Mind-body problem
From Scholarpedia
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Author: Dr. John G. Taylor, King's College London
The mind and body appear on first view to be very distinct entities, but yet they interact most strongly in some as yet unknown manner. The nature of these two entities and their interaction poses the mind-body problem. Here we consider various solutions to the mind-body problem, especially those of a more physicalist character.
A new look at the mind-body problem
The mind is composed of mental fragments - sensations, feelings, thoughts, imaginations, all flowing now in an ordered sequence, now in a chaotic fashion. There are also non-conscious components involved in early brain processing of stimuli (as in lower level processing in vision, such as in V1) or in emotions not yet in consciousness. On the other hand the body is constructed under the underlying laws of physics, and its components obey the well-enumerated laws of physiology. It is these characteristic differences between these two - between mind and body - that lead to the Mind-Body problem.
The Mind-Body problem has been in existence for several thousand years - going back to Plato, Aristotle, The Buddha and many other ancient Greek and Eastern thinkers. The problem is simple to state: the mind and the body seem to be entities of very different kinds (as just described), so how do they interact so as to produce in a person a mind able to have effects on their body (as when the person wills the body to perform some act), whilst also their body can affect their mind (as in the experience of pain)? Although the problem is simple it has as yet no satisfactory solution, in spite of the amount of time and thought devoted to it.
Much has been written on the variety of solutions to the Mind-Body problem. There are the dualist solutions (mind and body are distinct, although then the problem of how they interact becomes even more embarrassing, and is so far unresolved in any satisfactory manner); the idealist solution (there is only mind, and body/matter is merely a manifestation of mind, although how mind could have created the beautiful subtlety of the unification of the nuclear, electromagnetic and radioactive forces of nature, with a proposed extension (yet unproven) to fusion of those forces with the force of gravity through superstrings, seems impossible to comprehend); a third position is that there is only body, so this is a reductive physicalist approach (but then how the amazing mental world full of our experiences is thereby created from matter has to be faced). There are also nuanced versions of one or other of these three initial positions for solving the Mind-Body problem, some having great sophistication and subtlety in themselves.
There is also the question of what exactly is the mind? It is certainly composed of conscious components, but it would also seem to contain non-conscious ones as noted earlier, such as unconscious emotions and low-level processing as yet out of consciousness; automatic motor responses are also below the radar of consciousness. These unconscious or pre-conscious components are not problematic since they do not possess apparently non-material private components like those that conscious components appear to do. A stone is not considered as having such private experiences as do we; it's responses to action on it can be described in purely physical terms. Similarly the non-conscious processes in our minds can be accepted as arising solely from suitable brain processing, so more easily understood as components of the body (especially with the great advances in brain science tracking down and modelling in detail this pre-conscious neural activity). These non-conscious components of mind do not have (by definition) any conscious component, so there is no difficulty in expecting them to arise solely from brain activity: they can therefore be seen as on the body side of the mind-body duo. Thus the truly inexplicable part of the mind - that part to which the epithet Mind-Body problem most closely applies - appears to be that of consciousness. That position is appropriate to take here because it addresses what appears to be the most difficult part of the overall problem of mind-body interaction: how conscious experience can interpenetrate and fuse with bodily activity to affect each other in the way mentioned in the first paragraph. Detailed neural models of the other (non-conscious) components of brain activity are increasingly convincing such as for predictive value coded by dopamine, for motor responses guided by internal motor models, and for early models of visual and other sensory processing through a hierarchy of increasingly complex feature detectors; they clearly support the lack of any nonconscious mind-body gap. In support of the approach used here is that it is more in line with modern thinking on the Mind-Body problem, especially that brought to the fore by Descartes and since emphasised in the notions of the hard problem (Chalmers, 1996) and the explanatory gap (Levine, 1983); these specifically emphasise the gap between consciousness and brain activity.
The traditional mind-body problem
The traditional approaches to the Mind-Body problem were mentioned briefly above - the core concepts of dualism, idealism and physicalism, together with the numerous varieties in between involving mixtures and modifications. A set of references to these more traditional approaches are given at the end of this article (under General references to the mind-body problem). A brief expansion of this description is appropriate in any discussion of the Mind-Body problem.
Dualism supposes that there two ontologically distinct entities, mind and body. The distinction may arise from body and mind being composed of distinct substances (substance dualism) or from the same substance but with distinct functions (function dualism). The dualistic concept can be traced back to Zoroastrianism at around 1000BC, and is involved heavily in parts of Buddhist philosophy as well as in modern religious beliefs.
There are numerous varieties of dualism: interactionism (where mind and body interact in a manner as yet completely unknown to achieve the apparent effects of mind on body and vice versa which were mentioned earlier), epiphenomenalism (where the mind is purely a pale shadow of the body, so an epiphenomenon, having no independent powers but being completely subservient to the actions of the body), parallelism (where the mind and body run along completely parallel tracks,again in a completely unknown manner, but leading miraculuously to the synchrony between inner experiences and related bodily actions we observe in ourselves and others), and occasionalism (where mind and body occasionally hook up so as to produce the effects of mind on body or vice versa again as we experience, so being a limited form of parallelism).
One form of dualism is soul dualism, in which the soul is a part of the total human experience but continues after the death of the body. Such a feature was strongly represented in Ancient Egyptian religions, where the soul was considered as composed of several components, some of which died with the death of the body, others of which continued after the body's death. It is also a commonly held modern religious belief. Important names associated with dualism are Plato, Aristotle, Descartes, Bishop Berkeley, Kant, Hegel and Bertrand Russell amongst many others.
Idealism, on the other hand, supposes in short that mind is all that exists, and the whole world is so composed. However there are numerous nuanced varieties of idealism, some brought forward to avoid the difficulties of other versions.The extreme version that all is mind is usually called subjective idealism or phenomenalism, whilst objective idealists propose that thought is the highest degree of reality. On the other hand another branch of idealism, that of pansychism, consider that all objects of experience have minds; even more extremely, epistemological idealists claim that minds are aware of or perceive only their own ideas, not external objects.
Physicalism, at the other extreme, proposes that all of the Universe is composed of physical objects, and that even mind itself is created by some extremely subtle (and as yet unknown) mechanism of action between suitable physical components, most likely (according to modern ideas) situated in the brain. As for the other approaches to the mind-body problem expounded briefly above, there are numerous different varieties of physicalism: supervenience (where a given local distribution of matter cannot give rise to two different global patterns that are assumed to be instances of mind; this is to be regarded as a minimal form of physicalism), token and type (where the former assumes that for every particular event it can be identified with a purely physical event, the latter that every property is identical to a physical property), reductive and non-reductive physicalism (where the former involves a variety of assumptions on the manner in which statements of mental experiences are true if and only if some corresponding physical statements are true, whilst the latter is of the form of supervenience, for example, making no such strong assumptions), a priori versus a posteriori (where the claim of physicalism that all states of the world, including mental ones, can be derived from physical states, is given a priori or independently of experience, or alternately is a posteriori, so based on facts), and physicalism versus emergentism (where in the latter there is new knowledge emerging as mental states, such as described by psychology, for example, from underlying physical activity; more generally the mental is proposed to arise through an emergent process from underlying physical activity in matter).
Having given a brief survey of this variety of solutions to the mind-body problem that have been mulled over in the past, let us turn to what modern science has brought to the table to indicate how different the problem looks now, and what difficulties are presently faced by any proposed solutions.
The new knowledge base
The knowledge base we can bring to attempt to solve the mind-body problem has changed enormously over the thousands of years of the problem's existence. Matter has been probed down to very short distances through the development of ever higher-energy particle accelerators, so that we now have an understanding of matter in terms of the gauge theories unifying the electromagnetic and weak forces and further fusion with the strong nuclear forces by means of the quark-gluon gauge theory. Together with gravity, understood through Einstein's general relativity, the comprehension of matter has improved down to distances of about seventeen orders of magnitude. This year (2008) this distance will decrease even more by the coming on-stream of the large hadron collider, the LHC, at CERN. Hopefully it will find support for the basic features of the present level of unification, in terms of the discovery of the Higgs boson (as the basis for mass in the Universe) as well as providing us with new clues as to the next steps of probing ever deeper into the material world, such as by finding supersymmetric partners (or even supergravitational partners) to the present spectrum of elementary particles (for which there are even now claimed bumps in particle processes best explained, it has been claimed by their discoverers, by these exotic possibilities).
This progressive and impressive unlocking of the secrets of matter has only recently begun to be caught up by new ideas and new tools in brain science. These have allowed an ever better understanding of the manner in which the brain creates and controls experience. This knowledge is allowing ever deeper appreciation of how defects in brain processing brought about by various sorts of damage to the brain can enormously modify the overall experience of the person. There is still a large distance to travel to bring the knowledge of the brain up to the level of our enormously more detailed understanding of matter. But that gap appears to be closing fast, with a possible hiatus in the physics of the elementary particles due to the presently intractable character of the mathematics of superstrings (the only way known to sensibly unify gravity with the other forces of matter, Taylor et al, 1992); no such hiatus appears in brain science, except, of course, for the mind-body problem. Will that be the rock on which neuroscience founders in a similar way, it is claimed by some physicists, as that of unifying the forces of nature will similarly founder on the rock of full unification of the forces of nature?
The tools of brain science have been put to good use in probing the brain both locally and globally. The machines of PET and fMRI, measuring changes in blood flow in local regions of the brain due to neural activity, and EEG and MEG, measuring the electric and magnetic activities related more directly to neural activity in the brain, are allowing an increasingly precise view of the networks active across a range of functions. Combined with trans-cranial magnetic stimulation, the timing of the flow of crucial activity across the functional networks in the brain are beginning to give up their secrets. At the same time correlated activities of small groups of single neurons in different regions of the brain are indicating how these various regions process activity at a local level, but as part of a larger network of such regions in interaction. Ideas from dynamical systems theory have begun to help us understand better the brain at this intermediate mesoscopic level. In all, brains are becoming ever more understandable across all scales.
The major problem arising from this for the various idealist solutions outlined in the previous section to the mind-body problem are now clear: how can such precise physicalist explanations as have now been developed of the physical world at both micro and global scale be obtained from a purely mental universe? Mind does not enter into any of the detailed physical models (such as Einstein's Theory of General Relativity, or the Standard Model of elementary particles based on quantum field theory). The problem is as to how to derive such well-established theories from a mental approach to the universe. As far as this author knows, there is not even a framework available to attempt to solve this problem.
Can a non-material entity ever make any sense?
There is a further problem about the mind side of the Mind-Body problem which the enormous advances of high-energy physics and brain science, described above, have exacerbated, weighing the scales ever more heavily on the side of matter: How can any scientific discussion ever be given of an entity which is non-material? This question is not one to be taken lightly. Firstly if it is responded that science is in any case not the relevant arbiter here, then the whole discussion is going to be unable to make any forward progress to resolve any of the important issues (such as how mind and matter interact in any dualistic theory). Only by appeal to the world of experience can we conclude an argument between opposing positions. If it is claimed that part of that experience is in any case mental, so above the scientific arena, we can only point to the powerful developments in brain science that depend on inner report of subjects but ties them down to the activities of specific parts of the brain (or their absence in the case of deficit studies). Thus inner experience is used in a scientific manner here. Even the distortions of schizophrenics and those with other mental diseases are presently being used to probe those brain components, such as the attention system, which are damaged in the diseases, and may help explain the distorted experience.
The second more important point to consider is as to any possible answer to the question itself. Take any non-material entity. Can the entity possess any property enabling it to be observed in any scientific fashion? The range of scientific observations can cover the whole spectrum of all scientifically-known radiations, from those of light to those of radioactivity (using the W-bosons, observed at CERN), to those of the glue of the nuclear forces, using the so-called gluons observed indirectly at a number of particle accelerators, to those of gravity (using the gravitons, observed indirectly in double pulsars). But these observations would involve some material property, possibly very esoteric, but still a material property. So the answer to the question I raised is no.
At this point it is usual for the interlocutor to step back and say that science has not observed all possible aspects of the Universe. 'There are more things under heaven and earth,... etc, etc'. But there are not if they are of a material nature. It all fits together so remarkably accurately down to those incredibly short distances of seventeen orders of magnitude mentioned earlier that there can be nothing material that has been missed. Granted dark matter and dark energy are still not understood, although they could fit well into the new zoo of particles I mentioned earlier that may be seen at the LHC, and in any case were involved at a very very early stage of the Universe. They are not relevant to us here and now at the sorts of energies and sizes of objects we can normally deal with.
The simplest aspect of the problem of even discussing a non-material entity is that it could possess no possible attributes enabling it to be compared to anything else. It has no shape or length, no weight, no colour, or any other attribute that can be compared with any other entity. In other words it can only be made of indescribable attributes. It could be claimed that it must therefore be somehow composed of purely abstract attributes. But what could these be? Even purely mathematical symbols must have some quantitative ground to be made sense of. Abstract concepts such as love (used much in attributions to God in religions across the world) is itself suspect as to its meaning. If it is to be used in relation to our human interpretation then it is quantifiable (I love you very much), due to its basis in bodily processes and behavioural responses to the loved one. It is thus not immaterially based. If it has no such relation then the name does not help. This is so for all similar attributes with any human basis. But then we end up with attributes which can only be defined outside our experienced universe, so completely outside our ken.
Thus it is difficult to analyse any non-material entity in a useful manner. Given that the entity cannot be described in any quantitative manner at all, nothing can be said about it that can be agreed or disagreed about with any possibility of truth (where by the latter I mean by checking up on the statement). Non-material entities or components are thus very slippery ones which twist and turn between your fingers so strongly that they escape you before you have had a time to investigate them in any reportable manner. But if you cannot report on the nature of these entities then you cannmot even usefully discuss them. Even with yourself. But if you cannot do even that then such entities cannot be part of any useful conversation (with others or with yourself): no progress can ever be made in probing them.
The overall conclusion of this is that idealism and dualism face difficult problems, which presently have not been solved. We thus turn to physicalism, which has its own hard problems, and most particularly the hard problem of providing a detailed explanation of how mind can be created by suitably subtle dynamics of matter (Chalmers, 1996) and of crossing that seemingly unbridgeable gap between mind and matter (Levine, 1983). This is still unsolved in a universally accepted manner, but various promising approaches have been developed over the last few decades. These involve the reduction of the mind to the dynamics of brain activity involving some, if not all, of the billions of nerve cells in the brain. We will consider this at a functional level, so do not explore building up to that from the lower single nerve cell level (which however is increasingly effectively being achieved). So we turn to look at possible global principles for the brain - its crucial functional components.
Global principles of the brain's action
An important part of this understanding is that of the extraction of basic principles at a global level to help comprehend the awesome power possessed by these coupled circuits of local nerve cells (for references to the brain's capabilities and structure see the references at the end of this article on General references on the neuroscience of brain and mind). Several global principles can be extracted from the welter of possibilities. Three of these are arguably the most important:
- Attention, as a control system to filter lower-level brain activity so as to allow very few stimulus representations to enter the higher-level arena of thought and manipulation of neural activities; these filters are mainly in parietal and pre-frontal cortices. Attention thereby allows the higher level processes such as thinking and reasoning to work on a much smaller number of stimulus representations;
- Emotion, in terms of value maps learnt in orbito-frontal cortex (and also coded in associated amygdala sites) so as to bias what is to be processed and to guide choice of task goals (by their associated predicted rewards). These value maps, fused with body activations and automatic brain-stem responses, are used to give emotional value to decisions for action;
- Long-term memory created on-line, so as to allow for incremental wisdom about the environment for use as a guide for further interactions.
Other global principles can be added to these three possibilities, such as the use of hierarchical processing (as noted especially in vision, so as to create flexible visual codes for complex objects which can be used at a variety of scales). Another possibility involves the use of synchronization of neurons over long distances, such as at 40Hz and other frequencies, so as to solve the binding problem of combining the different codes for objects (as occur in multi-modal hierarchical coding schemes described earlier).
Global principles of the mind's action
In order to make progress on how the conscious mind is created by brain activity, we must also outline what it is we consider is the main structure of the mind. This is a highly controversial area, with many possible suggestions. However a certain degree of clarity seems to have arisen from recent ideas about the bipartite nature of consciousness by Western phenomenologists (Zahavi, 1999, 2005b, 2006). From this increasingly influential body of writing, consciousness can be seen to be divisible into 1) Content. This is available for report and internal manipulation, being composed of the colours, hardnesses and so on of objects, for example of the specific scent of the rose and the taste of the wine, and more generally of the various modality-based features of external objects in our consciousness; 2) Ownership. This is termed by Western phenomenologists the pre-reflective or inner self. The inner self is to be regarded as that denoted by the singular I. The inner self is supposed to have no content, the term pre-reflective implying that it is at a more primitive level than any reflective descriptor of oneself, such as possessing a beard or moustache or being blond. The pre-reflective self is required to be present in the mind as an independent entity along with content in order to prevent an infinite regress which would otherwise arise when considering I as defined by reflection on one's characteristics (Shoemaker, 1968). Thus although the pre-reflective self is content free it is an essential companion to the content of experience: without an owner there can be no content, no-one to have the experience. This aspect has been especially emphasised by the French philosopher Merleau-Ponty (Merleau-Ponty, 1945) where he noted that the word consciousness has no meaning independently of the pre-reflective self. Sartre (Sartre, 1943) also pointed out that the pre-reflective self constitutes the very mode of being of experience. It provides the bedrock of 'what it is like to be' in terms of ownership of the contents of experience; I am the experiencer (Nagel, 1974). Such a view is also supported by Western philosophers such as (Flanagan, 1992) who points out that a form of low-level consciousness (identifiable with the pre-reflective self) involves crucially experiencing an experience as mine (so as being the owner of the experience). A further aspect of the pre-reflective self accepted by these thinkers is that it is a constant and immediate component of consciousness, present "whenever I am living through or undergoing an experience" (Zahavi, 2005b, p1; ibid, 2006).
We should note here that this new component of consciousness, the pre-reflective self, was missed by the influential British philosopher David Hume (Hume, 1739) who searched for it in his own inner experience but could not find 'other than a bundle of sensations'. He did indeed find these sensory experiences to be identifiable as his own, but failed to notice that he also had an experience of ineffable ownership of them, one not identifiable with any sense experience. The ownership he was sure of, but ignored, was thus an intrinsic part of his experience, but one with "an immediate experiential givenness" as Zahavi puts it (Zahavi, 2006, p5). A similar mistake was made by a later British philosopher Gilbert Ryle (Ryle, 1950) as is evident by the title of his magnum opus The Ghost Within the Machine. His claim that there is no ghost, as would correspond to the pre-reflective self, was based on linguistic analysis that is contradicted by one's own experience, again as being sure of being owner of one's experiences. The component of one's conscious experience providing such surety is subtle indeed, as we see from its minimal function and problem of interaction with the content of experience, but it is not a ghost as being illusory, as Ryle claimed. Simlarly such an extra component of one's consciousness was missed by Brentano (Brentano 1874) who had influentially claimed that consciousness was always consciousness of, never just consciousness. But now the claim is that both sorts of consciousness exist.
We should also note that in a recent influential recent book (Metzinger, 2004) the author strongly claimed, as the tite of the book indicates, that there is no inner self or ego. However such an egoless model is apparently contradicted by the careful and valuable dissection of consciousness developed by the author in his book; this is carefully adumbrated in (Zahavi, 2005a). Thus the No-Self of the book's title should be considered as the component of consciousness missed by David Hume, Gilbert Ryle and Brentano, being the pre-reflective self.
The manner in which these two components of consciousness - content and pre-reflective self - can interact is highly problematic. It was not resolved by the phenomenologists, who seemed to take the majority view that the pre-reflective self arose from the body. That is also a highly controversial position, with the danger that subjects who have lost proprioception would lose their inner self; this is known not to happen, so making that position suspect (Cole & Paillard, 1995). Also sufferers from Cotard's syndrome (where the subject claims they are dead or missing their blood or internal organs, in association with depression or suicidal tendencies) provide further contrary empirical evidence(Metzinger, 2004). Such patients have at least loss of a body image and of emtional content (related to their depression) but more extremely may no longer use I to talk about themselves: they appear to be losing their pre-reflective self. This appears to be independent of the loss of body image. This question is also discussed more generally, in terms of experimental evidence for or against the existence of a possible preflective mental state involving proprioceptive feedback, in (Taylor, 2007). However in (Damasio, 2000) evidence is presented that loss of the body image does cause a loss of phenomenal consciousness. Yet any body-based self crucially does not have the automatic property of 'immunity to error through misidentification of the first person pronoun' (Shoemaker, 1968), regarded as a crucial component of consciousness. The phrase denotes the fact that I cannot sensibly ask you 'Are you sure it is you in pain?' when you tell me you are feeling pain: you just know it is you. Thus the problem of understanding how content and owner can interact is still open, and in some ways can be seen as hard as that of explaining consciousness more generally. However it has reduced the task to something more specific in terms of the supposed two components of consciousness.
Yet the problem of understanding how the owner of conscious content becomes aware of that content is decidedly non-trivial. This is partly because the owner or I is itself not properly understood. It is possible to consider the nature of the I as expounded in the writings of Eastern meditators. They have spent decades meditating on the nature of their inner self, and have built up a vast literature on their experiences across a range of disciplines, such as Zen and so on. However this material, whilst potentially very valuable, is also solely descriptive and highly personal. This makes it difficult to relate it to modern brain science. The increasing number of brain imaging experiments performed on meditators is gradually helping to bridge this gap, so that this vast literature from meditators could ultimately help exploration into the inner self. This process was also helped by the work of (Varela, 1996) who gave an initial attack on the brain basis of meditation; a further discussion is given in (Taylor, 2002), where an attention-based neural model was proposed of the pre-reflective self and how it could explain the mechanism of the pure conscious experience reported by meditators.
This bipartite division is now increasingly being accepted as an important avenue to attack mental disease, especially schizophrenia (Sass & Parnas, 2003). The distorted mental experiences reported by patients and occurring as a major part of the disease are now being seen, through a broad sudy of many sufferers, as arising from an imbalance between these two components of consciousness. Thereby an important brain basis for this two-component approach is being built which should strengthen and test it considerably.
Another influential bipartite division of consciousness was introduced in (Block, 1995). This proposed the two components of consciousness as being phenomenal consciousness and access consciousness (P and A for short respectively, as used by Block). P consciousness is just experience, granting the subject the experience of 'what it is like to be' (Nagel, 1974). Thus a P-conscious state is an experiential state. One function of P consciousness was suggested as integrating the outputs of specialised sensors and feeding the results to the executive system. On the other hand A consciousness involves states that are poised for use as a premise in reasoning and for rational control of response.
There has been much debate of these two different bipartite approaches to consciousness, although little attempt to compare and contrast them. It is clear that they are quite different ways of slicing up experience. Thus both P and A consciousness possess content, so that these have been fused together by the Western phenomenologists. However the owner of experience postied by the Western phenomenologists does not appear in its present no-content guise anywhere in the P-A split of (Block, 1995). The latter would thus seem to be vulnerable to the infinite regress of (Shoemaker, 1968). It is also to be emphasised that the owner or pre-reflective self may best be regarded as agency-free (Taylor, 2002). Thus the owner cannot initiate any action, except that of standing as the guardian at the gate to consciousness, to prevent any incorrect intrusion of a distracter into consciousness and provide the important feature of 'Immunity to error through misidentification of the first person pronoun' (Shoemaker, 1968). This phrase describes the feature that I know if I am in pain; you cannot ask me "Are you sure it is you who is in pain?"
The question of the relation of ownership to agency needs to be considered further, since the experience of agency ('did I cause the movement or did he/she?') and its possible defects have been seriously proposed as the basis of schizophrenia, for example (Frith, 1992). This appears to contradict the suggestion made earlier that such deficits arise from an imbalance in the relation between the owner and what is owned (the content). There have been several useful discussion of agency in action, such as in (Gallagher, 2000), and its possible breakdowns as might appear in schizophrenia. If however there is an attention basis for the owner/content consciousness system, then there is no agency here. This is known from discussions going back to William James. As Bricklin pointed out (Bricklin, 1999, p92) "Nothing in James' paradigm suggested that the predominance of consciousness of one thought over another was generated by the power of attention; rather the predominance in consciousness was itself attention".
This lack of agency of attention can be seen more clearly by the experimentally-based deconstruction of the attention control system into a goal-biasing system guiding the movement of the focus of attention, itself generated by a further control module, sending a signal back down into lower leve4l posterior cortices. This bias is what causes the movement of attention and that itself is fed by values of goals, stored elsewhere. Moreover, as pointed out in (Taylor, 2002) there is the added danger that if there were agentive experience in attention movement then there would be danger of an infinite regress. This would arise on exploring the source of the consciousness attributed to the attention mover.
In conclusion there is an important difference between agency ('I caused it') and ownership ('it was my thought'). Both may break down in schizophrenia, leading to a range of possible symptoms and distortions of experience. These are thought to be explicable along the Western phenomenological division of consciousness (Sass & Parnas, 2003); a similar explanation along the P-A division is not presently available.
There are numerous other ways of slicing up consciousness, some of which will undoubtedly help in clarifying what it is that any brain-based model must explain about the complexity of consciousness. For example the popular Higher Order Thought model (Rosenthal, 1997)supposes that a thought becomes conscious by having a higher order (not necessarily conscious thought) focus on it. This also has a danger of the infinite regress when it comes to defining the self, as do other single-component approaches to the mind. It would seem presently that only by identifying a separate part of consciousness as the inner self can the infinite regress be halted.
Attacking the mind-body problem
We have seen that there are serious problems in the idealist or dualist answers to the mind-body problem. However there are likewise serious problems for the physicalist approach: the Mind-Body problem still faces brain science and philosophy like a nemesis. Neither the global principles described earlier for the brain nor any additional ones seem to involve any solution to this problem. That is because they do not explicitly state how and where consciousness arises in the higher-order brain processing achieved by attention and guided by emotion and long-term memory. More particularly they do not give any handle at all on the neural components that could support the I at the core of one's self-attribution (for the Western phenomenologists owner/content division).
If the mind-body problem cannot be given a satisfactory solution through a brain-based approach as above, possibly expanding on the principles governing the brain, but always being able to be checked by scientific methods, then science itself will have failed in its attempt to explain all of the world. It would not have been able to answer in particular how mental experience is created from the activities of the apparently mindless nerve cells in interaction in the brain.
But such a dramatic situation has not been yet met with. Brain science is in its infancy, and even the principles adumbrated above are controversial. That of the creation of consciousness by brain activity is even more so. Thus we are still not in a position where the scientific process towards solving the mind-body problem has been universally seen to have failed, and only a dualistic solution (with mind in some non-physical space, whatever that means) would somehow have to be considered.
When we turn to falsifiability as a criterion for putative solutions to the mind-body problem then we need to be more precise. What is is we are claiming about the relationship between the mental experiences of a subject and the neural activity going on in their brain? Just to look for active brain regions when conscious processing is occurring (which would be silent when such processing is not going on) does not properly tackle the problem as to the functionality of the network of neural modules observed. It is this last question, of functionality of the relevant consciousness creating networks of the brain, which deserves considerably more analysis than given heretofore. It naturally leads us to consider various attempts of modelling consciousness already presented, to see if we can build on them to create a viable mind-from-matter machine. We must also attempt to relate them to the global principles of the mind's action, as described briefly earlier. For example if we accept the Western phenomenologists two-component view of consciousness, we must attempt to discern those regions involved in creating conscious content and those involved with supporting the pre-reflective self.
Possible brain-based solutions to the mind-body problem
A range of brain-based solutions have been put forward to solve the Mind-Body problem. It is only through some such brain-based approach that scientific progress can be achieved, and therefore all such possible approaches are of importance to be considered most carefully. However there is only space here to briefly survey a few of these approaches:
40 Hz and competing coalitions
It was proposed originally (Crick & Koch, 1991) that observed gamma range neural activity (with frequency around 40 Hz) during conscious processing creates actively bound neural representations of objects, thus being the basis of consciousness. This proposal has had large popularity more recently, although it apparently cannot answer the question as to the source of the inner perspective in the conscious experience which we each possess. Moreover such synchronisation was also observed in anaesthetised animals. Yet the 40Hz activity is no doubt an important component in the overall picture, involving as it does a summary of a considerable amount of data indicating that synchronization of activity between various brain sites is an important component of brain processing and more specifically of consciousness across a range of frequencies.
The 40 Hz approach to consciousness has now been abandoned by Crick and Koch, who replaced it by the concept of neural coalitions (Crick & Koch, 2003) in which 'Consciousness depends on certain conditions that rest on properties of very elaborate networks' (Crick & Koch, 2003, p 124). What makes an elaborate network automatically create any conscious experience at all is not further spelt out, except in terms of indicating how attention may play a role in 'biasing the competition among nascent coalitions' (Crick & Koch, 2003, p 124). These are certainly only general ideas in this latest 'framework for consciousness', and especially there is still no hint of any attack by the authors on the inner or pre-reflective self.
Recurrence
Numbers of authors (for example Lamme, 2003, Pollen, 2007) have suggested that recurrent feedback (observed, for example in visual cortex) can produce the experience of consciousness. However some of these claims are very debatable and need to be considered more carefully.
Strong support for recurrence as crucial in brain processing more generally has arisen, for example, from (Spivey and Dale, 2004) who analysed how recurrent dynamics can lead to an explanation of results from various psychological paradigms involved in classification and language processing, for example (although some of the phenomena they discuss are also non-conscious). Recurrence has also been used as a basis for the continued activity in working memory buffers, as analysed in detail in numerous research papers (for example, Wang, 2001). Such activity has been considered crucial to the generation of conscious experience as providing reportability to other sites of the relevant material, as assumed by many psychologists (see references in Taylor, 1999). However this use of recurrent neural activity to support continued buffer working memory activity does not necessarily provide at the same time any hint as to how any inner perspective might arise in such processing. There is also the difficulty that there are numbers of sites where recurrence is crucial for function (such as hippocampus), but which can be removed without a consequent catastrophic failure of consciousness. But it is necessarily the case that recurrence is a crucial component of brain processing as observed by neuroanatomy and neurophysiology, so surely will play an important role in consciousness creation, even if not its sole cause.
Quantum models
These models have been proposed (Penrose, 1989) to avoid strictures about understanding consciousness in computer terms due to Godel's incompleteness theorem. Godel's thereom raises the difficulty that any computational system, if unextended, is unable to be employed to prove all statements in the system, even though we can apparently see these statements as true (outside the system). Thus our abilities, so the argument goes, are always beyond those of a computational system (as suggested to be used by the brain to create consciousness). It is suggested that instead some miracle of quantum mechanics or even of quantum gravity is present to enable the brain to go beyond convential computation. How this occurs has so far not been specified in enough detail to produce a testable model. Moreover yet again the inner perspective is seemingly completely absent from this approach, so it has not yet shed any light on the nature of the pre-reflective self.
Global workspace
This important approach proposes (Baars, 1997) that consciousness arises once neural activity accesses a global workspace of well-connected neural modules (involving at least prefrontal and parietal lobes). It is as if this activity has been written on a blackboard for all to see. Such a feature is by now standard in computer science, and the frontal cortices have been observed to possess the ability to support fast learning, corresponding to fast writing on it (Duncan, 2001). However Baars considers activity on the global workspace to be more active than passive, and is involved in the competitive processes involved in gaining access to the global workspace. This is close to the suggestions in the 'Adaptive Coding Model' of (Duncan, 2001) in which there are competitive processes on the prefrontal cortex to help guide attention selection (in posterior sites). The global workspace therefore has aspects of importance for any future theory of the global brain. However it has no specific mechanism to produce any inner perspective, but that could well be added by a more careful inclusion of attention in its full complexity to help lift the global workspace model to a fully testable version, and also to provide inclusion of some form of inner self.
Retinoid model
This theoretical model (Trehub, 1991, 2007) details the neuronal structure and dynamics of a system of brain mechanisms that can be taken as a brain embodiment of Baar's global workspace. An important feature of the retinoid model is that it provides an internal representation of the world from a privileged egocentric perspective. The retinoid system also includes a mechanism for selective attention and provides a neuronal cluster at the spatiotopic origin of the retinoid structure which serves as an innate pre-reflective core self in the larger cognitive brain system.
Trehub, A. (1991) The Cognitive Brain. MIT Press.
Trehub, A. (2007) Space, self, and the theater of consciousness. "Consciousness and Cognition".
Complexity of activity
The need for a certain level of complexity of the interaction of activity across the brain in order that consciousness can arise has been emphasised (Edelman & Tononi, 2000) by developments of analyses of brain activity of subjects in various actively conscious states. This is clearly also going to be an important aspect, since consciousness possess that inner complexity of information content as observed experimentally as well as from the inside. If it were to be allied with a more detailed inclusion of the three principles mentioned earlier (attention, emotion value and memory) there may be the beginnings of a viable model of consciousness.
Relational mind
This approach proposed (Taylor,1999) that mind arose from the comparison between ongoing activity and activated relevant past memories. Undoubtedly there is such memorial 'filling out' of present activity, for example to give meaning to our current experience. In spite of inclusion of memory and emotion, there was little hint as to how the inner self or perspective could arise; that could be by further more careful discussion of the way that attention (the missing element of the triumvirate of faculties suggested as a crucial basis for efficient brain processing) is to be incorporated into the whole (simplified) architcture of the brain suggested earlier.
Attention copy experience
Attention acts as a control system, and is now known to involve parietal and prefrontal regions involved importantly in creating attention control signals to feedback to lower level inputs. Arguing by analogy with motor control in the brain, it was suggested (Taylor, 2003, 2006) that there is a copy of the attention movement signal that is crucial in providing an early wake-up call for mid-level cortices to enable attended activity to enter awareness by attention amplification, at the same time inhibiting distracters. The detailed mechanisms for using this copy to boost access to awareness of the attended stimulus, at the same time inhibiting distracters, can help explain, given the interpretations of the model, the 'immunity to error of the first person pronoun' (Sheomaker, 1968), an important feature of experience emphasised by Wittgenstein. This is further supported by experimental results indicating that a stimulus representation in the process of accessing awareness can have an inhibitory influence on activity created by the attention movement copy signal of a putative distracter created around 200 msecs after the distracter stimulus input (Sergent et al, 2005). This model appears to be a little closer to inner experience than the others listed, although considerable work still needs to be done to fill it out satisfactorily.
There are other models that employ attention formally to help process information more efficiently, as in the GW model of Baars, or in the Competing Coalitions model of Crick & Koch, both mentioned above. However there do not seem to be any models presently available of the attention copy type, in which the copy signal is used directly to provide the experience of ownership, identified with that of I.
Prospects for a brain-based solution to the mind-body problem
We repeat again here that we are taking for mind the conscious component of it, and not the many activities of ongoing processing below consciousness. It is clear that we cannot ignore these unconscious processes, since out of them conscious experience will arise. Thus any final model (or class of models) seriously attacking the Mind-Body problem will have to take careful account of both the conscious and non-conscious activity that is ongoing in the brain.
There are numerous important features from the above models of consciousness that we must take forward to build a more complete model with some chance of success: attention as a filter and possible source of feature binding, activity coming into awareness when accessing sites of working memory, associated attention copy ownership, various forms of memory as crucial components to give content to awareness, synchronization as a possible additional source of feature binding for object representations, suitably complex interacting brain states, emotion values as giving the whole system value and source of drive, and so on.
Do these various components begin to look as if they could provide a basis for a suitably scientific theory of consciousness? This can only be achieved by a modelling-cum-experimental attack on the many paradigms and associated observations in which consciousness crucially enters, and based on models including the three main principles mentioned earlier and some or all of the features of the various models outlined above. Such phenomena include, for example, the attentional blink, the Stroop test, attention search and associated phenomena such as the Posner benefit paradigm, processing of subliminal inputs, the phenomenon of blindsight and numerous others. Only when all of these have been explained satisfactorily at a quantitative level by such a developed model can we begin to approach the final solution to the mind-body problem. Even then there will be enormous problems of interpretation. But there is still a long way to get to that point yet.
General references on the mind-body problem
- Block N, Flanagan O & Guzeldere G (eds) (1998) The Nature of Consciousness. Cambridge MA: MIT Press
- Brothers L (2001) Mistaken Identity: The Mind-Body Problem Reconsidered. New York: SUNY Press
- Carruthers P (2004) The Nature of Mind. London: Routledge
- Chalmers D (1996) THe conscious mind. Oxford: Oxford University Press
- Churchland PM (2007) History of the Concept of Mind. Ashgate Publishers Ltd
- Kim J (2005) The Philosophy of Mind. Westview Press
- Metzinger T (2004) Being No-One: The Self-Model Theory of Subjectivity. Cambridge MA: MIT Press
- O'Connor T & Robb D (eds) (2003) philosophy of mind. London: Routledge
- O'Hear A (1998) The Nature of Consciousness. Cambridge: Cambridge University Press
- Tye M (1995) Ten Problems of Consciousness. Cambridge MA: MIT Press
General references on the neuroscience of brain and mind
- Andrewes D (2002) Neuropsychology: From Theory to Practice. Psychology Press
- Bechtel W (2007) mental mechanisms: Philosophical Perspectives on Cognitive Neuroscience. Psychology Press
- Blackmore S (2003) Consciousness: An Introduction. London: Hodder & Stoughton
- Johnson MH (1997) Developmental Cognitive Neuroscience. Oxford: Blackwells
- Longstaff A (2005) Instant Notes on Neuroscience. London: Taylor & Francis
- Restak R (2003) The New Brain. London: Rodale Ltd
- Stirling J (1999) Cortical Functions. London: Routledge
- Ward J (2005) Student's Guide to Cognitive Neuroscience. Psychology Press
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Recommended reading
- Aleksander, I. (1997) Impossible Minds. London: Imperial College Press.
- Chalmers, D.J. (1996). The conscious mind: In search of a fundamental theory . Oxford University Press.
- Cotterill, R. (1998) Enchanted Looms. Cambridge: Cambridge University Press
- Crick, F. H. C. (1994) The Astonishing Hypothesis. London: Simon & Schister
- Damasio, A. R. (1994) Descarte's Error. London: Picador Press
- Edelman, G. M. (1992) Bright Air, Brilliant Fire. New York: Basic Books
- Freeman, W. J. (1999) How Brains Make up Their Minds. London: Weidenfeld and Nicolson
- Hurley, S. L. (1998) Consciousnes in Action. Cambridge MA: Harvard University Press
- LeDoux, J. (1999) The Emotional Brain. London: Phoenix Press
- Marcel, A. J. & Bisiach, E.(editors) (1994) Consciousness in Contemporary Science. Oxford UK: Clarendon Press
- Metzinger, T. (2003) Being No-One. Cambridge MA: MIT Press
- Ramachnandran, V. S. (1998) Phantoms in the Brain. London: Fourth Estate
- Rose, S. (2005) The 21st Century Brain. London: Jonathan Cape
- Taylor, J. G. (1994) When the Clock Struck Zero
- Taylor, J. G. (1999) The Race for Consciousness. Cambridge MA: MIT Press
- Taylor J. G. (2002) From Matter to Mind. Jounral of Consciousness Studies 9(4):3-22
- Taylor, J. G. (2006) The Mind: A User's Manual. Wiley: Chichester UK
- Weiskrantz, L. (1997) Consciousness Lost and Found. Oxford: Oxford University Press
External links
See also
Attention, Consciousness, Global workspace, Models of consciousness
