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Mar 9, 2010

The Science of Science Fiction


The brain is molecules all the way down.
In what is now probably the most profitable science fiction story of all time (Avatar), the protagonist transfers his mind to a new body. Mind transfer has become a staple plot element in science fiction: human to chimp, human to robot, robot to human, alien to human, human to alien-human hybrid...have mind, will transfer.

From time to time it is fun to take stock of the relationship between our science fiction plot devices and real science. The Dick Tracy science fiction wrist phone of the early 1940s is no longer a gee-wiz science fiction plot element. How are things looking on the mind transfer front? Luc Reid recently tried his hand at comparing the reality of brain science to science fiction depictions of mind transfer.

While trying to explain the complexity of biological brains, Reid describes the mind-generating machinery of our brains as being composed of "two major systems". Reid's approach to explaining how a brain makes a mind is rather contorted and it made me think of Paul Churchland's book "The Engine of Reason, The Seat of the Soul". In that book, Churchland was doing some rear-guard maneuvering to convince philosophical mind/brain dualists that we need not imagine any non-physical components of mind. As an example of how some "explanations" of phenomena can be too complex, Churchland pointed to Betty Crocker's account of how microwave cooking works.

jumping minds
According to Betty Crocker, microwaves cause 1) water molecules in food to vibrate which causes 2) friction which makes food hot. Similarly, Reid's two step account of brain function involves both 1) neural networks and 2) chemical systems. Betty Crocker imagined that making hot food involves something more than vibrating molecules and Reid imagines that our minds are more than neural networks. What more? According to Betty Crocker vibrating molecules is not enough to make hot food because, in addition, you need heat. According to Reid neural networks are not enough to make a mind because, in addition, you need chemicals. Reid seems to imagine that neural networks are little electrical circuits: "our mind is much larger than our brain, encompassing a wide variety of sensations and emotions that, while they trigger neural activity, are at least as chemical as they are electrical." Similarly, Betty Crocker went out of her way to "explain" to us that microwave cooking is more than just making more molecular motion in our food.

source
The alternative view of the mind is that, "our mind is the activity of our brain". Just as heat in food is molecular motion, neural networks in our brains are chemicals. Sensations and emotions do not trigger neural activity, they are the activity of our neural networks. There is a famous joke in cosmology about it being "Turtles all the way down" and in the case of neural networks in our brains, it is molecules all the way down. Neuroscientists do not study neural networks on Mondays and then take up the task of studying brain chemicals on Tuesdays. The study of neural networks in the brain is fully integrated with and dependent upon the study of brain chemistry. Our neural networks are chemical systems.

In The Start of Eternity, the protagonist, Gohrlay, gets to learn about the advanced brain science that makes mind transfer possible. At no point does she pause and exclaim, "Wait, what about the chemicals?" The story assumes that hard-working scientists have developed the technology needed to scan the structure of a human brain and translate the neural networks into the form of functionally equivalent positronic brain circuits inside a robot. Rest assured, all of the brain chemistry has been taken into account.

Update: Foundation of Eternity
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3 comments:

  1. Hi John,

    This won't come as any shock, but I have to disagree that the chemicals are part of the neural network and therefore already taken into account. The neural network is a network of neurons (hence the name, of course), which as you may know are brain cells that make connections of varying strengths with other neurons, between which electrical impulses pass across junctions called synapses. All of the activity apart from growth and degradation occurs as electrical impulses, neuron to neuron. The reason the chemical system is another entire consideration is that it it stimulates neurons chemically in ways that those neurons would not otherwise have any way to be stimulated. I'm puzzled at why you would characterize our neural activity as not being essentially electrical in nature. Can you elaborate?

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  2. "electrical impulses pass across junctions called synapses" <-- This text book describes the fact that most synapses are not electrical. The vast majority of synapses in neural networks are chemical synapses. "electrical impulses, neuron to neuron" <-- very few electrical impulses pass between neurons. "Electrical impulse" usually means an action potential. Within neural networks, most action potentials travel along the surface of an individual cell. Chemicals (neurotransmitters) carry the signals between neurons. "essentially electrical in nature" <-- I'm not sure what you mean by "essentially electrical". Yes there are changing membrane potentials in neurons, but what is a membrane? It is a thin layer of chemicals. What makes the electrical signals on neurons? Charges ions moving through ion channels. What are ion channels? Chemicals, specifically, proteins. There is no electrical signal in any neuron without chemicals. So what does "essentially electrical" mean? It means chemicals that make up neuronal membranes allow charged ions to move across and along the membranes. So I'd characterize our neural network activity as essentially chemical. Part of the chemistry of neurons is allowing sodium and potassium ions to move through ion channels and produce membrane potential changes (action potentials). Action potentials travel along axons and when they reach synapses they trigger chemical neurotransmitters to be released which cross the synaptic cleft to the next neuron. If you ignore the details of brain chemistry then that leads making a false distinction between the neural networks and the chemicals.

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    Replies
    1. In my comment above (six years ago!) there is a typo where it says "Charges ions moving through ion channels." It should be "Charged ions moving through ion channels."

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