Our brain keeps making new neurons - even in old age

For a long time, people believed the brain stops making new neurons after childhood. Scientists repeated this idea in books and lectures for years. They thought the brain had a deadline for growth, but they were wrong.

A new study has flipped this idea. Researchers from Karolinska Institutet in Sweden found clear proof that the brain keeps making neurons well into old age.

This discovery changes everything. It suggests the brain stays flexible for much longer than we thought. And it brings hope for new treatments for brain disorders.

Adults grow new neurons

The story begins with the hippocampus. This brain region helps you learn, remember, and handle emotions. It is always busy.

In 2013, Jonas Frisén and his team showed something surprising. Adults can grow new neurons in their hippocampus. They proved it by measuring carbon-14 in DNA from brain tissue.

This method showed exactly when neurons were born. Suddenly, the old belief about brain growth began to crumble.

Still, many scientists remained doubtful. They asked whether the brain really keeps growing neurons throughout life.

Origin of new neurons in the brain

The biggest question focused on neural progenitor cells. These early cells later become neurons. Do they still exist and divide in adult brains? This new study answered that clearly.

“We have now been able to identify these cells of origin, which confirms that there is an ongoing formation of neurons in the hippocampus of the adult brain,” said Jonas Frisén.

The experts looked at brain tissue from people of all ages. They studied brains from newborns to people in their late seventies.

The researchers used a tool called single-nucleus RNA sequencing. This allowed them to read gene activity inside each brain cell nucleus. They also used flow cytometry, which looks at the properties of cells.

Neurons keep growing in adult brains

With help from machine learning, the experts connected the dots. They traced the full process of neuron growth, starting with stem cells and ending with young neurons. Many of these cells were still dividing.

By mapping the process, the team revealed the full journey of neuron growth in the brain. They watched cells change step by step, from stem cells to fresh neurons.

The results left no doubt. Neurons do not just grow in childhood. The brain keeps producing them far into adulthood.

Some adults had many cells ready to become neurons, while others had fewer. The differences were clear.

Birthplace of new neurons

The researchers wanted to see where the new neurons were forming. They used RNAscope and Xenium to find out. These tools showed exactly where genes switched on during neuron growth.

The new neurons appeared inside a brain region called the dentate gyrus. This area sits inside the hippocampus. It plays a key role in memory, learning, and flexible thinking.

This finding shows the adult brain still has hidden pockets of growth.

Neuron growth in humans and animals

The experts also found some interesting connections. Neuron-making cells in humans look quite similar to those in mice, pigs, and monkeys. But they are not exactly the same.

Some genes behave differently in humans. This shows humans have their own special brain features.

The team also noticed something else. Some people had many neural progenitor cells, while others had very few.

“This gives us an important piece of the puzzle in understanding how the human brain works and changes during life,” explained Frisén.

“Our research may also have implications for the development of regenerative treatments that stimulate neurogenesis in neurodegenerative and psychiatric disorders.”

What this means for the future

This discovery opens a new chapter in brain science. It proves the brain is not as fixed as we once believed.

New neurons keep forming throughout life. The process does not stop after childhood, and now we know exactly where this happens and which cells drive it.

This knowledge could lead to treatments for memory loss and mental health conditions. It might even help repair brain injuries.

The human brain, with its billions of neurons, is more surprising and powerful than anyone imagined. And it still has secrets left to share.

Frisén collaborated with Ionut Dumitru, Marta Paterlini, and others at Karolinska Institutet. Researchers from Chalmers University of Technology in Sweden also contributed.

The project received support from several organizations, including the Swedish Research Council and the Knut and Alice Wallenberg Foundation.

The study is published in the journal Science.

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