by Ian Gold


Interactions between Philosophy and Neuroscience

Philosophy interacts with neuroscience in two different ways, although the boundary between the two is fluid. The first kind of investigation, usually referred to as philosophy of neuroscience, is concerned with philosophical questions raised by neuroscientific data or theory, or by the status of neuroscience as a whole. The second kind of investigation, usually called neurophilosophy, attempts to exploit advances in neuroscience to solve philosophical problems about the mind. The philosophy of neuroscience is thus a branch of the philosophy of science. Neurophilosophy, in contrast, is a branch of the philosophy of mind and is closely related to cognitive science.

Because both of these branches of philosophy are of recent vintage, general principles and clear foci have not yet been identified; nor are there many clearly delineated ‘debates’ that characterize more established areas of philosophy. For these reasons, no attempt is made here to present a comprehensive picture of the field. Instead, this article discusses some representative illustrations of work in neurophilosophy and philosophy of neuroscience. Many philosophers of neuroscience – like some neuroscientists themselves – are also pursuing research that is better described as theoretical neuroscience. This is not dealt with here.


The modern incarnation of the view that the mind is identical to the brain and its functions was introduced into psychology and philosophy in the late 1950s. This doctrine, known as the identity theory, was eventually supplanted by functionalism, according to which mental states are to be analyzed in terms of their relations to one another, to perceptual input, and behavioral output. Functionalism holds that any material that embodies these relations – the silicon chip of a computer, for example – has a mind. Thus, while the view that the mind is to be explained by science has been the overwhelmingly dominant position in contemporary philosophy, the brain and its properties had been, until recently, as little emphasized in philosophy as in cognitive science and artificial intelligence research.

Against this mainstream position Patricia S. Churchland (1986) articulated a new vision for the philosophy of mind which she called neurophilosophy. With Paul M. Churchland, she has continued to argue that an understanding of the mind requires abandoning the purely functional investigation of philosophy and cognitive science in favor of a biologically based science of mind. Indeed, the Churchlands have defended the view that a successful theory of the mind will be exclusively neuroscientific (see below).

Although philosophical work deserving the name ‘neurophilosophy’ had existed prior to 1986, Churchland's book baptized new branches of the philosophy of mind and science, and this has produced a new generation of philosophers whose work straddles the boundary between philosophy and neuroscience. Even if functionalism, broadly speaking, remains the right framework for a theory of the mind, the specific details of biological minds is of independent interest. Further, the facts of how natural minds operate may provide novel ideas for the development of artificial intelligence systems.

Neurophilosophy: Philosophy of Mind and Epistemology

Neurophilosophers have addressed a wide variety of traditional problems in philosophy by applying the findings of neuroscience. In what follows, five representative illustrations are presented.

Perception and Intentionality

Perhaps the most significant and striking fact about mental states is that they are about things in the world. This ‘aboutness’ is usually referred to as the intentionality of mental states, and it is closely related to what is often called perceptual content – that is, how perception represents the world to be. How this is possible, and how it occurs, are two of the most important questions in the philosophy of mind. A paradigm case of the intentionality of the mental is the putative intentionality of perceptual states. When I stare at the ocean from my window, I am in a visual state which is about the ocean. Because this case seems simpler than many others – for example, my ability to imagine what it would be like to visit the Taj Mahal – theories of intentionality often begin with perception as a first step in the development of a comprehensive theory of intentionality.

Kathleen Akins (1996) argues that the relation between sensory states and what they represent may be quite different from the received view about intentionality. According to that view, sensory states represent aspects of the external world which are, typically, informative for the organism. Akins doubts that this is generally true; sometimes sensory states are not about the external world in the familiar sense. An investigation of sensory states, therefore, may not illuminate the ‘aboutness’ of mental states in the traditional sense.

Akins's argument takes as an illustration the simple sensory system of temperature detection or thermoreception. According to the received view, the purpose of thermoreception is to represent the temperature of the environment to the organism, and this view assumes that temperature receptors function like thermometers. However, the neurophysiology of thermoreception reveals a rather different picture. Temperature receptors do not function like thermometers; they are nonlinear and produce exaggerated responses to temperature changes. The reason for this, according to Akins, is that thermoreception is, as she says, ‘narcissistic’. It functions not to give the organism information about the temperature of the environment, but rather to tell the organism how the temperature of the environment affects the organism. Consider, for example, the familiar illusion that comes from running one hand under cold water, one under hot, and then putting both into the same tepid water. One hand will report that the water is hot, the other that the water is cold. On the view that perception is designed to reveal the way the world is, this is a spectacular failure. On the narcissistic view, however, it is a success because each hand is reporting something of relevance, namely, that its environment is rapidly heating or cooling. Because rapid changes in temperature are of great practical importance to organisms, this is important information.

A neurophysiologically inspired conception of sensory function, therefore, produces a rather different picture of perception from the traditional one. If this picture is correct, whatever the lessons of perceptual systems for the nature of intentionality, there is no simple and direct route from the properties of sensory systems to the nature of intentionality.


The nature of conscious experience and its relation to the external world is a perennial concern of the philosophy of mind and epistemology, and pain experience is a common test case for this investigation. There is, however, considerable controversy over what pain reveals about the mind, and the phenomenon of pain has been used as a way of defending myriad views; for example: that some mental states are entirely subjective; that we have a special access to the states of our own minds; that experience has properties that cannot be explained in purely physical or functional terms; that the mind is something over and above the brain; and that some aspects of our experience are entirely mysterious.

Pain experience is often used as a test case because it is thought to be a ‘simple’ kind of experience. As against this view, however, Valerie Gray Hardcastle (1997a) argues that philosophical confusions about pain arise as a result of a failure to understand the neural complexity of pain, in particular, the fact that pain perception is an overarching process made up of a number of subsystems. These include systems that subserve the conscious experience of pain, the sense of suffering typically associated with pain, the affective-motivational aspect of pain, and pain behavior.

Hardcastle argues that philosophers have tended to identify pain with only one of these subsystems and have therefore drawn erroneous conclusions about pain as a whole. She further argues that a correct understanding of pain requires positing two broad pain mechanisms, the first responsible for the experience of pain and the second responsible for the inhibition of pain experience. Each of these putative systems explains many of the features philosophers have thought ascribable to pain as a whole, and together they resolve many philosophical disputes about pain. Disagreement over whether pain is a ‘subjective’ or an ‘objective’ phenomenon, for example, results, on Hardcastle's view, from taking a part of the phenomenon for the whole. The existence of a pain sensory system explains many of the features of pain that have led philosophers to argue that pain is an objective phenomenon, whereas the existence of a pain-inhibiting system explains many of the features of pain that support a subjective account of it. Once pain is understood to be composed of both of these functionally distinct subsystems, the disputes over objectivity disappear.


The phenomenon of dreams has been a frequent case study in the history of philosophy's attempt to understand consciousness. The causes and function of dreams also, famously, take centre stage in psychoanalysis. Recent work in neurophysiology and neurochemistry has begun to elucidate the biological processes of sleep, including rapid eye movement (REM) sleep, the stage of sleep in which the sleeper dreams. The function of dreams, and what neuroscientific findings say about psychoanalytic theory, remain controversial.

What has recently occupied philosophers most about dreams is the question of whether they are genuine experiences. Dreamers awaken and believe that they have had experiences in dreams of events and adventures of various kinds. However, dream experience is very uncritical. For this reason, the mere memory of a dream is poor evidence for establishing that the dream experience has actually occurred. Other hypotheses – such as that dreams are confabulated upon awakening – are equally plausible and have been fodder for philosophers of mind of a skeptical bent who have denied that dreams are experiences.

Owen Flanagan (1996) argues that neurophysiology can do philosophical work here to refute this skeptical position. The relevant evidence comes from studies showing that the patterns of neural activity during REM sleep are highly similar to the patterns of activity in the waking state. This similarity provides evidence for the accuracy of dreamers' memories of their dreams: dreams are indeed experiences similar in some respects to waking experiences because the state of the brain in REM sleep is much like the state of the brain in wakefulness.

Flanagan (1995) also considers the question of what function dreams perform in mental life. He evaluates the recent neuroscientific theories of dreaming and argues that, strictly speaking, dreams perform no function in the cognitive economy of the dreamer. They are, rather, evolutionary ‘spandrels’ – phenomena that come into existence not because they themselves are adaptive but because they are necessary for, or are a by-product of, some other function that is selected for. Flanagan claims that dreams arise as a necessary, but nonfunctional, consequence of REM sleep though what the function of REM sleep itself is remains controversial. He suggests, however, that the practice of dream interpretation, ubiquitous both before and after Freud, can be thought of as a technique for self-reflection and understanding. Dreams can, in this sense, be seen to have a cultural, if not a psychological, function.


Dreams are sometimes said to be states in which dreamers are irrational. The concepts of rationality and irrationality have also been explored in neurophilosophy by the investigation of delusion. A paradigm case is the Capgras delusion in which sufferers become convinced that intimates (or sometimes significant objects) have been replaced by exactly identical duplicates. As if this is not strange enough, while sufferers are puzzled by this occurrence, they do not seem to be terribly troubled by it.

Other equally bizarre beliefs include the belief that one is dead (Cotard delusion); that one is being followed by familiar people in disguise (Fr├ęgoli delusion); that someone else is inserting thoughts into one's mind (delusion of thought insertion); that someone else is controlling one's actions (delusion of control); and that the person one sees in the mirror is someone other than oneself (mirrored-self misidentification). Traditionally, delusional subjects were referred to psychiatrists, and this practice continues. There is now evidence, however, that some delusions may be brought about by damage to the right hemisphere of the brain. Neuropsychiatrists have, therefore, begun to try to explain delusion in neuropsychological terms.

Two significant questions for neurophilosophy are: in what sense is delusion an instance of irrationality? And what is the correct account of the character of this irrationality? A number of possibilities have been suggested. One is that delusions are not irrational because they are attempts to explain very strange experiences. On this view, the delusional belief is a rational response to that experience. A second view holds that delusions are irrational to the extent that they represent biases in hypothesis-generation or in the evaluation of the plausibility of hypotheses adopted as beliefs. A third view holds that the irrationality of delusion lies in the way experience represents the world. According to this position, certain representations, though not full-blooded beliefs, none the less deserve to be called irrational.

A third question for neurophilosophy is: what, if anything, does the functional anatomy of delusion reveal about the functional organization of belief? Here research is just beginning. Martin Davies and Max Coltheart (2000; Davies et al., forthcoming) are defenders of the view that the source of delusion is to be found in a combination of a strange experience together with a second cognitive factor. They argue that while the strange experiences of delusional subjects could be explained in any number of reasonable ways – including that the subject has a mental or neurological disease! – delusional subjects opt for explanations that are impossibly far-fetched. Delusional subjects must, therefore, have some other cognitive dysfunction that does not prevent this extreme hypothesis from establishing itself as part of the subject's store of beliefs. If this view is correct, and if right hemispheric damage is confirmed as the site of damage in delusion, we would have the beginnings of a functional anatomy of belief.

Unity of Consciousness

An early illustration of the relevance of neuroscience to philosophy was provided by Thomas Nagel (1971), who discussed experiments with commissurotomy, or ‘split-brain’, patients in order to explore the traditional view that consciousness is unified – that our experience is constituted by a single stream of experiences of which we are aware. The neuropsychological phenomenon is well known. Individuals with severe epilepsy can be treated by severing the corpus callosum and anterior commissure (the bundle of fibres that connect the two hemispheres of the brain) in order to prevent the spread of epileptic fits. Despite the fact that subjects who undergo this surgery appear entirely normal in their everyday behaviour, studies of these individuals reveal subtle but dramatic behavioral effects. The absence of anatomical connections between the hemispheres prevents perceptual input from one hemisphere from being transferred to the other, and the behavior elicited from the patients makes it evident that the two hemispheres can function and drive behavior separately and, sometimes, competitively. However, because only one of the hemispheres (usually the left) subserves language, only that hemisphere can express the thoughts of the patient.

Nagel considers the question of what these phenomena say about the apparent unity of consciousness. How many minds exist within the body of the split-brain patient? Nagel considers five possibilities: (1) that there is one mind whose consciousness is located in the linguistic left hemisphere and whose right-hemisphere behavior is caused by a sort of automaton; (2) that there is one mind associated with the left hemisphere, but right-hemisphere behavior is caused by conscious mental activity that is unintegrated into the larger consciousness of the person; (3) that there are two minds only one of which can speak; (4) that there is only one mind, the contents of which come from both hemispheres and are therefore dissociated; and, finally, (5) that there is one mind when the two hemispheres are acting together but two minds when experimental conditions elicit different behavior from each separately.

Nagel argues that there are no principled reasons for choosing any of these options over the others and concludes, therefore, that there is no whole number of minds that can be associated with split-brain patients. The even more radical proposal that follows from this is that the same holds true of normal subjects. The belief that the mind is a single thing is an illusion, Nagel suggests, that arises because every agent experiences his or her own consciousness as unified and imports the assumption of unity into his or her experience of the minds of others. It is rather the case, Nagel argues, that a mind is a conglomeration of diverse functions that operate so harmoniously as to appear, from both the inside and the outside, as a single thing. The falsity of the appearance is revealed when the two hemispheres can no longer operate in concert.


Philosophy of Neuroscience and Its Relevance to Cognitive Science

Neuroscience and the Cognitive Sciences: Relations among Theories

In contrast to the interests of neurophilosophy, the philosophy of neuroscience investigates philosophical issues within the theories and practice of neuroscience itself. A number of issues have been addressed by philosophers of neuroscience including levels of explanation in cognitive neuroscience; the nature of representation; and the significance of neuroscientific evidence. Perhaps the central question that has been addressed thus far in the philosophy of neuroscience, however, is a very general one: what is the relation between the cognitive sciences and neuroscience? A number of relations are in principle possible, among them that neuroscience and cognitive science will provide separate but equal descriptions of the mind at different theoretical levels; that cognitive science will provide a functional description of the mind for which neurobiology will provide a mechanistic description; and that cognitive science will reduce to neuroscience as genetics reduces to molecular biology. In the process, it is likely that some parts of cognitive theory will be discarded and replaced by neuroscience.

The views of the Churchlands (see especially P. M. Churchland, 1981; P. S. Churchland, 1986; Churchland and Churchland, 1996) have focused debate in this area. They defend a view known as eliminative materialism. According to this view, the cognitive sciences will eventually be entirely replaced by a mature neural theory of the mind. The view is eliminativist because it holds that ordinary psychological concepts, and perhaps the concepts of theoretical cognitive science, will be eliminated and replaced by novel concepts from neuroscience.

Although according to eliminativism neuroscience will provide the final theory of the mind, the historical process of reaching this state of knowledge will, according to the Churchlands, involve a co-evolution of neuroscience and cognitive science. Results from neuroscience will, on this view, constrain cognitive models of mental phenomena which will, in turn, stimulate and direct investigation in neuroscience. Once neuroscience is sufficiently rich in theoretical resources, however, it will be in a position to explain mental phenomena directly. If this view is correct, then the consequences of eliminativism for cognitive science are dramatic. While cognitive science will play an important historical role in the development of the theory of the mind, it is neuroscience alone that will remain once the process of co-evolution is complete.

Eliminative materialism can be supported by a number of lines of argument, but two are particularly important. The first is based on the apparent fact that ‘folk psychology’ – the quotidian explanations of behavior by appeal to belief and desire – and, to some extent, cognitive science, have, according to the Churchlands, largely failed to provide adequate explanations of mental phenomena. One reason for this failure is that the fundamental psychological concepts are so flawed that no science based on them can get very far. Eliminativism concludes that they must be abandoned in favor of a set of concepts that is more promising.

A second line of argument proposes that psychological notions cannot be unified with the scientific world-view being developed by the other natural sciences. Only a biological science, such as neuroscience, is likely to produce a theory of the mind that will fit naturally into this picture. This argument has two possible conclusions: first, that neuroscience ought to be pursued and, second, that the unifiability of neuroscience with the natural sciences provides prima facie evidence that a neural theory of the mind will in fact be successful. The latter conclusion expresses the eliminativist view.

Beyond Eliminativism

Although eliminativism has been repeatedly challenged by philosophers of mind, it continues to represent a mainstream view among neuroscientists themselves. A different view is developed by Ian Gold and Daniel Stoljar (1999). They argue that the view that neuroscience alone will provide the successful theory of the mind embodies two quite distinct pictures of the development of the science of the mind that often fail to be distinguished. According to one view, ‘neuroscience’ can refer narrowly to cellular and molecular biology of the brain, or it can refer, more broadly, to the interdisciplinary effort to understand the mind and brain usually known as ‘cognitive neuroscience’. The eliminativist view that the biological science of the brain alone will provide the successful theory of the mind is a radical view, but it is not as yet supported by anything in neuroscience itself. All of the putative accounts of mental phenomena available in neuroscience – even those that are framed largely in neural terms – turn out to be amalgams of neurobiology and cognitive science. The present state of the sciences of the mind supports the view that the science of the mind is likely to be an interdisciplinary one.

In contrast, the view that it is cognitive neuroscience alone that will provide the successful theory of the mind is not a radical thesis at all. It is simply the view that some combination of sciences will collectively explain the mind. In particular, this view does not entail, and the radical view does, that cognitive science will form no part of a final theory of the mind. These two quite distinct views are regularly conflated and lead to a distorted picture of the current state of neuroscience. Which sciences will provide the necessary theoretical concepts, and what their relative contributions to successful theory will be, remain open questions.

Interpreting Neuroscience: An Illustration

In addition to addressing the status of neuroscience as a whole, the philosophy of neuroscience is concerned to elucidate particular neuroscientific concepts and their role in theory. One example of the kind of question that is of interest to the philosophy of neuroscience comes from the theory of vision and its relation to the investigation of consciousness. It will be clear that this problem is closely connected to the neurophilosophical discussion of consciousness described above and exemplifies the fluidity of the boundary between neurophilosophy and the philosophy of neuroscience.

Visual experience represents the environment as having a range of different properties such as color, shape, and motion, and the perception of these features are subserved by different cortical regions. These elementary facts raise a family of questions that is usually referred to collectively as the binding problem: how do brain areas interact so that the color of a stimulus, for example, is associated with its shape? And how does this neural activity produce perceptual experience that is unified?

One recent proposal about how the binding problem is solved at the level of neurons runs as follows. Many neurons exhibit regular physiological patterns of firing called oscillations, and it has been suggested that synchrony of oscillation (especially around the frequency of 40 cycles per second, or 40 Hertz) is a sign of functional connection. If two neurons, one responsive to color and one to edges, were to fire synchronously, this temporal property could signal that the two neurons were responding to the same stimulus. Stimulus identity and perceptual coherence would thus be captured by the temporal features of neural activity. It has further been suggested that synchronous oscillatory firing could be a marker of perceptual consciousness. According to this view, 40-Hz oscillation not only solves the binding problem but brings the stimulus so bound into consciousness.

There has been a good deal of debate about the 40-Hz proposal, and it raises many questions, some empirical, some theoretical. Does 40-Hz oscillation have the right properties to solve the binding problem? What is the relation between neural oscillations and the computational processes posited in cognitive theories of vision? What exactly is the relation between binding and consciousness? Does the 40-Hz theory address both problems equally well? Will the 40-Hz account generalize to other perceptual modalities? If not, how is the binding problem solved across modalities? Some of these questions are being addressed by philosophers together with cognitive and neuroscientists, and it is this kind of investigation that may represent the collaborative and interdisciplinary future of the theory of the mind.


An operation in which the bundle of fibers connecting the two hemispheres of the brain, the corpus callosum, is cut.
Eliminative materialism
The philosophical view that the posits of (at least) folk psychology will be discarded in favor of a neuroscientific theory of the mind.
Folk psychology
The ways in which ordinary people understand and explain their own and other people's behavior.
In the philosophy of mind, the doctrine that mental states are distinguished from one another by what they are typically caused by and what they typically cause.
Identity theory
The theory that mental events are identical with brain events.
The property possessed by mental states such as beliefs and thoughts of being ‘about’ things, or having content or meaning.
The application of advances in neuroscience to problems in the philosophy of mind.
Philosophy of neuroscience
The study of philosophical questions prompted by concepts and theories within neuroscience.
Rapid eye movement (REM) sleep
The stage of sleep in which dreams occur.
The sensory detection of temperature

  • Akins K (1996) Of sensory systems and the aboutness of mental states. Journal of Philosophy 93: 337–372.
  • Churchland PM (1981) Eliminative materialism and propositional attitudes. Journal of Philosophy 78: 67–90.
  • Churchland PS (1986) Neurophilosophy. Cambridge, MA: MIT Press.
  • Churchland PM and Churchland PS (1996) Replies from the Churchlands. In: McCauley RN (ed.) The Churchlands and Their Critics. Oxford, UK: Blackwell.
  • Davies M and Coltheart M (2000) Introduction: Pathologies of belief. Mind and Language 15: 1–46.
  • Davies M, Coltheart M, Langdon R and Breen N (forthcoming) Monothematic delusions: towards a two-factor account. Philosophy, Psychiatry, Psychology.
  • Flanagan OJ (1995) Deconstructing dreams: the spandrels of sleep. Journal of Philosophy 92: 5–27.
  • Flanagan OJ (1996) Prospects for a unified theory of consciousness. In: Cohen J and Schooler J (eds) Scientific Approaches to the Study of Consciousness: 25th Carnegie Symposium. Hillsdale, NJ: Lawrence Erlbaum Associates.
  • Gold IJ and Stoljar D (1999) A neuron doctrine in the philosophy of neuroscience. Behavioral and Brain Sciences 22(5): 809–830.
  • Hardcastle VG (1997a) When a pain is not. Journal of Philosophy 94: 381–406.
  • Hardcastle VG (1997b) Consciousness and the neurobiology of perceptual binding. Seminars in Neurology 17: 163–170.
  • Nagel T (1971) Brain bisection and the unity of consciousness. Synthese 22: 396–413. 
Further Reading

  • Bechtel W, Mandik P, Mundale J and Stufflebeam RS (eds) (2001) Philosophy and the Neurosciences: A Reader. Oxford, UK: Blackwell.
  • Bickle J (1998) Psychoneural Reduction: The New Wave. Cambridge, MA: MIT Press.
  • Coltheart M and Davies M (eds) (2000) Pathologies of Belief. Oxford, UK: Blackwell.
  • Crick F and Mitchison G (1995) REM sleep and neural nets. Behavioural Brain Research 69: 147–155.
  • Dennett DC (1976) Are dreams experiences? Philosophical Review 85: 151–171.
  • Flanagan OJ (2000) Dreaming Souls: Sleep, Dreams, and the Evolution of the Conscious Mind. New York: Oxford University Press.
  • Fodor J and Pylyshyn Z (1988) Connectionism and cognitive architecture: a critical analysis. Cognition 28: 3–71.
  • Hardcastle VG (1999) The Myth of Pain. Cambridge, MA: MIT Press.
  • Hobson A (1999) Dreaming as Delirium. Cambridge, MA: MIT Press.
  • Munro A (1999) Delusional Disorder. Cambridge, UK: Cambridge Univerisity Press.

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