Why Consciousness Makes Our Heads Hurt
Saints and Sceptics
At the Centre for Neural Research at New York University, Joseph LeDoux has carried out impressive research on how traumatic memories are formed, stored, and retrieved in the brain. LeDoux is perhaps best known for his experiments on rats, which were trained to associate certain stimuli, like musical notes, with unpleasant sensations, like electric shocks. After a while the rats learned to fear the sound of certain musical notes. Their initial response was a “freeze” reaction – an innate reflex, which is useful for avoiding predators in the wild (but not for evading neuroscientists armed with tiny tasers in research facilities).
LeDoux’s research team discovered that rats with damage to the lateral nucleus in the amygdala did not learn to freeze. So this part of the brain is obviously very important in retaining traumatic memories. By conducting experiments like this, LeDoux’s lab has learned how to map the “fear system” in the brain. These researchers contend that physiological responses, like freezing, occur first; only then do we feel the subjective sensation of fear. This is important for developing treatment for people suffering emotional disorders; their extreme physiological reactions are often involuntary, and we need to recognise this if we are to help them overcome their symptoms.
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Now in order to be consciously fearful you have to have a sufficiently complex kind of brain. But as complex as a rat’s brain is, it is not an exact match for the human brain. So here’s the crunch. What does the rat experience when it has a “freeze” reaction? No matter how much detail we gather about the workings of the rat’s brain, we will never actually know what it is like to be a rat. We can only make imaginative guesses; and there are some animal experiences we cannot even speculate about. Eric Kandel won a Nobel Prize for his experiments on Aplysia californica – a type of sea snail. When sprayed with a jet of water Aplysia withdraws inside its mantle; but if it is sprayed repeatedly it learns to disregard the stimulus.
This process of learning is called “habituation”; the sea snail ‘learns’ that the jet of water causes no harm, and ‘learns’ to ignore it. Kandel then found a way of “sensitising” Aplysia. He gave it electric shocks whilst spraying it; eventually, the snails withdrew at the slightest touch. Kandel’s research was not focused on creating paranoid sea-snails. Chemicals known as neuro-transmitters carry information through the brain; Kandel showed that chemically neutralising the CREB protein effects the production of certain neuro-transmitters, and this prevents Aplysia from becoming sensitised.
Experiments with a wide variety of animals, sensitising them and habituating them to various stumuli, confirmed that CREB is the master switch in the formation of long term memory. When we remove the CREB protein animals can no longer form “memories” – they no longer become sensitised to various stimuli. But Aplysia doesn’t “remember” events in the sense that humans recall the past. So do sea-snails experience anything at all, or do they act and react like machines or computers? And if they have any conscious experiences, what are those experiences like?