The Atheist's Guide to Reality_ Enjoying Life Without Illusions - Alex Rosenberg [83]
Feeling a bit baffled? Read on.
SEA SLUGS, RATS, AND HUMANS—
IT’S ALL THE SAME TO NEUROSCIENCE
Swell. Then how does the brain store information if not in thoughts about stuff? Where are all those beliefs that enable us to get around the world to be found in the brain? And what about the wants, desires, hopes, and fears we have that team up with our beliefs to drive our behavior? How does the brain store them? Neuroscience is beginning to answer these questions. We can sketch some of the answer in the work that won Eric Kandel the Nobel Prize in Physiology or Medicine. The answer shows how completely wrong consciousness is when it comes to how the brain works. Indeed, it shows how wrong consciousness is when it comes to how consciousness works.
Kandel started out by discovering how the sea slug learns things. The sea slug is a pretty big snail without a shell. It can grow to more than 50 centimeters, or a couple of feet, in length. More important, it has a small number of rather large neurons that are easy to identify and easy to monitor right down to the molecular processes that go on inside these neurons and in between them.
Like Pavlov’s dogs, only more easily, the sea slug can be subjected to conditioning experiments. Recall Pavlov’s famous experiment: by presenting a dish of meat (the unconditioned stimulus) to dogs and ringing a bell at the same time over and over again, he was able to get them to salivate at the sound of the bell without the meat. The sound of the bell was the “conditioned” stimulus. Similarly, the sea slug can learn to withdraw its gills and its siphon from a conditioned stimulus. For example, combine a harmless electrical stimulus (the conditioned stimulus) on one nerve with a painful stimulus (the unconditioned stimulus) on another nearby nerve. The sea slug will soon respond to the painless electrical stimulus alone the way it originally responds to the combined painful and painless stimuli. It will withdraw its gill and siphon. Voilà! Learning by classical conditioning.
The real beauty of sea slug training is that Kandel was then able to see how the conditioning changed the neurons.
The changes are broadly of two types, depending on the conditioning experiments. Pair the unconditioned stimulus (the painful shock) and the conditioned stimulus (the harmless one) a few times. Then the sea slug will respond to the harmless stimulation alone once or twice, but will soon cease to respond to it. Pair the unconditioned and the conditioned stimulus several times, and the sea slug will continue to respond to the unconditioned stimulus—the harmless one—for a long time. Kandel discovered the source of the difference. A little training releases proteins that open up the channels, the synapses, between the neurons, so it is easier for molecules of calcium, potassium, sodium, and chloride to move through their gaps, carrying electrical charges between the neurons. This produces short-term memory in the sea slug. Training over a longer period does the same thing, but also stimulates genes in the neurons’ nuclei to build new synapses that last for some time. The more synapses, the longer the conditioning lasts. The result is long-term memory in the sea slug.
The genes in the nuclei of each cell that control its activities are called somatic genes, in contrast with the germ-line genes in sperm and eggs, which transmit hereditary information. Both kinds of genes contain the same information, since the order of DNA molecules in each of them is the same. Somatic genes are copied from germ-line genes during embryonic development.
Now, the sea slug does not actually learn and store any information that could be expressed in thoughts about stimuli. It doesn’t have the thought, “Uh oh, painless electrical stimulation in neuron 1. That means painful stimuli is coming in neuron 2, so it’s time to pull back the