Today I finished reading Robert Sapolsky's book, Determined: A Science of Life Without Free Will, by making my way through a fascinating appendix that, in 24 pages, gives an overview of how the brain works.
It was a mind-blowing description of how, in broad strokes, the mind arises from goings-on in the brain. I'm not going to attempt to repeat what Sapolsky had to say, aside from sharing one of the illustrations in the appendix along with a brief quotation.
What neurons do is talk to each other, cause each other to get excited. At one end of a neuron are its metaphorical ears, specialized processes that receive information from another neuron. At the other end are the processes that are the mouth, that communicate with the next neuron in line.
The ears, the inputs are called dendrites. The output begins with a single long cable called an axon, which then ramifies into axonal endings -- these axon terminals are the mouths... The axon terminals connect to the spines on the branches of the next neuron in line.
Thus, a neuron's dendritic ears are informed that the neuron behind it is excited. The flow of information then sweeps from the dendrites to the cell body to the axon to the axon terminals, and is then passed on to the next neuron.
The illustration shows that there isn't a direct connection between the dendrite (ear) and the axon (mouth). That gap is a synapse. It is bridged by neurotransmitters, chemical messengers. I found a charming Neuroscience for Kids page that looks like it was made in the early days of the Internet. It has a quote at the bottom:
"You are your synapses. They are who you are."
--- Joseph LeDoux, 2002 (in Synaptic Self)
So true. That's the message in Sapolsky's appendix that comes through loud and clear, as it does in the rest of his book.
Most of us have the sensation that we are something ethereal, soul-like. Our thoughts, emotions, desires, hopes, fears, perceptions, and so much else feel like they're being fashioned from immaterial consciousness.
But the neuroscientific truth is that our 100 billion or so neurons, each of which has thousands of connections to other neurons, producing what's been called the most complex entity in the universe, the human brain, is made of meat, as is the rest of our body.
I already knew this. However, reading the readable appendix brought it home to me in a stronger fashion than I'd ever experienced before. This doesn't take away from the marvelous capabilities of the human brain.
It simply places us firmly in the natural world inhabited by every other type of living creature. As Sapolsky says in his book, a flatworm with just a few hundred neurons learns in the same way as we do with our hundred billion or so neurons.
I don't find this at all disturbing. I find it exhilarating. We are part of the physical universe, not something separate from it. That oneness is an inspiring scientific fact.