Why is 18 the age of adulthood if the brain can take 30 years to mature?

Neuroscience research suggests it might be time to rethink our ideas about when exactly a child becomes an adult.

Why is 18 the age of adulthood if the brain can take 30 years to mature?
  • Research suggests that most human brains take about 25 years to develop, though these rates can vary among men and women, and among individuals.
  • Although the human brain matures in size during adolescence, important developments within the prefrontal cortex and other regions still take place well into one's 20s.
  • The findings raise complex ethical questions about the way our criminal justice systems punishes criminals in their late teens and early 20s.

At what age does someone become an adult? Many might say that the 18th birthday marks the transition from childhood to adulthood. After all, that's the age at which people can typically join the military and become fully independent in the eyes of the law.

But in light of research showing our brains develop gradually over the course of several decades, and at different paces among individuals, should we start rethinking how we categorize children and adults?

"There isn't a childhood and then an adulthood," Peter Jones, who works as part of the epiCentre group at Cambridge University, told the BBC. "People are on a pathway, they're on a trajectory."

The prefrontal cortex, cerebellum and reward systems

One key part of that trajectory is the development of the prefrontal cortex, a significant part of the brain, in terms of social interactions, that affects how we regulate emotions, control impulsive behavior, assess risk and make long-term plans. Also important are the brain's reward systems, which are especially excitable during adolescence. But these parts of the brain don't stop growing at age 18. In fact, research shows that it can take more than 25 years for them to reach maturity.

The cerebellum also affects our cognitive maturity. But unlike the prefrontal cortex, the development of the cerebellum appears to depend largely on environment, as Dr. Jay Giedd, chair of child psychiatry at Rady Children's Hospital-San Diego, told PBS:

"Identical twins' cerebellum are no more alike than non-identical twins. So we think this part of the brain is very susceptible to the environment. And interestingly, it's a part of the brain that changes most during the teen years. This part of the brain has not finished growing well into the early 20s, even. The cerebellum used to be thought to be involved in the coordination of our muscles. So if your cerebellum is working well, you were graceful, a good dancer, a good athlete.

But we now know it's also involved in coordination of our cognitive processes, our thinking processes. Just like one can be physically clumsy, one can be kind of mentally clumsy. And this ability to smooth out all the different intellectual processes to navigate the complicated social life of the teen and to get through these things smoothly and gracefully instead of lurching. . . seems to be a function of the cerebellum."

The effects environment can bring upon the cerebellum even further complicate the question when does a child become an adult, considering the answer might depend on the kind of childhood an individual experienced.

Adulthood and the criminal justice system

These factors of cognitive develop raise many philosophical questions, but perhaps none are as important as those related to how we punish criminal, especially among young men, whose brains develop an average of two years later than women.

"The preponderance of young men engaging in these deadly, evil, and stupid acts of violence may be a result of brains that have yet to fully developed," Howard Forman, an assistant professor of psychiatry at Albert Einstein College of Medicine, told Business Insider.

So, does that mean young criminals — say, 19- to 25-year-olds — should be receive the same punishment as a 35-year-old who commits the same crime? Both criminals would still be guilty, but each might not necessarily deserve the same punishment, as Laurence Steinberg, a professor of psychology at Temple University, told Newsweek.

"It's not about guilt or innocence... The question is, 'How culpable are they, and how do we punish them?'"

After all, most countries have separate juvenile justice systems to deal with children who commit crimes. These separate systems are predicated on the idea that there ought to be a spectrum of culpability that accounts for a criminal's age. So, if we assume that the importance of age in the eyes of the justice system is based largely on cognitive differences between children and adults, then why shouldn't that culpability spectrum be modified to better match the science, which clearly shows that 18 is not the age at which the brain is fully matured?

Whatever the answer, society clearly needs some definition of adulthood in order to be able to differentiate between children and adults in order to function smoothly, as Jones suggested to the BBC.

"I guess systems like the education system, the health system and the legal system make it convenient for themselves by having definitions."

But that doesn't mean these definitions make sense outside of a legal context.

"What we're really saying is that to have a definition of when you move from childhood to adulthood looks increasingly absurd," he said. "It's a much more nuanced transition that takes place over three decades."

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COVID and "gain of function" research: should we create monsters to prevent them?

Gain-of-function mutation research may help predict the next pandemic — or, critics argue, cause one.

Credit: Guillermo Legaria via Getty Images
Coronavirus

This article was originally published on our sister site, Freethink.

"I was intrigued," says Ron Fouchier, in his rich, Dutch-accented English, "in how little things could kill large animals and humans."

It's late evening in Rotterdam as darkness slowly drapes our Skype conversation.

This fascination led the silver-haired virologist to venture into controversial gain-of-function mutation research — work by scientists that adds abilities to pathogens, including experiments that focus on SARS and MERS, the coronavirus cousins of the COVID-19 agent.

If we are to avoid another influenza pandemic, we will need to understand the kinds of flu viruses that could cause it. Gain-of-function mutation research can help us with that, says Fouchier, by telling us what kind of mutations might allow a virus to jump across species or evolve into more virulent strains. It could help us prepare and, in doing so, save lives.

Many of his scientific peers, however, disagree; they say his experiments are not worth the risks they pose to society.

A virus and a firestorm

The Dutch virologist, based at Erasmus Medical Center in Rotterdam, caused a firestorm of controversy about a decade ago, when he and Yoshihiro Kawaoka at the University of Wisconsin-Madison announced that they had successfully mutated H5N1, a strain of bird flu, to pass through the air between ferrets, in two separate experiments. Ferrets are considered the best flu models because their respiratory systems react to the flu much like humans.

The mutations that gave the virus its ability to be airborne transmissible are gain-of-function (GOF) mutations. GOF research is when scientists purposefully cause mutations that give viruses new abilities in an attempt to better understand the pathogen. In Fouchier's experiments, they wanted to see if it could be made airborne transmissible so that they could catch potentially dangerous strains early and develop new treatments and vaccines ahead of time.

The problem is: their mutated H5N1 could also cause a pandemic if it ever left the lab. In Science magazine, Fouchier himself called it "probably one of the most dangerous viruses you can make."

Just three special traits

Recreated 1918 influenza virionsCredit: Cynthia Goldsmith / CDC / Dr. Terrence Tumpey / Public domain via Wikipedia

For H5N1, Fouchier identified five mutations that could cause three special traits needed to trigger an avian flu to become airborne in mammals. Those traits are (1) the ability to attach to cells of the throat and nose, (2) the ability to survive the colder temperatures found in those places, and (3) the ability to survive in adverse environments.

A minimum of three mutations may be all that's needed for a virus in the wild to make the leap through the air in mammals. If it does, it could spread. Fast.

Fouchier calculates the odds of this happening to be fairly low, for any given virus. Each mutation has the potential to cripple the virus on its own. They need to be perfectly aligned for the flu to jump. But these mutations can — and do — happen.

"In 2013, a new virus popped up in China," says Fouchier. "H7N9."

H7N9 is another kind of avian flu, like H5N1. The CDC considers it the most likely flu strain to cause a pandemic. In the human outbreaks that occurred between 2013 and 2015, it killed a staggering 39% of known cases; if H7N9 were to have all five of the gain-of-function mutations Fouchier had identified in his work with H5N1, it could make COVID-19 look like a kitten in comparison.

H7N9 had three of those mutations in 2013.

Gain-of-function mutation: creating our fears to (possibly) prevent them

Flu viruses are basically eight pieces of RNA wrapped up in a ball. To create the gain-of-function mutations, the research used a DNA template for each piece, called a plasmid. Making a single mutation in the plasmid is easy, Fouchier says, and it's commonly done in genetics labs.

If you insert all eight plasmids into a mammalian cell, they hijack the cell's machinery to create flu virus RNA.

"Now you can start to assemble a new virus particle in that cell," Fouchier says.

One infected cell is enough to grow many new virus particles — from one to a thousand to a million; viruses are replication machines. And because they mutate so readily during their replication, the new viruses have to be checked to make sure it only has the mutations the lab caused.

The virus then goes into the ferrets, passing through them to generate new viruses until, on the 10th generation, it infected ferrets through the air. By analyzing the virus's genes in each generation, they can figure out what exact five mutations lead to H5N1 bird flu being airborne between ferrets.

And, potentially, people.

"This work should never have been done"

The potential for the modified H5N1 strain to cause a human pandemic if it ever slipped out of containment has sparked sharp criticism and no shortage of controversy. Rutgers molecular biologist Richard Ebright summed up the far end of the opposition when he told Science that the research "should never have been done."

"When I first heard about the experiments that make highly pathogenic avian influenza transmissible," says Philip Dormitzer, vice president and chief scientific officer of viral vaccines at Pfizer, "I was interested in the science but concerned about the risks of both the viruses themselves and of the consequences of the reaction to the experiments."

In 2014, in response to researchers' fears and some lab incidents, the federal government imposed a moratorium on all GOF research, freezing the work.

Some scientists believe gain-of-function mutation experiments could be extremely valuable in understanding the potential risks we face from wild influenza strains, but only if they are done right. Dormitzer says that a careful and thoughtful examination of the issue could lead to processes that make gain-of-function mutation research with viruses safer.

But in the meantime, the moratorium stifled some research into influenzas — and coronaviruses.

The National Academy of Science whipped up some new guidelines, and in December of 2017, the call went out: GOF studies could apply to be funded again. A panel formed by Health and Human Services (HHS) would review applications and make the decision of which studies to fund.

As of right now, only Kawaoka and Fouchier's studies have been approved, getting the green light last winter. They are resuming where they left off.

Pandora's locks: how to contain gain-of-function flu

Here's the thing: the work is indeed potentially dangerous. But there are layers upon layers of safety measures at both Fouchier's and Kawaoka's labs.

"You really need to think about it like an onion," says Rebecca Moritz of the University of Wisconsin-Madison. Moritz is the select agent responsible for Kawaoka's lab. Her job is to ensure that all safety standards are met and that protocols are created and drilled; basically, she's there to prevent viruses from escaping. And this virus has some extra-special considerations.

The specific H5N1 strain Kawaoka's lab uses is on a list called the Federal Select Agent Program. Pathogens on this list need to meet special safety considerations. The GOF experiments have even more stringent guidelines because the research is deemed "dual-use research of concern."

There was debate over whether Fouchier and Kawaoka's work should even be published.

"Dual-use research of concern is legitimate research that could potentially be used for nefarious purposes," Moritz says. At one time, there was debate over whether Fouchier and Kawaoka's work should even be published.

While the insights they found would help scientists, they could also be used to create bioweapons. The papers had to pass through a review by the U.S. National Science Board for Biosecurity, but they were eventually published.

Intentional biowarfare and terrorism aside, the gain-of-function mutation flu must be contained even from accidents. At Wisconsin, that begins with the building itself. The labs are specially designed to be able to contain pathogens (BSL-3 agricultural, for you Inside Baseball types).

They are essentially an airtight cement bunker, negatively pressurized so that air will only flow into the lab in case of any breach — keeping the viruses pushed in. And all air in and out of the lap passes through multiple HEPA filters.

Inside the lab, researchers wear special protective equipment, including respirators. Anyone coming or going into the lab must go through an intricate dance involving stripping and putting on various articles of clothing and passing through showers and decontamination.

And the most dangerous parts of the experiment are performed inside primary containment. For example, a biocontainment cabinet, which acts like an extra high-security box, inside the already highly-secure lab (kind of like the radiation glove box Homer Simpson is working in during the opening credits).

"Many people behind the institution are working to make sure this research can be done safely and securely." — REBECCA MORITZ

The Federal Select Agent program can come and inspect you at any time with no warning, Moritz says. At the bare minimum, the whole thing gets shaken down every three years.

There are numerous potential dangers — a vial of virus gets dropped; a needle prick; a ferret bite — but Moritz is confident that the safety measures and guidelines will prevent any catastrophe.

"The institution and many people behind the institution are working to make sure this research can be done safely and securely," Moritz says.

No human harm has come of the work yet, but the potential for it is real.

"Nature will continue to do this"

They were dead on the beaches.

In the spring of 2014, another type of bird flu, H10N7, swept through the harbor seal population of northern Europe. Starting in Sweden, the virus moved south and west, across Denmark, Germany, and the Netherlands. It is estimated that 10% of the entire seal population was killed.

The virus's evolution could be tracked through time and space, Fouchier says, as it progressed down the coast. Natural selection pushed through gain-of-function mutations in the seals, similarly to how H5N1 evolved to better jump between ferrets in his lab — his lab which, at the time, was shuttered.

"We did our work in the lab," Fouchier says, with a high level of safety and security. "But the same thing was happening on the beach here in the Netherlands. And so you can tell me to stop doing this research, but nature will continue to do this day in, day out."

Critics argue that the knowledge gained from the experiments is either non-existent or not worth the risk; Fouchier argues that GOF experiments are the only way to learn crucial information on what makes a flu virus a pandemic candidate.

"If these three traits could be caused by hundreds of combinations of five mutations, then that increases the risk of these things happening in nature immensely," Fouchier says.

"With something as crucial as flu, we need to investigate everything that we can," Fouchier says, hoping to find "a new Achilles' heel of the flu that we can use to stop the impact of it."

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Credit: Hà Nguyễn via Unsplash
Sex & Relationships
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