I went hiking this weekend, and I saw a lizard. I was excited because it looked like this was the kind of creature that could regrow its tail as a defense mechanism. I thought about regrowing limbs, I thought about the heat from the sun, and I thought about how happy I am to be human and not a lizard with a blue tail.
Typically, we think without thinking about it. In fact, many find it hard not to think. That’s why meditation requires serious practice. But, for something that takes place so quickly and routinely, there are a lot of intermediate steps we don’t even have time to consider.
Thought, as it turns out, is not instantaneous (even though it feels like it when you decide that yes, you will have another chocolate), as Carl Zimmer explores. In fact, most signals in the body function analogously to wires or other electronics. Even though listening and comprehending your friend’s story over the phone feels immediate, it actually takes a fraction of a second for his or her voice to travel across the airwaves.
Believe it or not, the invention of the telegraph in 1844 inspired our first model of how nerves work. When it took a split second for messages to be transferred across the country, it seemed to be just as simultaneous as thoughts or feelings perceived in different regions of the body. In 1850, German scientist Hermann von Helmholtz used frog legs and wires to measure the time it took the electric signal to travel through the dead animal. It turned out to be roughly a tenth of a second. Additionally, Helmholtz tested to see how long it took people to feel different shocks on different parts of the body. Though it took longer to feel discomforts on the extremities than on the base of the back, he found that it also took about a tenth of second.
This discovery led the earliest neuroscientists to believe that nerves send signals to the brain, and that our brains analyze them further. These signals, called neurotransmitters, are received by the ends of axons. If the neurotransmitters are like baseballs, axons function kind of like mitts. Axons communicate with neurons to tell them how to interpret these different signals.
Complicating the story, of course, is the fact that regions of neurons our brains process different things. For example, the part of our brain that processes sight is called the thalamus, which then sends another signal back to the visual cortex in the back of the brain. So in reality, these signals may bounce around several different parts of the brain before we really form a complete thought about what they mean.
This means that different processes come at different speeds. Sound is processed almost immediately — hearing a loud noise will trigger an instinctual response in just .05 seconds. Sight happens relatively quickly too. However, our brains purposefully slow down some receptors so that our consciousness doesn’t go into sensory overload.
Taking a big step back, our thoughts and decisions come down to a lot of different molecules (and a slight current that comes with a varying charge gradient). These changes can be traced down more or less to chemical reactions. And, if you consider the basic structure of our nerves, we're not that much more than chemistry with a little electric current.
The technical aspects of neuroscience interest me greatly, but the philosophical implications of these processes compel me more. If it turns out that our thoughts and musings come down to a few signals here or there, what does that mean about some of the more profound human experiences? What about love? What about grief? What about poetry, and the inexplicable beauty of a small lizard in the middle of the woods on a hot summer day?
I like to think I — my essential “Katherine-ness” — is more than just some grey matter influenced by different compounds. But at the end of the day, there’s something rather comforting in the idea that all the overwhelming experiences and thoughts we have just come down to a few simple chemical reactions and interaction.