In 1996, the Australian philosopher David Chalmers gave a handy name to a phenomenon which had been known for centuries: the problem of how brain states can engender mind states. He dubbed it “the hard problem”. It describes a mystery with which we are all unwittingly aware.
When we win a prize most of us react with glee. When we come to harm, most of us react with sadness. A prize, like money or a trophy, is a physical thing, just as falling ill or being injured in an accident are physical in nature. Yet these physical happenings produce what looks like immaterial psychological states. It also works in the opposite direction. Most of us are happy about the idea of spending a sunny afternoon on the beach. And this expectation, this mental state, makes us get into the car, equipped with sun cream, towels and picnic, and drive to the beach. A mental event produces a physical event. How is it possible that a physical, bodily event can produce a mental, psychological event and vice versa?
Perhaps we could just ask a qualified brain surgeon to open a person’s skull and look inside. The surgeon will see the physical brain and its biochemical processes. Imagine we have a multilingual subject and ask them to read a passage from books written, say, in English, French and Spanish. The subject’s skull is exposed, and the surgeon can indeed see activity in the Broca area of the brain. The Broca area is a region in the frontal lobe of the dominant hemisphere of the brain whose functions are linked to speech production. The surgeon observes a correlation between activity in the Broca area and linguistic function. But our imaginary brain surgeon is more ambitious and aims at a causal explanation: can the scientist tell from the activity in the Broca area which language the person is currently speaking or, more to the point, what the sounds mean?
Neuroscientists, philosophers and psychologists all agree that the answer is “no”. There seems to be a correlation between a certain region of the brain and linguistic ability, but it does not amount to a causal connection. The processes in the Broca area do not answer the question why they make a speaker pronounce, say, meaningful French rather than Spanish sentences. There are correlations between brain states and mental states just as there exists a correlation between day and night. The day does not “cause” the night, and the night does not “cause” the day.
However, the analogy stops here. Underlying the correlation between day and night is the position of the Earth in the solar system and its daily rotation on its own axis. The latter is the cause of succession of day and night. But what particular brain state brings about a particular mental or psychological state? This question has proved to be intractable – that is why David Chalmers called it the “hard problem”. He’s given the problem a convenient label. But it was René Descartes in the seventeenth century who proposed an influential “solution”.
Descartes held that the body was one substance and the mind was another; the former was material, the latter immaterial, but they were linked via the pineal gland. This so-called solution became known as Cartesian dualism. Unfortunately, it only pushed the problem a little bit further down the line: the pineal gland is a small endocrine gland, and it has a seat in the physical brain. Descartes may have thought that it was the “principal seat of the soul”, but this invites the question, how can a physical organ be the seat of an immaterial soul? Descartes did not solve the “hard problem”.
There have of course been many “solutions” since Descartes’ valiant attempt, often made in conjunction with genuine progress in other areas of science. The rapid advances in physics, the establishment of the Darwinian paradigm, and the emergence of AI have all inspired proposals to solve the “hard problem”. So far without success. It is the last or at least one of the last mysteries still standing. What these proposed solutions share, with very few exceptions, is the admittance of consciousness into the physical realm. Very few people nowadays cling to the Cartesian belief that the mind is a separate immaterial entity. If they agree with Descartes, they agree that the mind is not identical with the brain. But this agreement leaves us with a need to explain how the mind “emerges” from the brain.
The Australian philosopher David Armstrong defended the identity view. As he put it,
“Suppose that the physico-chemical view of the working of the brain is correct …. It will be very natural to conclude that mental states are not simply determined by corresponding states of the brain, but that they are actually identical with the brain-states, brain-states that involve nothing but physical properties.”
Such statements are not made only by philosophers. Patrick Haggard, professor of cognitive neuroscience at University College London, writes, “The neuroscientific view focuses primarily on brain mechanisms: behaviour, decisions and individual consciousness are all consequences of these mechanisms.” He goes on, “Neuroscience treats the ‘I’ as being synonymous with an individual’s brain.”
Haggard is not alone among neuroscientists. The German magazine Gehirn und Geist published a manifesto in 2004, signed by eleven neuroscientists, in which they expressed the view that mental processes – like imagination, feelings and decision making – could in principle be described in physico-chemical terms. What is left open or still debatable is whether these cognitive processes are merely correlated with brain processes or whether the stronger view holds, namely that the brain “causes” mental processes. At least one of the signatories of the manifesto, Wolf Singer, director emeritus at the Max Planck Institute for Brain Research, Frankfurt, accepts the latter view. The American neuroscientist Gerald Edelman, author of many books on this question, also defends this stronger thesis. According to Edelman the brain “engenders” the mind: “Although conscious states (C) accompany states (C’), it is the neural correlate C’ that is causal of other neural events and certain bodily actions.”
What’s the right way to think about all this? I decided to ask someone working at the sharp end of brain science. Baroness Susan Greenfield, CBE, is a senior research fellow at Lincoln College, Oxford and the author of more than 200 peer-reviewed articles on neuro-chemicals and brain function. She is the author A Day in the Life of the Brain, her latest book on what philosophers call the “mind-body” problem.
In this book Greenfield tackles the problem from an interdisciplinary perspective – a view which embraces neuroscience, psychology and philosophy. At the centre of her approach stand two notions which are familiar to philosophers of mind: emergence and the embodied mind. Mental processes arise from brain processes, and the mind is embedded in a physical and social environment. To readers familiar with philosophical discussions in the area of philosophy of mind, such an inclusive approach stands in stark contrast to other views, which also try to steer their way around the Cartesian rock. They either declare that the mind is actually identical with the brain or claim that the brain “determines” or “engenders” the mind.
Edelman’s view is known as neural Darwinism, but according to Greenfield the invocation of Darwinism does not get to the core of the problem. The core of the problem is how the physical brain leads to subjective experiences. She clearly supports the embodied mind view, favouring correlations over as yet unfound
ed causal claims. She concludes her book by writing:
“Until we can formulate or articulate what kind of solution would satisfy us, then surely it will be almost impossible to deliver even at the most abstracted mathematical level any kind of answer that goes beyond correlation to causality.”
So correlations “yes” but causality “no” or not yet. As she writes in A Day in the Life of the Brain,
“If we can establish accurate neural correlates, and it’s important to recognise that there will indeed be more than one, of moments of consciousness, than we can better understand how the phenomenological corresponds to the physiological – even though the causal connection still eludes us.”
I ask her about this distinction between correlations and causality, which, she says, bedevils neuroscience. It is drilled into philosophy students at an early stage. She says that “science is very good at correlations.” We can find correlations, but she won’t say how long it will take neuroscience to establish a causal mechanism which would demonstrate the link between brain states and mind states.
So what can neuroscience say about these neural correlations? There are two perspectives regarding this question, she says. On the psychological side Greenfield is not primarily interested in accounting for higher mental functions, like reasoning and decision-making. She wants to explain the raw subjective states – the first-person perspective – with which we are all familiar: the taste of chocolate melting slowly in your mouth, the sunshine on your face, the swishing roar of surf (in other words “qualia”). Her aim is to explain the first-person perspective from an objective third-person perspective, at which point neuroscience enters the scene. She draws a distinction between the “mind” and “consciousness”: we can lose our minds in moments of high emotion without losing consciousness; but in sleep consciousness is switched off whilst the mind is busy producing dreams.
A tension exists, however, between these two perspectives, between what we feel subjectively and what neuroscience can explain objectively. Neuroscience must explain how the subjective mind works. So there must be in the brain a correlate to the subjective mind. For Greenfield and her team the correlate exists in neuronal assemblies, which she defines as “variable, highly transient (sub-second), macro-scale groups of brain cells (for example, about 10 million or more) that are not confined to, or defined by, anatomical brain regions or systems.”
The neuronal assemblies exist at a mesoscale, midway between the micro- and the macro-level. In this scheme the neuronal assemblies do all the work. But how do they do it? Recall that there is no claim that they causally explain how the qualia come about. Furthermore, this neuronal approach denies that there is a one-to-one mapping between particular brain states and mind states. The brain does not have a “centre” which directs operations. Rather, brain regions contribute to the whole. In the language of neuroscientists, the brain is “holistic”, i.e. several regions of the brain are involved in mental activities. The brain is also adaptive and responsive to changes in the environment. Colour, for instance, is employed to influence consumer behaviour: red to sell luxury goods. It has also been linked with various mental perceptions. Blue is associated with creativity and imagination; while red is associated with warmth and cosiness. Open office spaces also encourage interaction between people since they suggest a greater sense of freedom.
In which way, then, do these neuronal assemblies contribute to the whole? Although she does not explicitly define the term, Greenfield repeatedly employs the notion of emergence. This notion, very familiar to philosophers, has the job of explaining how the third-person perspective could account for the first-person experience.
Emergence is an interesting term, which has been used in philosophical discussions in a number of ways. Through an emergent process a new phenomenon arises out of a number of component factors, and the new phenomenon, once it has appeared, can no longer be reduced to its ingredients. It has become a separate phenomenon, which may obey its own laws. When you bake a cake, you mix the ingredients to prepare a dough; it goes into the oven and thanks to the exposure to heat it becomes a cake. The cake is no longer reducible to its ingredients. It is qualitatively different from its components. The cake emerges through this whole process. An analogy suggests itself: subjective psychological states emerge from underlying objective brain processes, i.e. the neuronal assemblies.
Unfortunately every analogy is hampered by a disanalogy. A teacher may tell a student that the flow of electricity is like a water flow but water consists of water molecules whilst a current is made up of electrons. Electrons and water molecules are very different entities and obey different laws. So the problem with the notion of emergence, applied to neuroscience, is this: the emergence of the cake can be explained all the way from the mixture of the ingredients to the final emergence of the cake; and the glow of a light bulb can be explained in physical terms from the flow of electrons in a copper wire.
But the emergence of conscious states from neuronal activities must cross the Rubicon between the physical and the mental. It must explain, as Greenfield says, how to convert the water of the objective brain events into the wine of subjective consciousness. The age-old Cartesian problem even plagues the notion of emergence: for how can the neuronal assemblies, which are physical in nature, bring about the immaterial mental qualia? Hence even emergence does not deliver a causal explanation – it seems it is correlations all the way down.
I asked her about the progress which neuroscience has made, in her opinion, over philosophy. I reminded her of the many “models” which philosophers have proposed to crack the “hard problem”. But she does not even accept the term “model” to characterise her neuro-scientific account. The use of the term “model” implies that the salient features of the model target – the system to be modelled – are known. You can model planetary motions once you know the order and the orbit of the planets around the sun from observations. But according to Greenfield, neuroscience does not even know the salient features necessary to model the emergence of subjective consciousness. In other words it does not know, at this stage, how to separate the essential from the accidental features.
So has there been any progress at all? Yes, she argues, for neuroscientists carry out experimental work, which has led to the discovery of many correlations between our psychological states and neuronal processes with which they co-occur. But she does not believe that neuroscience will replace, say philosophy, in our attempt to solve the “hard problem”. For her, it has to be an interdisciplinary approach. Once the “mechanics” of the brain are known, the big questions of who we are remain.