Highlights
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Under profound anaesthesia, the brain’s electrical activity is almost entirely quietened – something that never happens in normal life, awake or asleep
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Somehow, within each of our brains, the combined activity of billions of neurons, each one a tiny biological machine, is giving rise to a conscious experience. And not just any conscious experience, your conscious experience, right here, right now. How does this happen? Why do we experience life in the first person?
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one of the most compelling aspects of the mystery of consciousness is the nature of self. Is consciousness possible without self-consciousness, and if so would it still matter so much?
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This book is about the neuroscience of consciousness: the attempt to understand how the inner universe of subjective experience relates to, and can be explained in terms of, biological and physical processes unfolding in brains and bodies
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The story I will tell is a personal view, shaped over many years of research, contemplation, and conversation. The way I see it, consciousness won’t be ‘solved’ in the same way that the human genome was decoded, or the reality of climate change established. Nor will its mysteries suddenly yield to a single eureka-like insight
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For me, a science of consciousness should explain how the various properties of consciousness depend on, and relate to, the operations of the neuronal wetware inside our heads. The goal of consciousness science should not be – at least not primarily – to explain why consciousness happens to be part of the universe in the first place. Nor should it be to understand how the brain works in all its complexity, while sweeping the mystery of consciousness away under the carpet. What I hope to show you is that by accounting for properties of consciousness, in terms of mechanisms in brains and bodies, the deep metaphysical whys and hows of consciousness become, little by little, less mysterious.
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I use the word ‘wetware’ to underline that brains are not computers made of meat. They are chemical machines as much as they are electrical networks. Every brain that has ever existed has been part of a living body, embedded in and interacting with its environment – an environment which in many cases contains other embodied brains. Explaining the properties of consciousness in terms of biophysical mechanisms requires understanding brains – and conscious minds – as embodied and embedded systems
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I don’t agree. In my view, consciousness has more to do with being alive than with being intelligent. We are conscious selves precisely because we are beast machines. I will make the case that experiences of being you, or of being me, emerge from the way the brain predicts and controls the internal state of the body. The essence of selfhood is neither a rational mind nor an immaterial soul. It is a deeply embodied biological process, a process that underpins the simple feeling of being alive that is the basis for all our experiences of self, indeed for any conscious experience at all. Being you is literally about your body.
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By the end of the book, you’ll understand that our conscious experiences of the world and the self are forms of brain-based prediction – ‘controlled hallucinations’ – that arise with, through, and because of our living bodies.
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These shifts in how we see ourselves are to be welcomed. With each new advance in our understanding comes a new sense of wonder, and a new ability to see ourselves as less apart from, and more a part of, the rest of nature.
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Our conscious experiences are part of nature just as our bodies are, just as our world is. And when life ends, consciousness will end too. When I think about this, I
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What is consciousness? For a conscious creature, there is something that it is like to be that creature
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For an organism to be conscious, it has to have some kind of phenomenology for itself.
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Wherever there is experience, there is phenomenology; and wherever there is phenomenology, there is consciousness
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This may seem obvious, but it wasn’t always so. At various times in the past, being conscious has been confused with having language, being intelligent, or
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exhibiting behaviour of a particular kind. But consciousness does not depend on outward behaviour, as is clear during dreaming and for people suffering states of total bodily paralysis. To hold that language is needed for consciousness would be to say that babies, adults who have lost language abilities, and most if not all non-human animals lack consciousness. And complex abstract thinking is just one small part – though possibly a distinctively human part – of being conscious
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It is widely agreed that experience arises from a physical basis, but we have no good explanation of why and how it so arises. Why should physical processing give rise to a rich inner life at all? It seems objectively unreasonable that it should, and yet it does.
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Chalmers contrasts this hard problem of consciousness with the so-called easy problem – or easy problems – which have to do with explaining how physical systems, like brains, can give rise to any number of functional and behavioural properties.
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Even after all the easy problems have been ticked off, one by one, the hard problem will remain untouched. ‘[E]ven when we have explained the performance of all the functions in the vicinity of experience – perceptual discrimination, categorization, internal access, verbal report – there may still remain a further unanswered question: Why is the performance of these functions accompanied by experience?’
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physicalism. This is the idea that the universe is made of physical stuff, and that conscious states are either identical to, or somehow emerge from, particular arrangements of this physical stuff
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idealism. This is the idea – often associated with the eighteenth-century Bishop George Berkeley – that consciousness or mind is the ultimate source of reality, not physical stuff or matter. The problem isn’t how mind emerges from matter, but how matter emerges from mind
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dualists like Descartes believe that consciousness (mind) and physical matter are separate substances or modes of existence, raising the tricky problem of how they ever interact
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As we’ll see throughout this book, the way things seem is often a poor guide to how they actually are.
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Functionalism is the idea that consciousness does not depend on what a system is made of (its physical constitution), but only on what the system does, on the functions it performs, on how it transforms inputs into outputs. The intuition driving functionalism is that mind and consciousness are forms of information processing which can be implemented by brains, but for which biological brains are not strictly necessary.
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the suggestion that the brain ‘processes information’ conceals some strong assumptions
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the question of what information ‘is’ is almost as vexing as the question of what consciousness is, as we’ll see later on in this book. These worries are why I’m suspicious of functionalism
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A computer that plays Go, such as the world-beating AlphaGo Zero from the British artificial intelligence company DeepMind, is actually playing Go. But there are many situations where this is not the case. Think about weather forecasting. Computer simulations of weather systems, however detailed they may be, do not get wet or windy. Is consciousness more like Go or more like the weather? Don’t expect an answer – there isn’t one, at least not yet. It’s enough to appreciate that there’s a valid question here. This is why I’m agnostic about functionalism.
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The first is panpsychism. Panpsychism is the idea that consciousness is a fundamental property of the universe, alongside other fundamental properties such
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as mass/energy and charge; that it is present to some degree everywhere and in everything
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The main problems are that it doesn’t really explain anything and that it doesn’t lead to testable hypotheses. It’s an easy get-out to the apparent mystery posed by the hard problem, and taking it on ushers the science of consciousness down an empirical dead end
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These ‘isms’ provide different ways of thinking about the relationship between consciousness and the universe as a whole. When weighing their merits and demerits, it’s important to recognise that what matters most is not which framework
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is ‘right’ in the sense of being provably true, but which is most useful for advancing our understanding of consciousness. This is why I tend towards a functionally agnostic flavour of physicalism. To me, this is the most pragmatic and productive mindset to adopt when pursuing a science of consciousness. It is also, as far as I am concerned, the most intellectually honest
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Despite its appeal, physicalism is by no means universally accepted among consciousness researchers. One of the most common challenges to physicalism is the so-called ‘zombie’ thought experiment
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Here’s why the zombie idea is supposed to provide an argument against physicalist explanations of consciousness. If you can imagine a zombie, this means you can conceive of a world that is indistinguishable from our world, but in which no consciousness is happening. And if you can conceive of such a world, then consciousness cannot be a physical phenomenon
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And here’s why it doesn’t work. The zombie argument, like many thought experiments that take aim at physicalism, is a conceivability argument, and conceivability arguments are intrinsically weak. Like many such arguments, it has a plausibility that is inversely related to the amount of knowledge one has
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Can you imagine an A380 flying backwards? Of course you can. Just imagine a large plane in the air, moving backwards. Is such a scenario really conceivable? Well, the more you know about aerodynamics and aeronautical engineering, the less conceivable it becomes. In this case, even a minimal knowledge of these topics makes it clear that planes cannot fly backwards. It just cannot be done
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According to the real problem, the primary goals of consciousness science are to explain, predict, and control the phenomenological properties of conscious experience. This means explaining why a particular conscious experience is the way it is – why it has the phenomenological properties that it has – in terms of physical mechanisms and processes in the brain and body. These explanations should enable us to predict when specific subjective experiences will occur, and enable their control through intervening in the underlying mechanisms. In short, addressing the real problem requires explaining why a particular pattern of brain activity – or other physical process – maps to a particular kind of conscious experience, not merely establishing that it does
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We would like to know what it is about specific patterns of activity in the brain – such as the complex looping activity in the visual cortex¶ – that explains (and predicts, and controls) why an experience, such as the experience of redness, is the particular way it is, and not some other way. Why it is not like blueness, or toothache, or jealousy
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Explanation, prediction, and control. These are the criteria by which most other scientific projects are assessed, regardless of how mystifying their target phenomena might initially appear
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Physicists have made enormous strides in unravelling the secrets of the universe – in explaining, predicting, and controlling its properties – but are still flummoxed when it comes to figuring out what the universe is made of or why it exists. In just the same way, consciousness science can make great
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progress in shedding light on the properties and nature of conscious experiences without it being necessary to explain how or why they happen to be part of the universe in which we live.
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The gold-standard definition of a neural correlate of consciousness, or NCC, is ‘the minimal neuronal mechanisms jointly sufficient for any one specific conscious percept’. The NCC approach proposes that there is some specific pattern of neural activity that is responsible for any and every experience, such as the experience of ‘seeing red’. Whenever this activity is present, an experience of redness will happen, and whenever it isn’t, it won’t.
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The great merit of the NCC approach is that it offers a practical recipe for doing research.
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The phenomenon of ‘binocular rivalry’ offers a helpful example. In binocular rivalry, a different image is shown to each eye – perhaps a picture of a face to the left eye and a picture of a house to the right eye. In this situation, conscious perception doesn’t settle on a weird face-house chimera. It flips back and forth between the face and the house, dwelling for a few seconds on each. First you see a house, then a face, then a house again … and so on. What’s important here is that conscious perception changes even though the sensory input remains constant. By looking at what happens in the brain, it’s therefore possible to distinguish brain activity that tracks conscious perception from activity that tracks whatever the sensory input happens to be. The brain activity that goes along with the conscious perception identifies the NCC for that perception.
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The deeper problem is that correlations are not explanations
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But if we instead move beyond establishing correlations to discover explanations that connect properties of neural mechanisms to properties of subjective experience, as the real problem approach advocates, then this gap will
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narrow and might even disappear entirely
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The optimism is that today’s consciousness researchers may be in a situation similar to that facing biologists, studying the nature of life, just a few generations ago. What counts as mysterious now may not always count as mysterious. As we get on with explaining the various properties of consciousness in terms of their underlying mechanisms, perhaps the fundamental mystery of ‘how consciousness happens’ will fade away, just as the mystery of ‘what is life’ also faded away
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Applying the same strategy to consciousness, in this book I will focus on level, content, and self as the core properties of what being you is all about. By doing so, a fulfilling picture of all conscious experience will come to light.
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In making these distinctions, I am not proposing that these aspects of consciousness are completely independent. In fact, they are not, and figuring out how they relate presents another significant challenge for consciousness science
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Consciousness instead seems to depend on how different parts of the brain speak to each other. And not the brain as a whole: the activity patterns that matter seem to be those within the thalamocortical system – the combination of the cerebral cortex and the thalamus (a set of oval-shaped brain structures – ‘nuclei’ – sitting just below, and intricately connected with, the cortex)
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What they did was simple and elegant. To test how different parts of the cortex were talking to each other, they stimulated activity in one location and recorded how this pulse of activity spread to other cortical regions over space and time. They did this by combining two techniques: EEG and transcranial magnetic stimulation (TMS). A TMS rig is a precisely controlled electromagnet which allows a researcher to inject a short and sharp pulse of energy directly into the brain through the skull, while EEG in this case is used to record the brain’s response to this zapping. It’s like banging on the brain with an electrical hammer and listening to the echo.
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Even though we do not directly feel the TMS pulses, Massimini and Tononi found that their electrical echoes could be used to distinguish different levels of consciousness. In unconscious states, like dreamless sleep and general anaesthesia, these echoes are very simple. There is a strong initial response in the part of the brain that was zapped, but this response dies away quickly, like the ripples caused by throwing a stone into still water. But during conscious states, the response is very different: a typical echo ranges widely over the cortical surface, disappearing and reappearing in complex patterns. The complexity of these patterns, across space and time, implies that different parts of the brain – in particular the thalamocortical system – are communicating with each other in much more sophisticated ways during conscious states than during unconscious states.
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While the difference between the two conditions is often easy to see simply by eyeballing the data, what’s truly exciting about this work is that the complexity of the echo can be quantified. It is possible to put a number to it to specify the magnitude of complexity. The approach is called ‘zap and zip’: use TMS to zap the cortex, and use a computer algorithm to ‘zip’ the response, the electrical echo, into a single number.
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In a landmark study from 2013, Massimini’s team measured the PCI values of a large number of patients with brain injuries who had disorders of consciousness. They found that PCI magnitudes correlated extremely well with levels of impairment, as independently diagnosed by neurologists
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In my research group at the University of Sussex, we’ve been working on similar methods to assess conscious level. But instead of using TMS to inject pulses of energy into the cortex, we’ve been measuring the algorithmic complexity of ongoing, natural – what we call ‘spontaneous’ – brain activity
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we discovered that the complexity of spontaneous cortical activity – as measured by EEG – reliably drops in both early sleep and anaesthesia. We also found that complexity during rapid eye movement (REM) sleep is much the same as during normal conscious wakefulness, which makes sense because REM sleep is when dreaming is most likely – and dreams are conscious
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In Owen’s experiment, a twenty-three-year-old woman, behaviourally unresponsive following a traffic accident, was placed in an fMRI scanner and given a series of verbal instructions. Sometimes she was asked to imagine playing tennis, while at other times she was invited to imagine walking around the rooms of her house. On the face of it, this seems a peculiar thing to do, since patients like this are not responsive to anything – let alone to complex verbal instructions. However, studies with healthy people have shown that the brain regions engaged by imagining fluent movements (like playing tennis) are highly distinct from those activated by imagining navigating through spaces.* Remarkably, Owen’s patient showed exactly the same pattern of brain responses, indicating that she too was actively following the instructions by engaging in highly specific mental imagery. It is almost impossible to conceive that anyone could do this while unconscious, so Owen concluded that the behavioural diagnosis of vegetative state was wrong, and that the young woman was in fact conscious