Human brain cells don’t continue to grow into adulthood, according to a new study

Research with other species lends weight to these findings.

We used to think neurogenesis—the growth of new brain cells, occurred throughout one’s lifetime. A shocking new study out of UC-San Francisco finds that instead, no more memory cells grow in the hippocampus after childhood. That's staggering, as this area of the brain associated with really important things such as learning, memory, and emotion. One of the largest studies of its kind to date, the scientists examined 59 human brain specimens, all of varying ages, and found no new neuron formation past age 13.  


Neuroscientists have been debating since the late 1920s whether or not neurogenesis occurs into adulthood. From the ‘80s on, the prevailing view was that neurogenesis takes place throughout our lives. That’s because lots of studies confirmed the phenomenon occurring past the juvenile stage in the brains of other species, including birds, mice, rats, and nonhuman primates. In rats, for instance, new neurons are constantly formed around the olfactory bulb, which is associated with the sense of smell.

Arturo Alvarez-Buylla was the senior author of the study. He told Medical News Today, "We find that if neurogenesis occurs in the adult hippocampus in humans, it is an extremely rare phenomenon, raising questions about its contribution to brain repair or normal brain function." Lead researcher Shawn Sorrells, said they couldn’t find any new neurons in the adult samples they examined. The study’s findings were published in the journal Nature.

Model of the brain. By CNX OpenStax, Wikimedia Commons.

According to this research, our brain creates loads and loads of new neurons during the prenatal and neonatal stages. In early childhood, dramatic bursts of neurogenesis occur in the frontal lobe—the very front part of the brain, responsible for executive functions such as decision-making, learning, and planning. After that, neurogenesis drops off and becomes exceptionally rare, according to this study.

To conduct it, researchers collected hippocampus samples ranging from the fetal stage to age 77. These came from the US, China, and Spain. Some samples were from cadavers, while others were excess tissue removed during brain surgery, to help relieve severe epilepsy.

With each sample, the researchers examined a particular part of the hippocampus called the dentate gyrus, an area crucial to memory formation. They sliced up this region and applied antibodies which would congregate at new neurons or any newly formed cell. While this occurred often in samples from fetuses and young children, after age 1 it was rare, and after age 13, researchers found no new neuron formation.

The idea is bound to be controversial as certain diets, exercises programs, and even antidepressants, rest on the idea that they instigate the growth of fresh neurons. Among neuroscientists, there’s a variety of beliefs, ranging from the notion that the human brain generates many neurons each day, to the conjecture that neurogenesis is actually quite rare.

Neuronal formation isn’t a simple process. It begins with progenitor cells, which turn into stem cells before becoming neurons. "It requires the birth of the cell,” Alvarez-Buylla told CNN, “the migration or the movement of the cell to the right place, which is not an easy task in the very dense structure of the brain -- and then that cell has to make space to grow and connect to other cells and then contribute in a functional way to that circuit." The brains of infants and young children are primed for this, while with adult brains, researchers aren’t sure.

Neurons in an adult mouse's hippocampus. Credit: Wikipedia.

Another study that supports this one states that whales and dolphins don’t experience neurogenesis as adults. Yale neuroscientist Pasko Ravic has worked with monkeys and finds that they go through little neurogenesis during adulthood, as opposed to rodents. The reason might be, neural networks within adult primate brains are complex, and the growth of such cells could disrupt normal operations.

This study, although provocative, gives us a snapshot of only one region of the brain. More research will have to be done to confirm these results and see whether the same is true in other parts. Many neuroscientists say, even if adults do experience neurogenesis, there’s still no proof that it rejuvenates the brain. Instead, making new connections might be what’s really worthwhile. In another sense, this study could aid us in the search for a cure to Alzheimer’s, as neurogenesis was one avenue researchers were exploring.

Want to learn more about neurogenesis in the adult brain? Click here.


America’s education system is centuries old. Can we build something better?

The Lumina Foundation lays out steps for increasing access to quality post-secondary education credentials.

Sponsored by Lumina Foundation
  • America's post-high school education landscape was not created with the modern student in mind. Today, clear and flexible pathways are necessary to help individuals access education that can help them lead a better life.
  • Elizabeth Garlow explains the Lumina Foundation's strategy to create a post-secondary education system that works for all students. This includes credential recognition, affordability, a more competency-based system, and quality assurance.
  • Systemic historic factors have contributed to inequality in the education system. Lumina aims to close those gaps in educational attainment.
  • In 2019, Lumina Foundation and Big Think teamed up to create the Lumina Prize, a search to find the most innovative and scalable ideas in post-secondary education. You can see the winners of the Lumina Prize here – congratulations to PeerForward and Greater Commons!

First solar roadway in France turned out to be a 'total disaster'

French newspapers report that the trial hasn't lived up to expectations.

Image source: Charly Triballeau / AFP / Getty Images
Technology & Innovation
  • The French government initially invested in a rural solar roadway in 2016.
  • French newspapers report that the trial hasn't lived up to expectations.
  • Solar panel "paved" roadways are proving to be inefficient and too expensive.
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What was it like to live in a Japanese concentration camp?

During World War II, the U.S. incarcerated over 100,000 Japanese Americans in concentration camps throughout the West.

Universal History Archive/Universal Images Group via Getty Images
Politics & Current Affairs
  • Now that the issue of concentration camps in the U.S. has once again reared its head, it can be beneficial to recall the last time such camps were employed in the U.S.
  • After Pearl Harbor, the U.S. incarcerated over 100,000 Japanese Americans in camps, ostensibly for national security purposes.
  • In truth, the incarceration was primarily motivated by racism. What was life like in the U.S.'s concentration camps?

On February 19, 1942, President Roosevelt issued Executive Order 9066, which authorized and directed military commanders "to prescribe military areas … from which any or all persons may be excluded, and with respect to which, the right of any person to enter, remain in, or leave shall be subject to whatever restrictions the Secretary of War or the appropriate Military Commander may impose in his discretion." Under the authority of this executive order, roughly 112,000 men, women, and children of Japanese descent — nearly two-thirds of which were American citizens — were detained in concentration camps.

How did the camps get their start?

With the benefit of a nearly 80-year perspective, it's clear that the internment of Japanese Americans was racially motivated. In response to Japan's growing military power in the buildup to World War II, President Roosevelt commissioned two reports to determine whether it would be necessary to intern Japanese Americans should conflict break out between Japan and the U.S. Neither's conclusions supported the plan, with one even going so far as to "certify a remarkable, even extraordinary degree of loyalty among this generally suspect ethnic group." But of course, the Pearl Harbor attacks proved to be far more persuasive than these reports.

Pearl Harbor turned simmering resentment against the Japanese to a full boil, putting pressure on the Roosevelt administration to intern Japanese Americans. Lieutenant General John DeWitt, who would become the administrator of the internment program, testified to Congress

"I don't want any of them here. They are a dangerous element. There is no way to determine their loyalty... It makes no difference whether he is an American citizen, he is still a Japanese. American citizenship does not necessarily determine loyalty... But we must worry about the Japanese all the time until he is wiped off the map."

DeWitt's position was backed up by a number of pre-existing anti-immigrant groups based out of the West Coast, such as the Joint Immigration Committee and the Native Sons and Daughters of the Golden West. For many, the war simply served as an excuse to get rid of Japanese Americans. In an interview with the Saturday Evening Post, Austin Anson, the managing secretary of the Salinas Vegetable Grower-Shipper Administration, said:

"We're charged with wanting to get rid of the Japs for selfish reasons. We do. It's a question of whether the White man lives on the Pacific Coast or the brown men. ... If all the Japs were removed tomorrow, we'd never miss them in two weeks because the White farmers can take over and produce everything the Jap grows. And we do not want them back when the war ends, either."

Ironically for Anson, the mass deportation of Japanese Americans under Executive Order 9066 meant there was a significant shortage of agricultural labor. Many Caucasians left to fight the war, so the U.S. signed an agreement with Mexico to permit the immigration of several million Mexicans agricultural workers under the so-called bracero program.

Life in the camps

Japanese American concentration camp

Hulton Archive/Getty Images

Circa 1943: Aerial view of a Japanese American relocation center in Amache, Colorado, during World War II. Each family was provided with a space 20 by 25 ft. The barracks were set in blocks and each block was provided with a community bath house and mess hall.

For the most part, Japanese Americans remained stoic in the face of their incarceration. The phrase shikata ga nai was frequently invoked — the phrase roughly translates to "it cannot be helped," which, for many, represents the perceived attitude of the Japanese people to withstand suffering that's out of their control.

Initially, most Japanese Americans were sent to temporary assembly centers, typically located at fairgrounds or racetracks. These were hastily constructed barracks, where prisoners were often packed into tight quarters and made to use toilets that were little more than pits in the ground. From here, they were relocated to more permanent camps — replete with barbed wire and armed guards — in remote, isolated places across the seven states of California, Arizona, Colorado, Wyoming, Idaho, Utah, and Arkansas.

Many of these camps, also known as War Relocation Centers, were little better than the temporary assembly centers. One report described the buildings as "tar paper-covered barracks of simple frame construction without plumbing or cooking facilities of any kind." Again, overcrowding was common.

As a result, disease became a major concern, including dysentery, malaria, and tuberculosis. This was problematic due to the chronic shortage of medical professionals and supplies, an issue that was not helped by the War Relocation Authority's decision to cap Japanese American medical professional's pay at $20 a month (about $315 in 2019 dollars), while Caucasian workers had no such restriction. As a comparison, Caucasian nurses earned $150 ($2,361) a month in one camp.

The U.S. government also administered loyalty questionnaires to incarcerated Japanese Americans with the ultimate goal of seeing whether they could be used as soldiers and to segregate "loyal" citizens from "disloyal" ones. The questionnaires often asked whether they would be willing to join the military and if they would completely renounce their loyalty to Japan. Due to fears of being drafted, general confusion, and justified anger at the U.S. government, thousands of Japanese Americans "failed" the loyalty questionnaire and were sent to the concentration camp at Tule Lake. When Roosevelt later signed a bill that would permit Japanese Americans to renounce their citizenship, 98 percent of the 5,589 who did were located at Tule Lake. Some apologists cite this an example of genuine disloyalty towards the U.S., but this argument clearly ignores the gross violation of Japanese Americans' rights. Later, it became clear that many of these renunciations had been made under duress, and nearly all of those who had renounced their citizenship sought to gain it back.

Since many children lived in the camps, they came equipped with schools. Of course, these schools weren't ideal — student-teacher ratios reached as high as 48:1, and supplies were limited. The irony of learning about American history and ideals was not lost on the students, one of whom wrote in an essay --

"They, the first generation [of Japanese immigrants], without the least knowledge of the English language nor the new surroundings, came to this land with the American pioneering spirit of resettling. ...Though undergoing many hardships, they did reach their goal only to be resettled by the order of evacuation under the emergency for our protection and public security."

Potentially the best part of life in the camps — and the best way for determined prisoners to demonstrate their fundamental American-ness — was playing baseball. One camp even featured nearly 100 baseball teams. Former prisoner Herb Kurima recalled the importance of baseball in their lives in an interview with Christian Science Monitor. "I wanted our fathers, who worked so hard, to have a chance to see a ball game," he said. "Over half the camp used to come out to watch. It was the only enjoyment in the camps."

The aftermath

When the camps finally closed in 1945, the lives of the incarcerated Japanese Americans had been totally upended. Some were repatriated to Japan, while others settled in whichever part of the country they had been arbitrarily placed in. Those who wished to return to the West Coast were given $25 and a train ticket, but few had anything to return to. Many had sold their property to predatory buyers prior to being incarcerated, while theft had wiped out whatever else they had left behind. Many, many years later, the 1988 Civil Liberties Act mandated that each surviving victim be paid $20,000, though that seems like a small fine to pay for irrevocably changing the courses of more than 100,000 lives.