The Brain, Neurons, and human development
Throughout our early years our brain undergoes two periods of significant change. Most of us are familiar with the rapid development of movement and speech that infants experience within their first year. The second, and less understood, major change that occurs in our brain is during adolescence. This seismic shift takes place in our frontal cortex, which is the master control for the rest of our brain, and is critical to our development into healthy adults.
In order to better understand the importance of what happens to our brain during adolescents, it is best if we first begin with the infants brain.
When we are born we have roughly the same number of neurons that we will have when we are an adult. However, we have many more neural connections than we will ever have again. This large number of neural connections is one of the reasons that we can’t control our body very well. There are too many signals being sent when we try to do a specific task. This is why a baby’s movements are so uncoordinated. They have too many neurons firing and the signals are getting crossed.
As we develop we begin to strengthen the connections that are working for us, and prune the neural connections that are not being used.
As we progress through childhood our brain looses neural density and gains neural specificity . We start life with more neural connections than we need, and through using some and not using others our brain strengthens the connections that are working and discards the connections that are not. This process leads to our brain being less dense, so when you call someone “dense”, maybe they just have too many neural connections…
If you watch a baby try to eat with a spoon for the first time you will see this process in actions. They try their hardest to get that spoon to their mouth but end up with it hitting their forehead. If we could see inside of their brain at this moment we would see the neural pathways for Arm Movement lighting up, but the signals for “move to mouth” are also connected to the signals for “touch head” and “smear on face”.
As the baby practices, the connections for “move to mouth” become clearer as they discard any unwanted cross connections with the “touch head” and “smear on face” neural pathways.
When we practice a skill, our brain is literally getting less dense.
The unfortunate part about this process is that our brain has a “use it or lose it” function. A common example of this is language acquisition. If a child is regularly exposed to a language within the first 6 months they will retain the ability to recognize the subtle sounds the are unique to that language. However, if we try to learn a new language, say in middle and high school, then we will struggle with the subtle vocal differences that are alien to our native tongue. This is because the connections in our brain that would have been associated with those specific sounds have already been pruned away because they were not being used during this critical part of our brain development.
I would like to mention here, and I will mention it again throughout this article, that the human brain is amazing in its ability to learn and adapt. It is never too late to acquire a skill, it is merely easier to do so at specific stages in our life.
The adolescent brain
It is during the early years of adolescence that we have another veritable explosion of neuronal growth. While the infants growth focused primarily on the language and motor control areas of the brain, the adolescent has a significant increase in neural density within their frontal cortex.
This area of the brain is significant because of its role in short-term planning, executive functioning, cognitive reasoning, attention, and focus. All of which we can see adolescents struggling with as they develop.
Just as a baby struggles to pickup a spoon because it has too many neurons firing, an adolescent can struggle to focus on their homework because they have too many neurons firing when they try to complete the task. This is different from lacking the ability to do so, as can be the case with younger children. Rather, the adolescent can sense that they can do it (they have the neural pathways), but they struggle when they actually try (the “sit down and focus” signals are getting lost amongst the tangle of new neuronal connections). This can add to the frustration that is already felt when doing a difficult task.
However, just as a baby prunes and strengthens specific neural connections through use, the adolescent’s frontal cortex undergoes the same process. As the adolescent practices critical thinking, planning and focusing, they are strengthening the neural pathways that are associated with those tasks.
One again we find ourselves in a critical developmental period, where new neural connections are being formed at a rapid pace. Most of the neural pathways that we will use as an adult are formed within the first few years of this process, and we spend the rest of our adolescence trying to filter the signal from the noise.
It is generally understood that our frontal cortex continues to develop until our early to mid 20’s. We are just now beginning to understand what is going on in the brain during this period of development. We now understand that the neural pathways that we develop during adolescence will be with use through the rest of our adult life. The skills and habits that we form at this time will dramatically shape who we will become in our future.
Opening up the brain
Up to this point I have been using general terminology to describe a process that effects us all, in the hopes of providing some context for the struggles that the adolescents in our life are going through. The rest of this article will dive a bit deeper into the science and anatomy of the processes described above for those that are curious.
To begin, we must first understand the anatomy of a neuron.
There are many parts to a neuron, but for our purposes we are going to focus on the three primary aspects that are involved in passing information: The Dendrites, Axon, and the Axon Terminals.
Simply put, the Dendrites take in signals. Once the signals they are receiving reach a critical point the neuron fires its own electrical signal down the Axon to the Axon Terminals, which in turn are connected to other neuron’s Dendrites.
Naturally this process is much more complex and interesting than we will be going over here. But for our purposes we just need to understand two main points: The more dendrites there are the more neural connections there are, and signals are passed down through the Axon.
It is the dendrites that get pruned through disuse and it is the Axons that get strengthened through regular use. The process of strengthening the Axon is called Myelination.
Through use, the neuron begins to develop what is called a Myelin Sheath over its Axon. This sheath provides insulation to the Axon, increasing its signal transmission speed up to 100 fold. These Myelin Sheaths lend a permanence to the neuron and increases its efficiency.
A classic example of a particular pathway being myelinated can be found in learning to drive. In the beginning you are needing to think about all the different steps involved in driving: Break, gas, steering, other cars. But eventually driving becomes natural and we do not need to think about it. If we could zoom into the neural pathways that are involved in driving we would be able to see these neurons forming more myelination on their axons, along with a pruning of dendrites and neural connections that are not being used. After years of practice, a particular neural pathway becomes a lean, mean, myelinated machine. When this happens the signals down that pathway are fast due to myelination and there are few “wrong turns” for the signals to make. This is in part why it can be so difficult to change an old habit. Those neural pathways are well myelinated and other possible pathways have died off.
While we still can’t zoom into specific neural pathways, we can measure the general amount of myelination and dendrite density in any particular area of the brain through MRI studies. Many people have heard about white and grey matter in the brain. Turns out that white matter is myelination and density of the brain equates to number of dendrites. With these two pieces of information, we can effectively measure the development of any particular region of the brain.
What the studies have shown us is that, beginning in the early stages of adolescence, our prefrontal cortex undergoes significant levels of synaptogenesis, which is followed by a steady increase in the amount of white matter as we continue to develop.
In short, the primary control center for our brain goes through a rapid, tangled, messy growth in the beginning of our adolescence, and we spend the rest of our teenage years trying to untangle it and strengthen the connections that are useful to us.
The take away from all of this information, at least for myself, is as follows: It is important to practice the cognitive skills that are associated with our frontal cortex when we are in our adolescence. This is a period of “use it or lose it” when it comes to essential cognitive skills such as focus, planning, risk assessment and executive functioning. While at the same time, we must give adolescents all the understanding in the world when they struggle with these skills. They are but a tot who is trying their hardest to fire the correct neural pathway to get that spoon to their mouth.