Synaptic pruning is a process whereby neurons are eliminated from the brain. It occurs when there is too much activity within the brain and not enough energy left over to support it. A neuron’s job is to fire off electrical impulses which travel along nerve fibers until they reach their destination (synapses). At these junctions, the signals cross into one another’s bodies and form new connections between them. These connections are called synapses.
When a neuron fires, its signal travels through the synapse and then out of the body of the neuron. If there is no other cells or molecules nearby to receive this signal, it will continue on to its destination.
But if there are many other cells or molecules near the neuron, some of those cells may pick up on this noise and send their own messages back to the cell that fired off your message. You might get a response back saying “Hey! I heard you!” or maybe nothing at all. Either way, the neuron still sent its message to the rest of your brain.
The problem arises when too many neurons are firing off at once, because now there isn’t enough energy left over to support them all. They start dying down and eventually they cease altogether.
This is when “neural pruning” occurs. If you’re lucky, the important ones made enough connections and survived. If not, then sorry, but those connections just aren’t there anymore.
While this may seem counter-productive to our survival as a species, it can be helpful in some ways. For instance, if you have too much information coming into your brain, it can lead to anxiety and panic attacks (which are caused by your brain overloading on incoming signals).
Neural pruning can act as a preventative measure against this. It also allows us to focus on the most important things because if all of our senses were running at full-capacity at all times, we wouldn’t be able to pay attention and retain information effectively.
The average human will experience over 100,000,000 miles of neural pathways throughout their life time. It is essential that some of these don’t get used in order for the rest to stay intact.
This medical procedure has recently been popularized in the science fiction novel “Ready Player One” by Ernest Cline and later in the movie of the same name.
Sources & references used in this article:
Synaptic pruning by microglia is necessary for normal brain development by RC Paolicelli, G Bolasco, F Pagani, L Maggi… – …, 2011 – science.sciencemag.org
Neuronal regulation: A mechanism for synaptic pruning during brain maturation by G Chechik, I Meilijson, E Ruppin – Neural computation, 1999 – MIT Press
Synaptic pruning in development: a computational account by G Chechik, I Meilijson, E Ruppin – Neural computation, 1998 – MIT Press
The complement system: an unexpected role in synaptic pruning during development and disease by AH Stephan, BA Barres… – Annual review of …, 2012 – annualreviews.org
Is schizophrenia due to excessive synaptic pruning in the prefrontal cortex? The Feinberg hypothesis revisited by MS Keshavan, S Anderson, JW Pettergrew – Journal of psychiatric research, 1994 – Elsevier
Progranulin deficiency promotes circuit-specific synaptic pruning by microglia via complement activation by H Lui, J Zhang, SR Makinson, MK Cahill, KW Kelley… – Cell, 2016 – Elsevier