Consider the following thought experiment: Imagine you have kidney disease and receive a kidney transplant. Are you still yourself?
Imagine you lose a leg and receive a prosthesis. Not the archaic models of today, but a prosthesis that functions just as well as a natural leg and looks like one, too. Are you still yourself?
How about a mechanical heart or an artificial eye with 20/20 vision? Would you still feel like yourself?
I guess I would. Sooner or later, I would surely welcome organs that perform their duties better than my own. If the replacement parts worked well, I would feel like myself, or, if anything, I would feel better, but nevertheless myself.
In our thought experiment, we could go on and on until we reach the brain.
The brain consists of several parts. The brainstem controls vital functions like heart rate and breathing rate. A sophisticated computer could theoretically take over.
The cerebellum coordinates movement, which is also something that could potentially be outsourced to a computer in the future without eliminating ourselves.
But now it gets trickier. In the limbic system sit our emotions, and mostly in the outer brain, the cortex, are intellectual functions and memories.
Brain memories are not like saving computer data because they are not just data, but data associated with emotions.
Here we get to the core of ourselves: memories associated with emotions.
Saved data alone isn't the self. Information saved on a hard disk does not have a personality, and thus no self. Even if one were to download all the data circulating on the Internet into one computer, it would still only be data, with no self.
Likewise, emotions without memory are just reflexes, not a self.
Consider another thought experiment: imagine a person with zero memory capacity. They never know what happened in the previous second. They also do not know what happened in the previous one-hundredth or one-thousandth of a second. In that case, there is no personality, no self. There might be a scream in response to pain, but how intensely is pain felt if it is forgotten the moment it happens?
So, our sense of self is just memories associated with emotions, or emotions associated with memories.
Now think further. There are diseases that erode and erase our memories. Alzheimer's does a thorough job of this, and other forms of dementia achieve it, too. I am less certain about illnesses that destroy feelings, because feelings would encompass not just anger, love, and appetite—whether sexual or for food—but also pain. This includes not just the diabetic loss of pain sensation in the extremities, but also conditions where nerve signals fail to arrive in the brain to be perceived.
Anesthetics, of course, interfere with feeling anything, including pain, and they eliminate awareness. A coma has a similar effect.
The details may be a bit vague here, but they might not be that important. An ideology needs only a general idea.
Neurons from anywhere in the body send signals to the forebrain, specifically the thalamus. Neurons conduct signals electrically, but they are not directly connected to the thalamus and other nearby brain structures. Rather, at the synapses, transmission is switched to chemical neurotransmitters. All anesthetics interfere with signal transmission via neurotransmitters, not only between peripheral neurons and the thalamus but throughout the entire brain. The result is a total loss of sensation, awareness, and the storage of perceptual data.
So, here we are at the basics of what we are: a soup of neurochemicals in our brains that is responsible for almost everything we feel and think. There aren't even terribly many neurotransmitters—just over 100, with glutamate and GABA being the most common.
But you get the idea that we really are just a biochemical porridge, with chemicals connecting here and there upon electrical stimulation. It is not very metaphysical, and too down-to-earth to serve as a foundation for religions. We aren't much, just circulating chemicals that are so easily modified by medications. Nevertheless, pain, or torture, feels so much more meaningful than just a little bit of chemistry.
All of this can seem so senseless. One might wish for a deep sleep, or at least some pain relief to tilt this brain soup into a more pleasurable state, and simply turn off the mind's electricity.
