The plastic spinal cord

You can’t teach an old spinal cord new tricks, or something like that. Up until recently (like the last ten or fifteen years), we had thought that the spinal cord was a fixed thing. It was the information highway of the body and its primary role was to receive, sort, and send information from the brain to the body and vice versa. That’s (thankfully) not the case. The truth, or at least something closer to the truth, is that the spinal cord is a lot like the brain. It can learn, think, and even act independently of the brain.

A lot of the work I do focuses on the brain, but my research is on the spinal cord. There’s surprisingly not a lot of difference between what makes up the brain and what makes up the spinal cord. There is white matter and there is grey matter. The brain and the spinal cord even share the same fluid, hence cerebrospinal fluid. So while it’s a good way to segment the anatomy, it’s not entirely correct to think of the spinal cord and the brain as two different things, sort of like different parts of the brain are still parts of the brain, so too is the spinal cord. Or at least that’s my feeling about it.

I realized recently that I haven’t talked about the spinal cord lately, so today I thought it would be fun to give a bit of a rundown on some of the cool things the spinal cord does. If you want a super detailed introduction to the spinal cord and all its weird quarks, I’ve got you covered there too with my “Know your spinal cord series” which is dozens of posts focusing on just about every aspect of the spinal cord I could think of! It’s probably one of the most comprehensive and accessible looks at what makes the spinal cord so awesome, so if you’re interested take a look!

We used to treat the spinal cord as a nerve, but it’s more like a long brain. The spinal cord is about the thickness of your pinky finger (or very tiny!), but it packs a lot of stuff. I mean it has to, the speed at which information travels from the foot, for example, to the brain is far too slow and you could seriously hurt yourself if the information had to travel all the way to the brain and back. How slow you may wonder? Well all things being equal it takes roughly 30-40 ms for information to travel from the common peroneal nerve to the brain (via electrical stimulation). I know this because I’ve done this type of study… a lot.

Keep in mind that’s one way, so at minimum it’s double the time for information to travel back from the brain to the muscles in the leg and even then you need to factor in the brain trying to process that information first. It can take (from a biological perspective) forever. In fact, the average human reflex speed is ~250-300 ms and if you’re super human, it’s still ~ 200 ms which is about 10 x longer than the speed of the typical reflex arc. If you were to step on a lego for example, your body could react and perform complex movements in ~30 ms from the stimulus (stepping on something), well before your brain even realizes what’s going on.

While pulling your foot away from a lego seems like a simple task, you’re really activating a whole bunch of different muscles to do that, there’s the muscle to pull the foot away obviously, but on the other side of the body your leg muscles need to contract to deal with the added weight or you would fall right over. So several muscles relax, others contract, and you (mostly) can keep your balance and you are aware of none of it until well after the fact. Sure your brain tries to convince you otherwise, but if you’ve ever been startled and jumped, you don’t have control over that reflex just like you don’t have control over the pain withdrawal reflex.

So the spinal cord can (and obviously does) act independently of the brain. It also processes a lot of information and sends it to the brain and from the brain to the muscles. The interesting thing is that the brain and muscles (and probably your organs too, although I don’t know that it’s been studied) speak different “languages.” The brain primarily uses lower frequencies to work, while the muscles prefer higher frequencies. The spinal cord is the translator of the body, converting messages from the brain and sending them to the muscles, taking information from the nerves, integrating it, translating it, and passing it on to the brain. It’s an incredibly complex and difficult to understand system. Not only does the spinal cord translate this information back and forth, it applies a non-linear (as in not a straight line) transformation to the data. It does things we just don’t understand.

There’s also evidence that the spinal cord can learn. Intuitively this may make sense if you’ve ever typed on a computer keyboard and didn’t need to figure out where the next key was (like I’m doing right… now). Or maybe you’re a swimmer and can zone out while you’re doing it. Maybe a piano player who doesn’t need to constantly think of how each finger is placed on the keys. While some of this is speculation, there has been several studies showing that the spinal cord can learn new things and I have plenty of reasons to think that is the case, as given in the examples above. I mean if you remember how hard it was to learn how to type to start and how much brain power it took, you can probably see why offloading that work to the spinal cord makes sense from the brains perspective.

The good part about this is that because we have ample evidence to show that the spinal cord is plastic like the brain, it can adapt. My research is with people who have spinal cord injury and the spinal cord can adapt to the damage just like the brain can adapt to a TBI or stroke. It doesn’t completely go away, but there is a demonstrable improvement. Especially when you do physical therapy or other tasks to help train the brain/spinal cord to deal with the change in information flow. It’s why people can recover some ability after injury and why time after injury is an important factor. You want to retrain the neurons (brain or spinal cord) as soon as possible.

At the end of the day I don’t like to think of the spinal cord as something different from the brain, but as part of the brain. The tail of the brain if you will. More people are understanding that the spinal cord isn’t a fixed nerve, which is good for a whole lot of reasons. A better understanding of the spinal cord won’t just benefit people who have had spinal cord injury, there are other types of diseases that affect the spinal cord, and more importantly a clearer understanding of its function will help us better understand the brain.

I’m excited that there has been a shift in the last year or two towards more research on just how the spinal cord works and spinal cord injury in general. I think it will benefit anyone dealing with the brain, spinal cord, or the body. There’s been a lot of new discoveries coming and I’m hopeful that I can contribute to some of that. In the meantime I hope that by writing stuff like this, others will be interested and even if you don’t want to do research, it’s always fun to learn something new!