Chapter Six. The Amazing Brain
So much has been discovered about the brain in the last two or three decades it is hardly surprising that many feel that the last bastion of pre-scientific religious belief, the soul, is about to fall. Conscious intelligence is ‘nothing but the interaction of nerve cells and the molecules associated with them’ writes Professor Paul Churchland. ‘The Astonishing Hypothesis is that “You”, your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules’, claims Francis Crick in similar vein. He throws in for good measure a quotation from the old Catholic penny catechism. ‘The soul is a living being without a body, having reason and free will’. Small wonder that reductionist scientists want to do battle with that. According to Daniel Dennett there is no little man inside your head watching, as if on a cinema screen, your experience of your experiences, the homunculus in the Cartesian theatre as he puts it. Science has discovered that the brain is a parallel computer. All the time it is comparing and judging alternative explanations for what we sense. You see a shape flying past the window. One neuronal pathway in the brain suggests it is a bird. Another a stone thrown by an angry writer whose book you recently reviewed in somewhat negative fashion. Another possibility is that it is a surfacing memory of a cricket ball Pietersen recently hit at Lords right into your swiftly vacated seat. Quick as thought, and unconsciously, the brain compares these possibilities in terms of evolutionary advantage and selects one, the only one that reaches consciousness. It’s a bird.
Consciousness is not evidence for a soul directly infused into the body by God. It is an evolutionary device that developed to bypass all those tedious sequential comparisons, supremely useful when it came to taking instantaneous and immediate action in case of encountering a hostile predator, or, predatory yourself, working out the cunning hiding place of your desired victim. It is a supreme tool of agency, rather like the red light that comes on in your central heating system to indicate that the thermostat needs turning down, but a self-regulating red light so sophisticatedly self-reporting it knows it’s a red light and knows whatever it’s indicating to itself means, an instrument of negotiation far, far more efficient in an unpredictable world. Our sense of self, that we are somehow more than the sum of the processes of our bodies, ineffable beings possessed of free will, is, according to Dennett, what computer scientists call a user illusion.
I have no quarrel with any of this. I don’t think that the soul is a living being without a body at all. It is, exactly, ‘the behavior of a vast assembly of nerve cells and their associated molecules’. I just think these writers have not thought enough about the various possibilities of what that might mean. How easily those words ‘behavior’ and ‘nothing but’ and ‘computer’ slip from the pen. The one thing they don’t do, unlike their brains, is compare and judge, but, in my view, interpret these findings solely within the confines of a particularly limited and unquestioned paradigm. I want to escape from that paradigm, or at least question it. The strangest thing about human beings is that we have universal brains trapped in local circumstances. You can’t avoid asking yourself the question where do I get food. But you can’t avoid asking whether you think God exists or not either, for we all have to decide whether to get up on Sunday morning to go to church or whether to stay in bed. But we can only start to ask questions about the universal and ultimate features of reality that we cannot know by considering local things that we do know. We are surrounded by things, so our first and foundational question has to be: what is a thing and how do we know it?
Many scientists still think, though often unconsciously, within a philosophical paradigm inherited from Locke and Hume. Locke’s starting points are two, so obviously the case, he thinks, that he takes them for granted. One is that all our knowledge comes through sense impressions, there are no innate ideas in the brain. Sense data impress themselves on the brain, he said, ‘as a signet ring makes an impression in wax.’ His other founding principle is that our sense that we know whole things – look, there’s a tree we say – is an illusion. We only know different aspects of things through our different senses which the brain ‘associates’, to use his word. What we actually see when we look at a tree is a collection of trunk and branches and twigs and leaves which are, in their turn, collections of the atoms that compose them. We might look out over Paris from Montmartre and say ‘I’m looking at Paris’. Actually we are looking at a collection of rooves. The wholeness of things is an illusion.
Locke, however, soon ran into a problem. Seventeenth century science, which had provided him with the knowledge that whole things are actually assemblies of atoms, also told him that our sensations of warmth and cold and sweetness and colour are not in the things that we sense but in ourselves. What then of the idea that we only derive knowledge from sense impressions? If I stand away from the fire it is pleasantly warm, but if I stand closer to the same fire it feels unpleasantly hot. Sensations are not actuals but feelings. Locke’s answer to this conundrum is to make a distinction between what he called primary and secondary impressions. Primary impressions are those sensations we have of length and height and volume and speed, all the things physics studies in fact, these are indeed out there in the things we know. But our sensations of the qualities of things, their sweetness and colour and warmth and so on, are secondary impressions that arise from and remain within ourselves.
Until very recently indeed, Locke’s understanding of what things are and how we know them seemed to be fully vindicated by brain science. The foundation of modern neurological science was the realization that the brain is highly modular. The first discovery that a particular behaviour has its seat in a particular part of the brain was made by Paul Broca in 1861. There is a speech centre on the left hand side of the brain. It was not long before Wernicke found that understanding speech, which you might have thought was linked to doing it and therefore located in the same part of the brain, was in fact quite elsewhere, in the posterior part of the temporal lobe. During the First World War scientists were able to analyze the damaged brains of wounded soldiers and found other modules, most notably the visual. Gordon Holmes discovered that injury to only a tiny part of the visual field could induce blindness. In the nineteen thirties Werner Penfold located sensation and movement in two discrete bands of the sensory and motor cortex, running down both sides of the brain.
By the nineteen fifties the brain had been fully mapped. It was, in fact, both highly modulated and highly computerized, processing data in different departments so that it could appear in a comprehensible form in consciousness, as processed data appears on the monitoring screen of a computer. Just as Locke said, we do not sense whole things but different aspects of them through different senses, which, in the case of vision for example, are then relayed through the eye to different modules in the central cortex, before being associated in the outer cortex. The outer cortex was, indeed, often called the association cortex. Photons of light bounce off objects and information about their volumes and speeds and dimensions enters the eye through the retina, and, it was thought, is then processed to form a faithful point to point image of the object in the back of the brain. But just as Locke had said, or so it seemed, our sensations of their sensed qualities come from within our brains themselves. What is out there are light waves. Only light waves are out there and only they are known to physics. But our experiences of colour are, in Dawkins’ phrase, ‘arbitrary tags’ that the brain assigns to its analysis of the different wavelengths of light. Colour experiences result from the brain’s processing of the light waves and both begin and remain within the brain. There is no colour out in the world.
The first inklings that the brain’s processes might be far more complex than this came with the advent of positron emission topography (PET) scanning. Now, it was discovered, the brain does not form a faithful point to point image of what is out there at all. The senses do not make an impression on the brain as a signet ring leaves an impression in wax. It does not take pictures of the world but forms its own virtual replica of it. Sense data are merely agitations of nervous tissue by external stimuli. They are nothing more. The brain turns these electrical pulses into codes, encoding everything by which it is stimulated, thus transforming information about Locke’s primary qualities just as much as it does his secondary ones. The codes are as arbitrarily unrelated to the impulses they encode as the arbitrary noise’ firewood’, let us say, is to the stored carbon you burn. This explains, of course, or at least begins to, how it is that science tells us that things are made of atoms that are composed almost entirely of empty space, yet we see them as solids in which the parts are continuously contiguous. Even solidity is not out there, but manufactured by the brain. In what for me is an otherwise worthless book, The God Delusion, Dawkins has written an absolutely brilliant final chapter called Seeing Through a Burkah, in which he explains how we see physical reality only through a tiny aperture of sensation. If our senses were different we would see it quite differently. We would see a straight line, a goalpost say, not as a length of wood but as a continuously shifting engagement of the different atoms that compose the air interchanging with atoms of carbon in the wood.
The other astounding discovery that PET revealed was that the brain is far more modular than had even been thought. Vision, for instance, is not processed in one module of the brain. Instead information passes from the retina through immensely complex channels in the lateral geniculate nucleus to a reception area called V1, where in a series of blob like cells it is differentiated and encoded before being passed on to V2. In V2 the information is re-coded again in quite different cells that are not blob like but occur in strips. From V2 different streams of information are passed to different processing areas that are in quite different parts of the brain, not even in the central cortex as had always been assumed, but in the association cortex. V3 deals with depth and distance, V4 with colour, V5 with movement and V6 with relative position. But if data is so extremely fragmented and dealt with in such different areas of the cortex, how is it that we have an integral experience of objects in the world? Our experience of objects as whole things – we do not see a spasm of movement and, quite separately, a blur of colour and then a skeleton of lines and volumes somehow isolated from distance, and only then relative position, but a red bus on the other side of the road – this integrity of vision does not sit easily with the idea of a modular brain. The explanation of association in the outer cortex had, in fact, always been generalized and vague. It now became apparent that there was no associating going on in the outer cortex. There was no area of the brain to which all these different modules report. There is, as William James put it over a century ago , no ‘pontifical neuron’. How then does the brain integrate experience?
To complicate the picture even further, in The Vision of the Brain Professor Zeki produces evidence to show that the brain processes vision, for example, sequentially through V1 and then in V2 before dispatching information to the appropriate areas of V3 to V6, and cannot produce its visual sensations until this sequential process has occurred, yet at the same time V3 to V6 are already influencing and altering the information that is being passed to them from V1. There is, he thinks, a feedback process that ‘constitutes a powerful means by which one area can influence the area it receives an input from, perhaps even modifying the responses that it will receive before it receives them’. [1] The brain is holistic in its operations. It does not associate experience in any particular part of the brain but, as it were, nowhere and in no time. No longer can we think of things and how we know them as Locke did. We need a completely different paradigm of what things are and how we know them. The brain evolved in relation to the things it had to know. What then does what we now know about the processes of its knowing tell us about the things it knows?
