On the prefrontal cortex and abuse

Adulthood is often thought of as the point where you’re done developing. Most states for example don’t allow anyone under 21 to drink because that was where we drew the line, but we allow people as young as 18 (here in the US) to join the military, vote, etc. You may think that this would be roughly where we stop developing and that would explain the somewhat artificial line we’ve drawn. The truth is much stranger than that and when it comes to the brain you don’t develop evenly.

If every abuse and trauma that occurred to a person left a physical scar, even the people who know me best wouldn’t be able to recognize me. I grew up in an abusive home, well homes really. I moved around a lot, got passed around between family members who all equally really didn’t want anything to do with me, and generally didn’t have a good childhood. You could count on one hand days between bloody noses for example. The truth is trauma leaves invisible scars. We’ve seen them in MRI scans of the brain, in the way the brain develops, and in the life-long effects trauma has. There’s a line of reasoning that goes like this; if you’re abused you have a higher risk of abusing your kids/family/insert whatever you like here. That’s demonstrably false by looking at the statistics. I mean personally I’m more likely to hurt myself than anyone else, but there’s also an odd quark in neuroscience which helps explain this as well.

The brain tends to develop back to front. MRI scans have shown that areas of the brain develop at different rates. This is important because — from our current understanding of the brain, which isn’t great mind you — we believe that the prefrontal cortex, or the front of your brain, controls your so-called “executive functions.” That covers things like, but not limited to; right vs. wrong (inhibiting inappropriate behavior), long-term strategies, planning, impulse control, attention, problem solving, and foreseeing consequences. Basically all the “stuff” that makes you behave the way you do. Which also helps explain why teenagers act so (broadly speaking) reckless.

Of all the parts of your brain, we have ample evidence to suggest the prefrontal cortex develops the very last. MRI studies have shown that white matter in teens is far lower than in older adults, but this increases as a teenager gets older. White matter is the connective bits in the brain, it’s “white” because of the coating that goes around the connections, called myelin. Myelin is a fatty tissue that surround neurons and it does a lot, but you can think of it as speeding up signal transfer. Imagine it like this, if a neuron was an extension cord, the myelin would be the thick plastic protecting the wire and keeping the electricity inside. This increases the speed of the signal so the more myelination that a neuron has the faster the signal travels.

Not only do the number of connections get fine tuned as we get older (synaptic pruning), so too does myelin thickness. So the prefrontal cortex develops last — or again this is our current understanding of the brain, which has evolved considerably over the years — and we have a pretty good idea about how long this development lasts, even if we cannot be completely sure of the entire list of behaviors the prefrontal cortex controls. So just how long does it take for the prefrontal cortex to develop? Well that depends somewhat on the person, but currently that age sits around 25 years old. Yep, you’re allowed to have a mid-mid life crisis and you’ve only just developed.

Here’s the thing though, we have a pretty good idea that the prefrontal cortex is in charge of all the stuff I just listed and we know pretty well that development finishes around the 25 year mark, and that’s a good thing. In my opinion it’s what makes us so resilient, humans in general sure, but I mean specifically childhood abuse survivors. The fact that the bit of the brain that helps you essentially be kind (or at least understand consequences and what not) doesn’t develop until well after you’ve hit societies “adulthood” marker gives you a chance. For once biology is on our side and when I learnt this it made me feel slightly better.

On one hand it’s frustrating that the prefrontal cortex, if the (from our current understanding) sole purveyor of self-control and other important functions that make it possible for us to understand our actions, takes so long to develop. I can’t think of a time in my life where having well developed executive action wouldn’t come in handy. It also makes the latest ruling from SCOTUS on lifetime sentences for juveniles excessively cruel and very much anti-science. Not surprising since the court was packed by the GOP who is famously anti-science and pro-cruelty, but that’s a whole other post for another time.

On the other hand, the fact that the prefrontal cortex develops so late in life is a blessing. At 18 I was serving my country in the Marine Corps, far away from my family, but at 25 I was already years back into civilian life trying to adapt. While other parts of my brain development were firmly and irrevocably shaped by my childhood, a childhood where I had no control, my prefrontal cortex, had no such limitations. My prefrontal cortex development was shaped by me. While my life circumstances have, and would always, play a role in that development I was far removed from the abusive situation I was in during my adolescence.

Thus my prefrontal cortex development was a product of some of, if not all of, the choices I got to make. For once my neurodevelopment was in my control and I like that idea a lot. We don’t get to chose our birth circumstances and in a lot of ways we are never given the opportunity to outgrow the shackles placed on us, but there is a difference, however small, in having no control and having some control.

It’s also one of the reasons (in my opinion mind you) that I think people who are raised in abusive situations don’t always go on to hurt others. Yes, there is a cycle of violence that oftentimes is perpetuated, but we can’t necessarily blame that on growing up in that environment. I like to think that this late development is what gave me the ability to be different from my family. My family and I know right from wrong, but they made the choice to continue the cycle, I made the choice to end it. So did my Uncle! Neither of us got away unscathed and even though I think my Uncle was a far better man than I could ever be, we still both decided to be good people. We still suffered from events in our lives and we even both tried to kill ourselves, the difference is, he succeeded. Semi-related side note: I don’t care who you are, guns are not something people should be able to buy so readily.

The overarching point is simply that with late development of the bit of our brain that controls our executive functions, we’re not exactly a product of our childhood environment, we can be more. Sure, there’s a certain amount of luck involved and I’m not saying childhood effects of trauma don’t leave a lifelong scar, because they definitely do. What I’m saying is the nice part about the late development of the prefrontal cortex is that it gives us a chance, even if we weren’t born with one.

I don’t know, maybe I’m prescribing feelings to biology when biology doesn’t particularly care, but it helps me sleep at night knowing that my family didn’t get to shape some of the more important parts of me. For better or worse, I got to do that. For someone who didn’t get much control over his early life, that means something, even if it doesn’t mean a damn thing to biology.

I don’t like making claims without some evidence for them, these are just a few of the sources for the developing brain if you want to know more. While most and/or all of this was opinion, it was an opinion based on the way we develop and there’s a bit of science there.

Sources:

Arain, Mariam et al. “Maturation of the adolescent brain.” Neuropsychiatric disease and treatment vol. 9 (2013): 449-61. doi:10.2147/NDT.S39776

Shaw, GA, Dupree, JL, Neigh, GN. “Adolescent maturation of the prefrontal cortex: Role of stress and sex in shaping adult risk for compromise.” Genes, Brain and Behavior. 2020; 19:e12626. doi: https://doi.org/10.1111/gbb.12626

Miller, Daniel J., et al. “Prolonged myelination in human neocortical evolution.” Proceedings of the National Academy of Sciences 109.41 (2012): 16480-16485. doi: 10.1073/pnas.1117943109

Forbes, Thomas A., and Vittorio Gallo. “All wrapped up: Environmental effects on myelination.” Trends in neurosciences 40.9 (2017): 572-587. doi: 10.1016/j.tins.2017.06.009