When Do Our Brains Really Grow Up? New Research Challenges Old Assumptions

We’ve all heard the phrase “young and dumb” to describe the sometimes questionable choices of youth. But what if our brains aren’t really that different as kids versus adults?

A new study from neuroscientist Bobby Kasthuri and his team at Argonne National Laboratory is forcing us to rethink everything we thought we knew about brain development.

Mice & Monkeys More Similar Than We Realized

The study looked at the brains of mice, which typically live just two years, and monkeys, which can live up to 25 years. Shockingly, they found that the synapses in the brains of both species develop on the exact same timeline. This flies in the face of the long-held assumption that brain development happens much faster in short-lived species like mice compared to primates.^(ref)

So a two-month-old mouse brain and a two-month-old monkey brain are actually at very similar developmental stages, despite their vastly different lifespans. Mind blown! This means a lot of past research comparing young mouse brains to older primate brains to study things like autism and other disorders wasn’t really comparing apples to apples.

In fact, when Kasthuri’s team previously compared adult mouse and primate brains, they found primate neurons have way fewer connections than mouse neurons. At the time, they chalked it up to primates being “smarter.” Now, they realize they were actually comparing a young adult mouse to a much older primate. Oops!

The Fascinating Timeline of Brain Development

So, what does normal brain development look like? It’s a complex process that starts before we’re even born:

• By 35 days after conception, the early structures of the brain and spinal cord are forming, and the first neurons are produced.
• Around 100 days after conception, neurons are born deep in the brain at an astonishing rate of about 15 million per hour. They then migrate to their final positions, guided by molecular signals.
• At birth, the brain is only about 25% the size of an adult brain. Then a period of rapid growth begins – by age 2, the brain reaches 80% of its adult size as neuron circuitry matures and protective glial cells are born.
• The brain reaches its full size around age 14, but the circuitry continues to rewire until early adulthood, around age 25.

Experience plays a key role in shaping the brain’s development throughout this process. The connections between neurons are strengthened or pruned based on the input they receive. This neuroplasticity allows the brain to adapt and learn from its environment.^(ref)

Rethinking Brain Aging & Disorders

These new insights into brain development have major implications for how we understand brain aging and disorders. Functional brain connectivity, the way different regions of the brain interact, undergoes complex changes across the lifespan:

• In early childhood, brain networks start to segregate and become more specialized.
• From adolescence to early adulthood, brain networks become more integrated.
• In middle age, this shifts and brain networks start to become less segregated and reorganize on a large scale.
• In older age, brain regions become less functionally specialized, which is associated with cognitive decline.

Understanding these changes could help develop better-targeted treatments for brain disorders at different ages. For example, many psychoactive medications given to pregnant women and children have not been thoroughly tested for safety and long-term effects on the developing brain. More research in this area is critical.

There is also hope that interventions could slow or even reverse certain aspects of brain aging. Animal studies suggest that stem cells could potentially replenish declining neural stem cells. 

Rare individuals over 80, known as “SuperAgers,” who have remarkable memory abilities, may hold clues to resisting age-related cognitive decline.

The Secrets of the Human Brain

While the new findings on mice and monkeys are groundbreaking, the implications for humans are still a bit of a mystery. Humans develop complex skills like walking and talking much later than other mammals, so our brains may be on a totally different schedule.

Kasthuri suspects “something remarkable, something magical” is happening in human brain development compared to other species. Collaboration between neuroscientists and other experts will be key to unraveling these secrets and translating the findings into real-world applications.

What is clear is that the brain is an incredibly complex and ever-changing organ. From the womb to old age, our brains constantly develop, adapt, and transform in ways we are only beginning to understand.

As research continues to evolve, it will open up exciting new possibilities for optimizing brain health and treating neurological disorders across the lifespan. The more we learn about the intricacies of the brain, the better equipped we’ll be to unlock its full potential.