Pruning of neurons: how forgetting keeps your brain efficient

Humans are a forgetful species.

While we have an amazing ability to remember complex information and patterns, our brains can be given so much information that if we remembered everything, it would be a jumbled mess and impossible to remember any specific fact.

Imagine that remembering something is like finding a pair of socks to wear. For most of us, that should be easy enough as we have a few pairs to choose from, already paired together in the drawer. Not much effort involved since they are relatively organised. Now imagine if instead, you had to find a pair by pulling random socks out of a dark bag you could not see into, and this bag contained not only all of the socks you now own, but all of the socks you have ever worn (including your baby socks), as well as every sock you ever saw someone on the street or your TV wearing, read about or could even imagine.

That chaos is what trying to remember would be like if every piece of information you ever came across were randomly stored to your memories. It would quickly become not just inefficient and cluttered, but unmanageable.

And our brains hate inefficiency. They always prefer to use the least amount of energy possible, and this including using memories instead of processing new information.

Our brain’s roughly 86 billion neurons, each having the possibility to connect with ten thousand other neurons, means there are hundreds of trillions of synapses in your brain. Amazingly, it is estimated that a 3 year old child might have up to a quadrillion synapses between neurons, but this then is reduced by several hundred trillion to end up at our adult total number.

What is happening over this time period in our brain is fascinating. The brain is noticing which neuronal networks appear to fire together repeatedly or powerfully, and equates that as these being useful, important and worth keeping. So it wires these networks together through increasing the myelination of these cells, and the strength of the synapses between them. This makes those networks stronger, and forms memories and automatic behaviours.

But what happens to those synapses on neural networks which are not used often, or at all?

Well, those are the ones which are removed to allow the others to become stronger. They are “forgotten”, and this happens through a process called synaptic pruning.

During pruning, the synapse between two neurons is destroyed, either by the axon reaching between two neurons retracting (which increases the distance so the synapse can no longer function), or through special immune cells in the brain called microglia destroying the connection. The exact nature of how these cells identify which synapses to destroy or protect is not well understood, but it is likely related to the existence of certain proteins around the synapse.

What is especially interesting is how this process is especially active while we sleep. Sleep was long known to be important in the development of memories, but now we also understand that sleep is important for pruning unnecessary synapses, thereby keeping our brains working effectively.

There is a danger that as we get older, the networks which are used more are continually strengthened while those which are exercised less are weakened and pruned. If we continue doing the same thing day in and day out, this may result in us becoming cognitively fixed, and being less able to ignore the knowledge we have previously learned even when we need to be more creative.

So while creativity relies on new associations between existing knowledge, pruning is not necessarily bad for creativity even though it results in fewer weak connections in the brain.

Pruning helps us practice and develop our skills, as well as build up expertise in a specific domain. This in turn can help us understand the challenges in a domain, and iterate to find stronger ideas rather than just any idea.

Plus, pruning is a natural process which keeps our brains working at peak efficiency, which means that when we do need to develop new ideas, there is enough excess energy available for us to come up with truly original ideas.

So if you can’t remember all of your high-school spanish homework, don’t worry. You pruned it for a reason.

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Nick Skillicorn

Chief Editor, Founder & CEO at Improvides Innovation Consulting

Creativity & Innovation expert: I help individuals and companies build their creativity and innovation capabilities, so you can develop the next breakthrough idea which customers love. Chief Editor of Ideatovalue.com and Founder / CEO of Improvides Innovation Consulting. Coach / Speaker / Author / TEDx Speaker / Voted as one of the most influential innovation bloggers.