The extraordinary gene that made our brain special

Neurons are generated by neural stem cells

Why are we the way we are? What makes each of us unique in the world?
The answer is, without a doubt, in our brain. And more particularly, in the cerebral cortex, its largest and most complex part. As its name suggests, it covers the brain and gives it its typical rough appearance.

The cerebral cortex of the human being is one of the greatest wonders of nature, which has allowed us to go from using the simplest tools of our ancestors to creating tools as complex as a laptop or an international space station. Thanks to the cerebral cortex we can build from the largest and most efficient buildings to the most beautiful cathedrals.

We can have highly subtle social interactions and be able to identify a new type of virus such as SARS-CoV-2 in record time and develop an effective vaccine against it.

Furthermore, in the cerebral cortex resides much of what makes each one of us unique: our personality.

How did our cerebral cortex evolve?

Like our hands and our nose, our cerebral cortex is the product of millions of years of evolution.
After the great extinction of the dinosaurs 66 million years ago, the largest surviving mammals were not much larger than a vole, and their cerebral cortex weighed a few grams. However, the incessant action of multiple factors continued to create mutations in the genome of these primitive mammals, just as it had been happening since the origin of life.

Some of these mutations were harmful (such as those that cause skin cancer, for example), and were lost when their carriers perished. But other genetic mutations were beneficial, and carried over into subsequent generations.

Through this process repeated over millions of generations, the small and relatively simple cerebral cortex of those early mammals increased in size and complexity until it became the phenomenal organ that occupies our skulls today and allows us to understand this article.

Well, the study that we have carried out from the Institute of Neurosciences in Alicante has discovered one of these genetic changes that took place during evolution and that were key to the expansion of the human cerebral cortex.

The cortex is formed during embryonic development from neural stem cells, which constantly divide, giving rise to two daughter cells after each division. Early in development, the division of neural stem cells generates more stem cells, thus increasing in number.

From a certain moment, these begin to generate neurons (neurogenesis), which will finally make up the adult cerebral cortex.

This is a critical step, because when cell division produces two neurons, there are no spare stem cells left to continue producing more neurons.

Therefore, the total number of neurons in the cortex depends on the number of neural stem cells that have to generate them. And the more neurons are generated and the more varied they are, the greater the size and complexity of the cerebral cortex.

In the human embryonic brain the number of neural stem cells, their diversity and their capacity for proliferation are enormous, while in the small mouse embryo they are much smaller.