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.
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?
Neuro-science can describe animals as a system of causal inputs, provided by or in the form of representation, that produce certain casual outputs. But this description of inputs and outputs does not describe intrinsic, subjective feelings. We can predict and describe neural events and the behaviour these cause. But experience, by common consensus, is out of bounds. Behaviour and neural events are open to “third person, public” observation. We can only describe and understand emotions like fear and anger in the first person – “from the inside”, as it were. If we could describe every physical fact about the rat’s brain in every detail, we would still not have a description of what the rat experiences. There are facts about animals that are not physical facts – facts about “what it is like”.
It does not matter what concepts we gain, what we imagine, or how much data we gather. We are forever barred from another animal’s rich world of experience. There are some things which we will never know; and if we do not know exactly what the rat is experiencing, we simply cannot explain it. This should lead us to reconsider our own world of experience. In every conscious moment we are aware of numerous, irreducibly different states of affairs. We can be simultaneously aware of colours pains, smells, tastes, beliefs, decisions and desires.
The brain processes a scene when populations of sensory cells cut it into chunks of information that can processed by millions and millions of cells deep in the cortex. Yet we do not experience numerous interacting parts; instead we experience one coherent image. This image is so rich that one artist could render one scene in a thousand styles and still not exhaust everything that he had been aware of. Our emotions are deeper still: ecstasy and regret, wishing and hoping, can barely be communicated in music or art; poets and philosophers can enlighten, but never exhaust, the meaning of emotion.
The qualities that characterise experience (like sensation, meaning and purpose) are not the properties that characterise physical parts (like mass and energy). It is not even intelligible to suggest that feelings can be explicated in equations. We can dissect nerves and tissue into their various spatial parts; we can detect inputs and outputs. Yet, while we can direct our attention to one part of our stream of consciousness, we cannot dissect conscious experience into parts or particles. To argue that consciousness is physical is like arguing the sun is really a prime number.
Not only do we have a unified conscious awareness of numerous facts; we also seem to be selves that endure through time. We do not merely recall the fact that a certain event happened; we remember our experiences from our own subjective perspective. Every memory includes a reference to the “I” who is remembering. This unity of our psychological lives is best explained if we are enduring selves: what a previous era would have called a “soul”.
The idea that we are enduring, conscious beings is not a hypothesis that attempts to account for scientific observations. It merely reports what we are directly acquainted with when we reflected on our own experience. We just seem to be enduring, rational selves. If we are mistaken about the deep matters of the self, it is difficult to see how we could depend on any other observation. Materialism struggles to account for our first person experience because it cannot allow the non-physical to exist: consciousness remains a puzzle and a mystery on this worldview. Whether we like it or not, unless we abandon scientistic materialism of our age we will never take the measure of what is truly human: our very souls.