Does the Brain Really Stop Developing by Age 25?

I almost didn’t pass all the skills taught in kindergarten.

I had mastered everything from cutting paper with scissors to drawing with crayons – everything except for tying my shoes.

I practiced every day: go under the bridge, make a loop, keep a long tail, wrap it around, and pull… darn it! Every time I got to the final step, all my hard work disappeared before my eyes as I watched the strings come out straight. I couldn’t figure out for the life of me how to do it, and I almost gave up altogether out of frustration. That is, until my next-door neighbor and best friend at the time taught me the Bunny Ears method.

“It’s easy,” she smiled as she made two loops and knotted them together with ease. After several attempts, I was able to tie my aqua blue tennis shoes to perfection. By the time summer rolled around, there was a green check in every box on my skills checklist. (I suppose I would’ve figured out the first shoe-tying technique eventually, but there was a strict time limit on this task. And a loophole – or two – wasn’t going to hurt).

Many people suffering from brain and spinal injuries face a similar issue: they have to re-learn how to tie their shoes, how to walk, and how to do everything else us able-bodied people take for granted every day of our lives. But how is it possible for an adult to learn something new late in life, especially after extensive damage? I thought our brains stopped changing at some point?

That’s what I thought, too. In fact, that’s what doctors and scientists around the globe believed for decades. Once you reach a certain age, your brain stops changing. It’s more or less set in stone. This was dogma. Scientists who suggested otherwise were mocked, even if they had proof. Their research was discredited, their methods invalidated.

This principle was drilled into the brains of medical students and young scientists everywhere: “Once the development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably. In the adult centers, the nerve paths are something fixed, ended, and immutable.” Eventual “solidification” of the brain was the leading ideology advanced by Ramon y Cajal, the father of modern neuroscience, among other prominent figures in the field. End of discussion.

Today, we know that this is far from the truth.

There’s an overwhelming amount of evidence showing that the brain continues to grow new neurons (or brain cells) throughout adulthood, which is a process known as neurogenesis. However, that’s an entirely different conversation, one that’s a bit more disputed and requires its own article – and its own semester-long class, book, and PhD. 

For now, we’ll just stick to one thing that we know for sure: that our brains continue to change throughout the entirety of our lives. We say that the brain is “plastic” for this reason, or that it’s like a muscle. But not in the physical sense; the living brain looks more like a pudding of tissue and blood unlike the typical, hardened version you might see in an anatomy lab. (Perhaps imagine clay, instead; the pudding image isn’t too easy on the eyes). And most of the time, your brain is changing without any conscious effort. 

This is thanks to one of the most fascinating properties of the marvelous brain: neuroplasticity. Neuroplasticity refers to your brain’s ability to rewire, or change. Rewiring entails physical alterations in the brain’s circuitry, and it’s happening every minute of every day. Your brain is constantly adapting to the world around you. Hebbian Theory, a founding principle in the field of neuroscience, explains this phenomenon. 

What is Neuroplasticity?

In 1949, Canadian psychologist Dr. Donald O. Hebb shared with the world a truly remarkable discovery: neurons that fire together, wire together. Neurons are the basic building blocks of the brain that create networks and give rise to all thoughts, emotions, and behaviors. When a neuron repeatedly communicates with another neuron via electrical and chemical signals, their connection strengthens, and the first neuron becomes increasingly better at activating the second neuron. Think of it like speed dial: instead of typing out your mom’s entire phone number, you might just hit “1.” It’s faster and takes less effort. You don’t have to put much thought into it. Several neurons then come together to form circuits, and circuits become more efficient with repetition. 

Neuroplasticity provides the basis for all learning and habit-forming. This is what allows you to learn algebra or how to play tennis. Another famous phrase coined to describe this process is “use it or lose it.” When a task is performed enough times (say, parallel parking), your brain reinforces the activity of the neurons involved in the planning and execution of the movement. Eventually, after “using” these neural pathways enough, the motion becomes somewhat automatic. Something like parallel parking, that once seemed impossible (for me, at least), becomes routine. What about the “lose it” part?

If you do not persistently use these circuits, though (for instance, you move out of the city and no longer need to parallel park every day), the circuits lose their strength, and some links in the chain may disconnect altogether. In this case, it requires much more effort to re-establish the connections back to the point where the networks were nearly running on autopilot. You may just have to learn how to parallel park all over again.

If that’s still not making total sense, you’re not alone. Let’s look at an analogy.

Visualizing the Plastic Brain

Imagine that you’re walking through a jungle. Maybe you’re stuck in Jumanji, or maybe you’re Indiana Jones. You use a machete to hack down any overgrown plants and branches in the way. After covering some distance, a somewhat distinguished pathway emerges behind you. The clearing here is representative of a neural connection forming in your brain, which is just one neuron signaling another. You, the traveler, might represent an electrical impulse or neurotransmitter, which is how brain cells talk to each other.

After several days, the path is well traveled, it’s easy to see, tall grass has been stomped down, branches have been cleared out of the way, and the ground has been imprinted to the point where you can see dirt. The next time you enter that jungle, instead of creating a new trail, you will automatically take the forged one. Since you no longer have to go through the hassle of clearing things out of the way, you walk through it much more quickly this time. Why would you waste time by traveling along an undeveloped path when there is an established one available?

This whole process takes time, energy, and repetition. Repetition is key. Even though typing on a computer is a breeze for most of us, it once took several seconds just to type a few words. Today, you probably don’t even have to look at the keyboard while typing. Learning new skills doesn’t happen overnight because your neurons need tons of repetition in order to activate more quickly and with more ease. Adequate sleep is also required to consolidate these networks, but, like neurogenesis, that warrants its own conversation.