The complexity of biology
Why couldn’t things be simple? Maybe you would take a measurement and have the correct value every time. Or you would perform an experiment and get the same result no matter what. The human body is an amazing feat of engineering by evolution. It’s layer upon layer of stuff that all work together to do the thing that needs to happen. The fact that it works at all is amazing, it’s like throwing a bunch of computers into a room, shaking it, and out comes a fully working robot that’s more advanced than anything you’ve seen.
We rely on numbers to squeeze out useful information from biology. Especially the stuff I do. EEG is measured in microvolts, a tiny, tiny, measurement and if it weren’t for the fact that EEG has been verified time and time again as a useful way to measure brain activity I wouldn’t believe it could be done. I still feel like there’s some sort of magic that happens that gives us the solution and I worry that the answer it provides isn’t always the truth. Of course that’s why we use the dark forces of statistics to tell us if our answer has a meaning or not… but there’s pitfalls there too.
Long story short (a new thing around here I’m sure) biology is complex and even when we eliminate all the other variables we have and focus on one single thing, even the simplest of things, it isn’t REALLY just one thing. It’s a complex biological rube goldberg machine that we set off. In the body some of the “simplest” things we can study are reflexes. The H-reflex for example is considered a two neuron reflex arc, one traveling to the spinal cord and one traveling back to the muscle it activates. In reality that is a oversimplification and it triggers a cascade of effects in the spinal cord involving hundreds (if not more) neurons. We simplify it because all the other stuff doesn’t matter for the H-reflex, the machine cranks away and gives us a repeatable output from the same input, it’s a beautiful thing and is why the h-reflex is probably one of the most studied reflexes in the body.
Needless to say when your doing research that requires you to estimate that complex machinery behind the input and output, it’s hard. There’s a lot of what-if’s, but what’s really frustrating is that for every one answer we find, there are 20 questions that come with it. I’ve been having a discussion with my Co-PI (sad face) about the origin of somatosensory evoked potentials (SSEP’s), which are just the brain’s response to an electrical stimulus (you can evoke them other ways, but that’s the way we do it in the lab), technically they are sensory responses or at least that’s what everyone keeps saying, but you need to evoke a motor response to cause them and I was frustratingly trying to answer the why. Why do we need a motor response if they are a sensory potential?
At first my guess was that the motor response was a reflex arc or that we were activating the muscle by virtue of stimulus and the intensity required to cause an SSEP just happens to be above motor threshold and it works for researchers because we can use the motor response as a good indicator that we’re at the correct placement. Interestingly enough biology works in our favor for a lot of the stuff we do, finding landmarks on the spinal column for example is surprisingly easy and it didn’t have to be that way. So on one hand I would believe it if nature just worked in our favor.
In any case, I’ve got a lot of digging to do now. It’s been a long, long, long day, which is why the post is coming at the end of the day and not the start! We had an early morning experiment where I tried something new, found something cool, and now we have 20 more questions that we need to find answers to and even though today marked the official end of the experiments for this paradigm, because I’ve found something interesting, we’re going to do more. Statistics is a pain, trust me on that.
With that it’s time for me to do some digging, but hey if you know the answer to why motor responses are required for SSEP’s feel free to share. I don’t know everything and google hasn’t been the friendliest with regards to the question.