We’re no slaves to our senses

Twenty years ago, a new technique for directly investigating brain activity, called positron emission tomography (PET), became available.

PET involves the injection of a radioactive isotope that rapidly decays in the bloodstream of the volunteer (1). As the isotope decays it causes the emission of energy, which can be detected outside the body, and as the brain requires blood for energy, areas that are more active receive more blood and thus more energy is detected from those areas. Therefore, using this technique, a picture of what the brain is doing when somebody thinks, acts or feels can be built.

By chance I was able to take part in a PET project as part of my undergraduate research and then pursue that work for my PhD (2). There was a considerable buzz about the possibilities afforded by direct access to brain function and it was widely expected that the major psychiatric disorders– schizophrenia, chronic depression, obsessive disorders, autism and many more – would soon be resolved using these techniques. Although PET and, more recently, fMRI have provided many new insights and theories, breakthroughs in treatment for the major psychiatric disorders remain notably absent (3).

There are two major reasons for the lack of new treatment. The first is that although technologies to directly represent brain function are exciting and visually compelling, they still only provide a limited amount of detail. Imagine trying to figure out what is happening inside the Empire State Building by watching the lights go on and off. You might get some idea as to the internal function, but not much. Now imagine that you can change the pattern of lights by setting off sirens outside, directing heat at the building or sending somebody inside with a chocolate cake. You might, through careful observation, be able to work out those areas of the building that have good sound-proofing or air conditioning and where the kitchens are located. But your knowledge of what is happening inside will always be limited by your method of investigation.

The same problem faces those of us who hope to understand brain function. The things that we can measure (blood flow in the brain, the electrical and magnetic output of the brain, neurochemical concentrations in the brain, and so forth) are just too simple. We need more knowledge and more detail before we can possibly understand what is happening inside. These limitations explain at least some of the frustrations in trying to advance psychiatry and likely explain the lack of advance in understanding at least some specific disorders.

But there is a further reason why our understanding is lagging behind expectation. The facts provided by brain imaging, and other associated brain-based investigations, are the wrong sorts of facts. Neuroscience provides the wrong sort of knowledge to answer at least some of the questions we are asking about psychiatric illness.

Professor Chris Frith, as he describes in his new book Making up the Mind: How the Brain Creates our Mental World, has dedicated much of his academic career to the study of schizophrenia. Schizophrenia is a highly complex psychiatric disorder where the person suffers from, amongst other things, distorted thinking, hallucinations, and a reduced ability to feel normal emotions.

As Frith explains: ‘There are no objective physical signs of schizophrenia. The diagnosis is based on what the patient tells the doctor. Patients say that they hear voices when no one is there (false perceptions – hallucinations). Patients describe how they are persecuted by their colleagues at work when there is no evidence that this is the case (false beliefs – delusions). Patients with hallucinations and delusions are sometimes described as being out of touch with reality. But it is the mental world, rather than the physical world, that they have lost touch with.’

Not unreasonably, Frith describes schizophrenia as the consequence of some damage to brain function, damage that we don’t yet fully understand. He makes the very plausible case that if we can understand how mental function comes about in people without schizophrenia we will be better placed to understand how mental function goes so terribly wrong in people with schizophrenia. This draws Frith, and the reader, on to difficult terrain where questions such as ‘what is perception?’, ‘how do we form beliefs?’ and ‘how do we will?’ must be answered.

Frith’s general thesis is that all these questions can be answered by understanding how the brain works, and he begins by pointing out that normal brains do all kinds of things without us being aware of it. Toss a ball up into the air and catch it, for example, and your brain will perform multiple differential equations that you will never be aware of. The calculations and assumptions that our brains make can cause us to make mistakes such as in the Muller-Lyer illusion illustrated below.

In this illusion the lines appear to be different lengths, but, in fact, the lines are all identical in length (get out a ruler if you don’t believe me). Even when you know that the lines are the same length your brain will continue to tell you that they are different. This is an everyday hallucination created by the hidden assumptions your brain makes about how the world is organised. The illusion occurs because the visual-system processes that judge depth and distance assume that the ‘angles in’ configuration corresponds to an object that is closer, and the ‘angles out’ configuration corresponds to an object that is far away. Because the lines are actually the same size, the one that is perceived as being farther away is experienced as being larger than the one perceived as being closer.

An obvious question is, ‘why do our brains do that?’ Frith explains that our brains make assumptions because sensation is simply too ambiguous and if we were always processing sensation we would have no time for anything more interesting: ‘Couldn’t the system be tuned so that the sensory signals always dominated our experience? Then hallucinations could not occur. In fact, this is a bad idea, for many reasons. Sensory signals are simply too unreliable. But more importantly, such domination would make us slaves to our senses.’

Descartes explained long ago that while the mind is clearly exposed to sensory information, it is not drowned or dissolved by the senses (4). Human beings are self-located within sensory experience, but we are not sensorily immersed; our intuition of ourselves as particular things with particular location and experience is opened up by, rather than collapsed into, our senses.

At first glance, the fact that our brain filters and constrains what we can see is a challenge to the notions of reality and free will. After all, if our brain has already decided what we are going to perceive, then in what sense can we perceive the world as it truly is? And if our brain is making decisions for us, in what sense can we act on the world according to our own free will? Consequently Frith argues that what we see is not the world as it truly is, but an illusion: ‘Even if all our senses are intact and our brain is functioning normally, we do not have direct access to the physical world. It may feel as if we have direct access, but this is an illusion created by our brain.’

And he expresses considerable ambivalence regarding the nature of our conscious minds and the possibility of free will. ‘I am a materialist’, he writes. ‘But I admit that sometimes I sound like a dualist…. On the other hand I am firmly convinced that I am a product of my brain, as is the awareness that accompanies me.’ He also says, ‘My beliefs on free will are very ambivalent. What I do know is that I have a very strong experience of free will’.

Frith’s dual contentions that reality is illusory and free will is just a manufactured state of mind are both far too strong. Our limited direct access to the world ‘as it truly is’ is certainly a real problem. It is a problem because the world does not divide itself into fact-sized chunks that can be consumed by our senses. Whether a forest is perceived as a unit or an aggregation of many trees is arbitrary, just as it is arbitrary whether we observe leaves as independent or continuous with twigs and whether the twigs are independent or continuous and so on ad infinitum. Nature does not inherently divide itself into salient pieces, and what is salient or important is only revealed in the relationships within nature. Cows, for example, endow grass with the character of food because of the relationship between cows and grass – namely the consumption of the latter by the former. And it is in the character of cows to recognise grass as a source of nourishment.

Similarly, it is only through our relationship with the world that we can come to divide the world and begin to describe it. The facts that we can lay claim to about the world are arbitrary in so far as they are selected from an almost infinite number of potential facts, but we can, nevertheless, have great confidence that the facts we are gathering are real. We can have this confidence because our actions based upon those facts generally lead to expected outcomes – trains move forward through space, telephones transmit recognisable voice signals, medical intervention saves lives, and so on. These happy outcomes indicate that our division of the world is grounded in reality and that although our facts are arbitrarily selected we are not making them up as we go along.

In short, Frith misses, or understates, the role of inquiry in constructing a real representation of the world. Inquiry brings human beings into an understanding of the world that continues to more closely approximate the way the world truly is. The constraints that our brain places upon inquiry do not dictate reality but rather allow us the freedom to interrogate reality. Just imagine, as Descartes did, that we can be liberated from the constraint of the body and exist only as pure thought. What greater freedom could one possibly enjoy? No longer bound by space or time, such a being would be free to traverse the universe at will. Except that such an undifferentiated and locationless being, no longer tensed in time, would be unable to separate past, present and future or to separate here from there. With no fixed abode in time or space there would be no means by which experience could be determinate and no features to discriminate the specific from the general. It is precisely the constraint of a body, existing in the here and now, which enables a specific viewpoint to flourish and an independent existence to announce itself (5).

Constraint upon our embodied action is also necessary for free will. If every action were driven by conscious agency then we would be overwhelmed by the effort of trying to control all the relevant parameters with the requisite precision just as our senses would be drowned by information if there were no filtering. Constraint is necessary to allow coherent goal-directed behaviour and coherent percepts (6, 7). At the same time, however, we cannot be downloading a fixed set of responses or experiencing a fixed set of percepts because our behaviour would not contain the flexibility that we have evidently wielded to construct trains, telecommunication, modern medicine and so forth. In sum, our behaviour is both constrained and indeterminate, where constrained most certainly does not mean controlled and indeterminate most certainly does not mean random.

The negotiation of constraint and indeterminacy is not substantive; it cannot be located in parts of the brain, boiled down and recorded on a graph. That negotiation is an active, lived process and free will is possible because of the uniquely human ability to interrogate nature. Early human mentality would have resided in the ability to put oneself into a relationship with the environment so as to call out specific stimuli such as food or warmth. Importantly, this is no longer a relationship that is dictated by anatomy or evolutionary instinct, but rather is one that is, minimally at first, breaking free from the pre-ordained possibilities provided by evolutionary history. This new relationship to the character of things calls upon a sentience that is inside the organism, but the entire process is not a purely mental product that can be located in the brain. This early mentality is that relationship of the organism to stimuli in the environment that are set free by exploration to address specific biological needs. Within that relationship, constrained by circumstance, constrained by the biological imperatives of survival and reproduction, and constrained by historical development, freedom and agency begin. This is quite different from the engagement with stimuli driven by programmed behaviours and fully constrained by anatomical limitations. For early humans, there is a transformation from stimulus-response behaviour to inquiry.

The fundamental mistake that Frith makes – and this is a common error – is to believe that agency or free will are products only of the human brain. The brain is necessary but it is not sufficient, and chasing agency into the brain will only yield disappointment or, in this case, a sense that agency is illusory. If agency is not merely a product of ordinary brains, then it follows that abnormal brains might not be the whole or only answer when there are psychiatric problems and delusions of agency such as in schizophrenia.

To his tremendous credit, Frith is ready to push neuroscience past the hype that can be generated by a pretty picture and into a deeper understanding of what makes mental function. For that alone, Making up the Mind should be read by anyone interested in understanding contemporary neuroscience. The idea, however, that the brain constructs the mind is incomplete, and the quicker we realise that, the quicker we will make progress in understanding both normal and abnormal minds.

Stuart Derbyshire is a senior lecturer in psychology at the University of Birmingham, England, and director of pain research at the Birmingham University Imaging Centre.

Making up the Mind: How the Brain Creates our Mental World by Professor Chris Frith is published by Blackwell Publishing. (Buy this book from Amazon(UK).)

(1) PET scanning utilizes biological molecules synthesized with radiolabeled isotopes, such as 15O-labeled water, created in a cyclotron. The 15O-labeled water stabilises by emitting a positively charged electron (or positron, hence positron emission tomography). Once the positron is emitted it will soon meet an electron and the electron and positron will be annihilated in the collision producing a burst of energy that pass straight through the volunteer and can then be detected. By injecting 15O-labeled water and placing detectors around the volunteer’s head a picture of where the emissions are occurring can be created and that picture will index where activity in the brain is taking place.

(2) Cerebral responses to pain in patients with atypical facial pain measured by positron emission tomography’, Derbyshire SWG, Jones AKP, Devani P, Friston KJ, Feinmann C, Harris M, Pearce S, Watson JD, Frackowiak RSJ, Journal of Neurology Neurosurgery and Psychiatry 57: 1166-1172, 1994

(3) The physical basis of fMRI is the difference in the magnetic properties of oxygenated and deoxygenated blood, specifically the difference in decay time of the MR signal from oxyhemoglobin and deoxyhemoglobin. This difference in signal characteristics allow for the localized detection of blood flow in the brain similar to that from PET imaging but with potentially greater temporal and spatial sensitivity.

(4) Meditations on First Philosophy, Rene Descartes (1641). Translated by ES Haldane and GRT Ross in Descartes Key Philosophical Writings, Wordsworth Classics, 1997, pp. 139-146.

(5) The Knowing Animal: A Philosophical Inquiry into Knowledge and Truth, Raymond Tallis, Edinburgh University Press (Edinburgh), 2005

(6) ‘Visual detection is gated by attending for action: Evidence from hemispatial neglect’, Rafal, R. D., Danziger, S., Grossi, G., Machado, L. & Ward, R. Proceedings of the National Academy of Sciences U.S.A. 99, 16371-16375, 2002

(7) The Hand: A Philosophical Inquiry into Human Being, Raymond Tallis, Edinburgh University Press (Edinburgh), 2003