced functional human hindbrain motor neurons from stem cells in the laboratory. These cells showed characteristics of real hindbrain cells, including activity linked to facial and swallowing muscles.

That could give scientists a new way to study conditions such as spinal muscular atrophy and ALS, which damage nerve cells involved in movement, swallowing and breathing.

The researchers say the work could eventually help them better understand what goes wrong in these diseases and explore possible treatments.

The study was published in Nature Neuroscience on September 18.

- Ends