We Aren’t Born With A Finite Number Of Brain Cells

By Debra Kelly on Saturday, April 5, 2014
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“Brain, n. An apparatus with which we think we think.” —Ambrose Bierce, The Devil’s Dictionary

In A Nutshell

It’s long been thought that humans are born with all the brain cells that we’ll ever have. Some researchers have been fighting that theory for decades and were met with extreme resistance—one even was forced to give up a research career in disgrace. But it turns out that he was right. A process called neurogenesis has been proven to occur in the brains of first rats, then other large mammals, then in humans.

The Whole Bushel

For as long as we’ve been aware of how neurons in the brain work, we’ve thought that the neurons you were born with were all that you got. That was one reason why we kept getting lectures from our parents on why we shouldn’t be rotting away our brains with all those video games and mindless television, after all. We had a finite number of brain cells, and what’s more valuable than brain cells?

Only it turns out, that’s not true at all. People are constantly developing new neurons in a process called neurogenesis, even well into adulthood. The theory was first put forth in 1962 by a scientist named Joseph Altman, but the papers he published were outright ignored by the medical community. A decade later, two other researchers took up the theory. Fernando Nottebohm started his research on birds, while Michael Kaplan worked with the brains of rats.

When Kaplan published his work, it destroyed his career as a researcher. Not only did no one publicly support his work, they criticized it to the point where he saw little choice but to abandon not only the theory but all his future work as a researcher. He went on to work as a rehabilitation doctor, and it wouldn’t be until decades later that further research would show that he was right all along.

Neurogenesis was first accepted as happening in birds and later in primates, but even those researchers that admitted this were hesitant to believe that it was happening in more complex human brains.

However, now we know exactly where new brain cells are born and how they get from one area of the brain to another. And it was a scientific discovery that hinged on thinking outside of the box.

Researchers from the University of Auckland were looking for pathways that they knew had to be there; new, young brain cells had been found in the subventricular zone, but they couldn’t stay there. There needed to be a way for the new cells to travel from one area of the brain to another, but they just couldn’t find it.

As had always been done, they were examining thin slices of brain tissue that had been cut from the front to the back of the brain, giving a side-view cross-section to them to examine. In some sections, they saw something that could work… in others, there just was nothing.

So they flipped the brain around, and took a cross-section of it cut differently, as though they were looking at it from the front.

In that cross-section, they were able to confirm that there was, indeed, a place where new brain cells were born and pathways for them to travel. Not all areas of the brain have been found to be fed new brain cells, but ones that are include the hippocampi, which is responsible for navigation and direction.

That’s evidence that’s supported by a study of the brains of London’s famous black cab drivers. Cab drivers, who need to pass grueling tests and know an excruciating amount of information before they’re allowed to legally drive one of the city’s trademark black cabs, tend to have abnormally large hippocampi as determined by imaging scans of their brains. This suggests that in order to remember and process all the directional information they need to access on a daily basis, their brains are feeding them new brain cells to do so.

This would point to the fact that there’s something to those lectures after all. The more a brain works and the more that it’s challenged, research shows that the more neurons will be formed.

Show Me The Proof

NPR: Researchers Map Path of Humans’ New Brain Cells
Neurogenesis: A Brief History and Timeline
BBC News: Taxi drivers’ brains ‘grow’ on the job
Psychology Today: How to Grow New Neurons in Your Brain