Welcome back to Birdbrained Science! Last time, we touched on the ‘bird’ aspect with migration and today, we’ll cover some brain stuff — let’s talk about pruning.
I think there are some delightful comparisons to be made between plants and the brain (for example, dendrites, which are shaped like tree branches and named accordingly), and one of these comparisons is the process of pruning. In plants, this process involves removing dead or dying parts so that a plant can focus its energy on strengthening its healthy parts. Brains also undergo pruning, although in this case it’s not branches that get pruned — rather, synapses get pruned. A synapse is the place where different neurons communicate with one another — in other words, the place where two different neurons can form connections with each other.
We are born with an absolutely absurd number of neurons — around 100 billion at birth — which is 15% more than the number we get as an adult. Since neurons can have multiple synapses, this means that at birth, we have a high number of synapses alongside our many neurons. Somehow, we still gain more — for the first few years of our lives, our brains just keep making synapses, opening up infinite potential for connections to be made. As Harvard neuroscientist Jeff Lichtman puts it, “…you start out wired up for every possible contingency.”
Around adolescence, however, that trend stops; instead, synaptic pruning begins. Although the exact process isn’t fully understood yet, microglia (brain cells that eat debris and damaged and diseased cells in the brain) appear to play an important role. They seem tuned into the happenings of synapses and neurons, wrapping around the neurons that are activated more often and have also been observed swallowing synaptic material.
However it happens, we know that once synaptic pruning occurs, some neuronal connections are lost forever. Pruned brains generally seem to be less flexible. This is why it’s much easier to learn a language before puberty; the connections to learn new languages are still open then.
But if synaptic pruning leads to the loss of cool things like the ability to easily learn new languages, why do our brains prune synapses? Similarly to plants, it’s thought that this kind of pruning allows the brain to redirect its resources towards strengthening and specializing important connections, rather than feeding underutilized ones. Studies have shown that pruning may lead to improved task performance. Additionally, lack of synaptic pruning might be bad for you — impaired synaptic pruning may be linked to several disorders such as autism, schizophrenia and epilepsy.
“What you’re left with is a narrow system,” Lichtman explains, on the brain post-pruning. “But it’s tuned exactly to the world you found yourself in.”
While it sucks to cut old connections, it ultimately may be for the best. It’s not easy to function if you’re constantly holding onto every connection you’ve ever made, and it can take your energy away from more important ones.
So if our brains (and plants!) are anything to go by, it’s okay to let go of old connections and just focus on the ones that matter the most as you mature. Not every connection is always going to serve you, and you are simply not built to give to every connection forever.