Friday, 3 August 2012

Neural Pruning, or: "Why is my teen so impulsive?"

Almost every parent sports a few new grey hairs as their children navigate through their teen years, and many wonder why the teenage phase of development is often fraught with impulsive, reckless behaviour and raging emotional outbursts.  Rising hormone levels play their part to be sure, but a great deal of the impulsiveness we see in teens and young adults lies within how the human brain develops and organizes.  It’s all about the neurons.

Neurons are the little nerve cells in our brains that connect to each other through electrical and chemical signaling.  They comprise the circuitry of our brains and keep our heart beating, our lungs breathing, our temperature regulated and a millions other complex tasks that happen automatically to keep us alive, aware, and safe.  They are also the circuitry in our cortex that allow us to feel, learn, reason, plan, imagine, and act.

Each neuron has about 10,000 connections to other neurons.  At the time of our birth we have about 10 billion neurons, but our brains continue to grow into our teen years and will reach 80 billion to 120 billion in number.  So taking an average of 100 billion neurons, each with 10,000 connections gives us 1,000,000,000,000,000 circuits inside the confines of our brains – each capable of activating as we encounter a new stimulus or choice.  And with that many active connections, a teen’s brain is a pretty busy place.  And sometimes it’s a confusing place as the neural connections compete with each other – and this is why we often see the poor judgment, impulsiveness, and at-risk behaviour in our teens.  This is also why we see the rapidly cycling highs and lows of emotion and why some teens resort to drugs or alcohol or self-injury as a means dial back the sometimes overwhelming activity inside their head.

So why do we have so many connections that they actually seem to cause us problems?  It’s because the brain is designed around redundancy – we have two of almost everything we need and – as noted above - way more connections than we require.

Now here’s the good news; Because nature intended us to have more neural connections than we need, it also provided our brain with a means to organize those connections.  As we mature, our brain prunes excess connections.  First, little-used connections are pruned as part of a “use it or lose it” strategy.  Second, troublesome connections are pruned – connections that duplicate messages that create that impulsive behaviour or raging emotions are cut out.  Outwardly, we see this as “learning” and “maturing”.

This pruning process starts in infancy and is completed in early adulthood, which is why we see our wild teenagers gradually calm down as they approach their mid 20s.

So, knowing why our teens seem to be out of control at times won’t slow the greying of our hair, but it will hopefully help us to understand that these behaviours are a normal stage of development and will one day pass.

Aaron D. McClelland, RPCc

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