Advances InInterdisciplinary Researches to Construct a Theory of Consciousness

doi:10.4236/jbbs.2011.14031

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Journal of Behavioral and Brain Science, 2011, 1, 242-261

doi:10.4236/jbbs.2011.14031 Published Online November 2011 (http://www.SciRP.org/journal/jbbs)

Advances in Interdisciplinary Researches to Construct a

Theory of Consciousness

Pierre R. Blanquet

Club d’Histoire des Neurosciences, University P. & M. Curie, Paris, France

E-mail: pr.blanquet@free.fr

Received August 22, 2011; revised October 13, 201 1; accepted October 28, 2011

Abstract

The interdisciplinary researches for a scientific explanation of consciousness constitute one of the most ex-

citing challenges of contemporary science. However, although considerable progress has been made in the

neurophysiology of states of consciousness such as sleep/waking cycles, investigation of subjective and ob-

jective nature of consciousness contents raises still serious difficulties. Based on a wide range of analysis and

experimental studies, approaches to modeling consciousness actually focus on both philosophical, non-neural

and neural approaches. Philosophical and non-neural approaches include the naturalistic dualism model of

Chalmers, the multiple draft cognitive model of Dennett, the phenomenological theory of Varela and

Maturana, and the physics-based hypothesis of Hameroff and Penrose. The neurobiological approaches in-

clude the neurodynamical model of Freeman, the visual system-based theories of Lamme, Zeki, Milner and

Goodale, the phenomenal/access hypothesis of Block, the emotive somatosensory theory of Damasio, the

synchronized cortical model of Llinas and of Crick and Koch, and the global neurophysiological brain model

of Changeux and Edelman. There have been also many efforts in recent years to study the artificial intelli-

gence systems such as neurorobots and some supercomputer programs, based on laws of computational ma-

chines and on laws of processing capabilities of biological systems. This approach has proven to be a fertile

physical enterprise to check some hypothesis about the functioning of brain architecture. Until now, however,

no machine has been capable of reproducing an artificial consciousness.

Keywords: Models of Consciousness, Third and First-Person Data/Qualia, Neuronal Workspace,

Thalamo-Cortical Neurons, Artificial Intelligence

1. Introduction

By separating the immaterial mind and the material body,

Descartes (1596-1650) traced a dividing line between

two incommensurable worlds: the sp iritual and the mate-

rial world [1]. From this ontological dualism is born an

epistemological dualism according to which the material

must be known by science and the mind by introspection.

During the 18 th century, the definition of the mind started

to emerge with that of consciousness, recognized as in-

strument of knowledge of the world which surrounds us

as also of our interiority. Hume (1711-1776), for example,

defined the mind: “as an interior theatre on which all that

is ‘mental’ ravels in a chaotic way in front of an interior

eye whose eyelids would not blink” [2]. On the contrary,

the materialist philosophers of the 18th century will give

up the cartesian immaterial su bstance, but they will keep

the metaphor of the body-machine and will extend this

metaphor to all human functions, including thought. Far

from showing the immateriality of the heart, indeed, the

cartesian cogito would prove rather for La Mettrie (1709-

1751), Diderot (1713-1784) and Holbach (1723-1789)

that the matter can think. In this line of idea, transform-

ist/proto-evolutionist and darwinian theories of 18th and

19th centuries, by introducing the id ea of a biological ori-

gin of the man, introduced the vast field of investigation

of the “living matter” and the problem of “when” and

“how” of the mind [3].

However, it was necessary to await the arise of the psy-

chology in the mid-nineteenth century, so that conscious-

ness becomes the central object of a new discipline claim-

ing science and asserting its independence with regard to

philosophy. This introspective approach of mind domi-

nated the investigations of researchers such as Herman

von Helmholtz (1821-1894), Wilhelm Wundt (1832-1920)

and William James (1842-1910) [4-6]. In the end of the

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19th century, in his founder text for a phenomenology,

Husserl (1859-1938) exposed his thesis on the nature of

consciousness [7]. Following Brentano’s work, he adopted

the concept of intentionality and gave it a central role

concerning the transcendental ego. He taught that con-

sciousness is never empty: it always aims an object and,

more generally, the world. The ego always carries in it the

r e l at ionsh ip wi th the wor ld as in tens iona l aimi ng. Th e earl y

20th century saw the eclipse of consciousness from scien-

tific psychology [8,9]. Without denying the reality of sub-

jective experiences, the strategy of behaviorists was to

draw aside consciousness of the direct field of investiga-

tion and to regard the brain as a “puzzle-box”. They then

put “between brackets” the irresolute problems which en-

cumbered the psychology to study stimuli and answers,

i.e. behaviors which reduce the analysis to rigid relations

between inputs (stimuli) and outputs (movements). In the

1960s, the grip of behaviorism weakened with the rise of

the cognitive psychology [10,11]. However, despite this

re newed emphasis on expla ining cogn itive capacitie s such

as memory, perception and language comprehension, con-

sciousness remained a largely neglected topic until the ma-

jor scientific and philosophical researches in the 1980s.

Researches on the correlations between the identifiable

mental activities and the objectivable cerebral activities

succeeded the traditional questioning on the relation be-

tween the mind and the brain. They were approached by

neurophilosophers, neurobiologists and researchers in ar-

tif icial intellige nce as familiar with the epide miologic an d

ontological questions as with the methodologic and empi-

ric ones. My pu rpose here is to rev iew the ma in at tempts to

provide an adequate explanatory basis for consciousness.

2. Consciousness, a Challenge for Philosophy

and Science

2.1. Difficulties in Philosophically Tackling the

Problem of Consciousness

Traditionally, one supposed in philosophy of mind that

there was a fundamental distinction between the dualist

philosophers, for which there are two kinds of phenom-

ena in the world, the mind and the body, and the monist

philosophers, for which the world is made of only one

substance. Although dualism can be of substance, as Des-

cartes thought it, the majority of dualist philosophers cur-

rently adopt a dualism of property which admits that the

matter can have both mental and physical properties. Like-

wise , if the monism can be an idealism (in the sense of

the philosopher Berkeley), the totality of monist philo-

sophers in the present time are materialists. Dualism of

property asserts the existence of conscious properties that

are neither identical with nor reductible to physical pro-

perties, but which may nevertheless be instantiated by the

very same things that instantiate p hysical properties. The

most radical dualism is the “psychological parallelism”,

which seeks to account for the psychophysiological cor-

relations while postulating that the mental state and the

cerebral state correspond mutually without acting one on

the other [12]. A less radical version, “the epiphenome-

nalism”, recognizes the existence of causal influences of

br a in on the mental states, but not the reverse [13]. In con-

trast to dualism, the monism claims that everything that

exists must be made of matter. A modern version of ma-

terialism is the physicalism. One type of physicalist ma-

terialism is the radical current of thought called “elimi-

nativism”, which rejects the very notion of consciousness

as muddled or wrong headed. It affirms that the mental

states are only temporary beliefs intended to be replaced

by neurobiologic models of research [14]. Another form

of physicalist materialism is the thesis of the stron g iden-

tity. It affirms the existence of an internal principle of

control (the mental principle) which is anything else only

the brain: the mental is reducible with the biological

properties, which themselves are reducible with physics.

However, the thesis most commonly adopted is that of

functionalism. The functionalism has been proposed to

answer an intriguing question: how to explain, if the the-

ory of identity is admitted, that two ind ividuals can have

different cerebral states and nevertheless to have at one

precise time exactly the same mental state? The response

of functionalists is as follows: what there is identical in

the two different cerebral occurrences from the same men-

tal state, it is the function. Whatever the physical consti-

tution of the cerebral state, several mental states are iden-

tical if their relations are causal. For the functionalists,

the mental states are thus defined by their functional role

inside the mental economy of the subject [15].

To accept traditional dualism it is agree to make a strict

distinction between the mental and the physical proper-

ties. In other words, it is to give up the unified neurosci-

entific theory which one can hope for to obtain one day.

But to accept the solutions recommended by the physi-

calist materialism is worse still, because those end up

denying the obvious fact that consciousness has internal

subjective and qualitative states. For this reason, certain

philosophers tried to solve the problem, either by adopt-

ing a mixed theory, both materialistic and dualistic, or by

denying the existence of subjective states of conscious-

ness. David Chalmers, for example, adopted the first so-

lution. Chalmers is known for his formulation of the dis-

tinction between the “easy” problem of consciousness

and the single “hard” problem [16,17]. The essential differ-

ence between the easy problem and the hard (phenomenal)

problem is that the former is at least theoretically an-

swerable via the standard strategy of functionalism. In

244 P. R. BLANQUET

support of this, in a thought experiment, Chalmers pro-

posed that if zombies are conceivably complete physical

duplicates of human beings, lacking only qualitative ex-

perience, then they must be logically possible and subjec-

tive personal experiences are not fully explained by physi-

cal properties alone. Instead, he argued that consciousness

is a fundamental property ontologically autonomous of

any known physical properties. Chalmers describ ed ther e-

fore the mind as having “phenomenal” and “psychologi-

cal” aspects. He proposed that mind can be explained by

a form of “naturalistic dualism”. That is, Chalmers ac-

cepted the analysis of functionalists while introducing the

concept of consciousness irreducible into his system.

According to him, since the functional organization pro-

vides the elements of mental states in their nonconscious

forms, it is necessary that consciousness is added again

to this organization.

Other philosophers, on the contrary, claimed that clos-

ing the explanatory gap and fully accounting for subject-

tive personal experiences is not merely hard but rather

impossible. This positi on was most closely associated with

tha t , for example, of Colin McGinn, Thomas Nagel [18,19]

and Daniel Dennett [20]. In particular, Dennett argued

that the concept of qualia is so confused that it cannot be

put to any use or understood in any non-contradictory way.

Having related the consciousness to properties, he then

declared that these properties are actually judgements of

properties. That is, he considered judgements of proper-

ties of consciousness to be identical to the properties

themselves. Having identified “properties” with judgeme nts

of properties, he could then show that since the judge-

ments are insubstantial, the properties are insubstantial

and thence the qualia are insubstantial. Dennett conclude d

therefore that qualia can be rejected as non-existent [20].

For Dennett, consciousness is a mystifying word because

it supposes the existen ce of a unified center of piloting of

thoughts and behaviors. For him, psychism is a hetero-

geneous unit which combines a series of mental proc-

esses that one knows little about such as perception, pro-

duction of the language, training, etc…: we allot, with the

others and ourself, some “intentions”, a “consciousness”,

because our behaviors are finalized [21,22]. In other writ-

ings, Dennett defended an original th esis on the free will

[23]. For that, he rested on evolutionary biology, on cog-

nitive sciences, on the theory of cellular au tomata and on

memetics [24,25]. Taking the opposite course to the ar-

gument of those which say that evolutionary psychology,

together with memetics, implies necessarily a world de-

prived of any possibility of choice, Dennett estimated on

the contrary that there is something of special in the hu-

man subject. According to him, the theory of evolution

supports the selective advent of avoiding agents. These

agents have the capacity to extract information of the

environment to work out strategies in order to avoid the

risks and to choose the judicious behaviors. Now, the per-

formance of this capacity is much more important for the

man than for the animal because each human individual

memorizes an important quantity of social and cultural

informations. It is therefor e ab surd to conceive a linear de-

terminism similar to that of the “demon” of Laplace. For

Dennett, the free will must rather be designed like the cha-

ot ic determinism of a vast neuromimetic network, in which

informations received in entries are combined according

to their respective weights to give completely unfore-

seeable and nonreproducible, but non random, outputs.

2.2. Difficulties in Scientifically Tackling the

Problem of Consciousness

One of difficulties in scientifically tackling the problem

raised by consciousness comes from the obvious fact that

it is the originating principle from which are generated

the categories of the interpersonal world and the subjec-

tivity of each personal world. Consciousness is not a sub-

stance but an act in itself non objectivable; it escapes an y

from representation. What consciousness has disconcert-

ing, notes Edelman, it is that it does not seem to raise of

the behavior. It is, quite simply, always there [26]. An-

other difficulty comes owing to the fact that conscious-

ness is a Janus Bifron, in the sense that it has both on-

tology with the first-person perspective and ontology with

the third-person perspective, irreducible one with the other

[27]. It has a first-person perspective because the mental

states are purely subjective interior experiences of each

moment of the life of men and animals. Principal sorts of

firs t-person data include visual, perc eptual, bodily and emo-

tional experiences, mental imagery and occurent thoughts.

But consciousness has also ontology with the third-person

perspective that concerns the behavior and the brain pr-

ocesses of conscious systems [22]. These behavioral and

neurophysiological data relevant to the third-person per-

spective provide the traditional material of interest for cog-

nitive psychology. Principal sorts of third-person data in-

clude perceptual discrimination of external stimuli, inte-

gration of information to do with the across sen sory mo-

dalities, automatic and voluntary actions, levels of access

to internally repr esented information, verbal reportability

of internal states and differences between sleep and wake-

fulness. The problem to scientifically approach the con-

sciousness phenomenon is much more complex still be-

cause the first-person experience is common for qualia

(singular ‘quale’), intentionality and self-consciousness.

In troduced by Lewis [28], the term of qualia is either used

in contemporary usage to refer to the introspectively ac-

cessible phenomenal aspects of our mental live [29], or

used in a more restricted way so that qualia are intrinsic

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P. R. BLANQUET

properties of experiences that are ineffable, nonphysical,

and given incorrigibly [30], or still used by some phi-

losophers such as Whitehead, which admits that qualia

are fundamental components of physical reality and de-

scribed the ultimate concrete entities in the cosmos as

being actual “occasions of experience” [31]. Experiences

with qualia are involved, for example, in seeing green,

hearing loud trumpets or tasting liquorice, bodily sensa-

tions such as feeling a twinge of pain, feeling an itch,

feeling hungry, etc… They are also involved in felt reac-

tions, passions or emotions such as feeling delight, lust,

fear or love, and felt moods such as feeling elated, de-

pressed, calm, etc… [32,33]. Intentionality and qualia ne-

cessarily coexist in the generation of conscious states,

but the aspect “qualia” may be distinguished from the as-

pect “intentionality” insofar as the perception of an object,

the evocation of a memory or an abstract thought can be

accompanied by different affective experiences (joy or

annoys, wellbeing or faintness, etc…) [34].

3. Experimental Approaches to a Science of

Consciousness

3.1. Neurophysiological Studies of Neural

Networks and Neuro-Mental Correlations

There are two common, but quite distinct, usages of the

term of consciousness, one revolving around arousal or

states of consciousness and another around the contents

of consciousness or conscious states. States of conscious-

ness are states of vigilance (i.e., the continuum of states

which encompasses wakefulness, sleep, coma, anesthesia,

etc) with which attention is associated. They are cyclic

and can last several hours. In contrast, conscious states

(percept, thought, memory or subjective experiences such

as qualia) are not cyclic nor reproductible and can last

only a few minutes, seconds or sometimes milliseconds.

Conscious states are situated in a spatiotemporal context.

They may refer to the past or the future but are always

experienced in the present. They introduce the conscious

representations and, more or less explicitly, global models

of self, alter-ego and world. States of consciousness and

contents of consciousness offer therefore very unequal

difficulties to the neuroscientific investigation [35-37].

3.1.1. Neurophysiological Studies of States of

Consciousness

Considerable progress has been made during the last de-

cade in the neurophysiology of states of consciousness. In

particular, impressive progress has been made in the neu-

rophysi olo gical i nve sti gat io n o f stat es of vi gi l a nce. N ota bly ,

the molecular mechanisms of distinct sleep/wake cycles

have been thoroughly studied [38]. The neuroanatomical

systems, the cellular and molecular mechanisms, and the

principal types of neurotransmitters involved in these me-

chanisms for the most part have been identified. In par-

ticular, an important line of research has investigate the

arousal in altered states of consciousness, for instance, in

and after epileptic seizures, after taking psychedelic drugs,

during global anesthesia or after severe traumatic brain

injury. These studies demonstrate that a plethora of nuclei

with distinct chemical signatures in the thalamus, mid-

brain and pons, must function for a subject to be in a suf-

ficient state of brain arousal to experience anything at all.

In particular, sleep/wake cycles essentially depend on ana-

tomical system which comprises structures of brainstem,

thalamic and hypothalamic nuclei, and the nucleus of

Meynert. Awak ening into the vigilan t state correlates with

a progressive increase in regional cerebral blood flow,

fi rst in the b rai nste m and th ala mus, then in th e cortex wit h

a particularly important increase in prefrontal-cingulate

activation and functional connectivity [38,39]. Anesthetic,

sleep, vegetative state and coma are all associated with

modulations of the activity of this thalamocortical network.

Although most dreams occur in paradoxical sleep, the

neurobiological mechanisms of walkefulness and para-

doxical sleep are identical at the thalamocortical level; the

only difference between the two states is at the brainstem

level. What differentiates these states is the relationship

with the environment: walkefulness brings into play motor

and sensory interactions with the external world, while

the paradoxical sleep is relatively independent of the ex-

ternal world. Thus, deaming may be considered to be an

incomplete form of consciousness, uncontrolled by the

environment, mainly reflecting internal factors [38].

3.1.2. Neurophysiologic al Studies of Contents of

Consciousness

Contrary to the study of consciousness states, the study

of consciousness contents raises very many problems.

Much difficulties are due to the brevity and not very re-

producible nature of subjective experiences. In addition,

the mechanisms of conscious thoughts often result from

processes at the same time conscious and unconscious

which coexist and ev en interact (the language, for exam-

ple, brings into play the unconscious use of linguistic rou-

tines). To explain the contents of consciousness of the third-

person perspective, we need actually to specify the neural

and/or behavioral mechanisms that perform the functions

[27]. The availability of behavioral data is reasonably

straightforward, because researchers have accumulated a

rich body of behavioral data relevant to consciousness.

But the body of neural data that has been obtained to date

is correspondingly more limited because of technological

limitations [33,40]. To study neural mechanisms, resear-

chers use currently a variety of neuroscientific measure-

246 P. R. BLANQUET

ment techniques including brain imaging via functional

magnetic resonance imaging (fMRI) and positron emis-

sion tomography (PET) technology, single-cell recording

through insertion of electrodes, and surface recording

through electroencephalography (EEG) and magnetoen-

cephalography (MEG) [27,41,42]. However, though these

approaches seem quite promising, many experimental find-

ings proved to be not univocal results and must be com-

pare and integrate with findings obtained from other ap-

p roaches . For ex a mpl e, when one se e s a fac e th ere be mu ch

activities (for example, on the retina and in the early vi-

sual cortex) that seem explanatorily redundant for the

formation of the conscious percept of the face [37]. To

specify precisely the neuronal basis of such a conscious

perception, psychologists have perfected a num ber of tech-

niques (masking, binocular rivalry, continuous flash sup-

pression, motion-induced blindness, ch ange blindness, inat -

te ntional blindness) [43]. In this design, one keep s as many

things as possible constant, including the stimuli, while

varying the conscious percept, so that changes in neural

activation reflect changes in the conscious percept rather

than changes in the stimuli. For instance, a stimulus can

be perceptually suppressed for seconds of time: the image

is projected into one of the observer’s eyes but is invisi-

ble, not seen. In this manner, the neural mechanisms that

respond to the subjective percep t rather than th e physical

stimulus can be isolated, permitting the footprints of visual

consciousness to be tracked in the brain. In some per-

ceptual illusion experiments, on the contrary, the physical

stimulus remains fixed while the percept fluctuates. A

good example is the Necker cube whose 12 lines can be

perceived in one of tw o di fferent ways in dept h.

Contrarily to techniques used for studying the third-

person experiences, methodologies for investigating first-

person experiences (in particular qualia) are relatively

thin on the ground, and formalisms for expressing them

are even thinner. The most obvious obstacle to the gath-

ering of first-person data concerns the privacy of such

data. Indeed, first-person data are directly available only

to the subject having these experiences. To others, these

first-person data are only indirectly available, mediated

by observation of the subject’s behavior or brain proc-

esses. In practice, the most common way of gathering

data about the conscious experiences of other subjects is

to rely on their verbal reports. However, verbal reports

have some limits. Some aspects of conscious experience

(e.g. the experience of emotion) are very difficult to de-

scribe. Moreover, verbal reports cannot be used at all in

subjects without language, such as infants and animals.

In these cases, one needs to rely on other behavior indi-

cators. For example, if an individual presses one of two

buttons depending on which of two ways the creature

perceives a Necker cube at a time, this button pressing is

a source of first-person data. A second obstacle is posed

by the absence of general formalisms with which first-

person data can be expressed. Reseachers typically rely

either on simple qualitative characterizations of data or

on simple parameterization of ones. These formalisms suf-

fice for some purposes, but they are unlikely to suffice

for the formulation of systematic theories [27,33].

3.1.3. Appro a c hes to Res earch Animal C o nsc i ousness

There is now abundant and increasing behavioral and

neurophysiological evidence consistent with, and even

suggestive of, conscious states in some animals. This is

due to the fact that human studies involving the correla-

tion of accurate reports with neural correlates can pro-

vide a valuable benchmark for assessing evidence from

studies of animal behavior and neurophysiology of some

animals [44]. Relevant forms of report included analysis

of responses to binocular rivalry in the case of primates,

vocalization in the case of birds such as african grey parrots,

and coloration and body patterning in the case of cepha-

lopods such as Octopus vulgaris. Rhesus macaque mon-

keys, for example, were trained to press a lever to report

perceived stimuli in a binocular rivalry paradigm. The

results from these studies were consistent with evidence

from humans subjected to binocular rivalry and magne-

toencephalography. They suggested that consciousness of

an object in monkeys involves widespread coherent syn-

chronous cortical activity. Likewise, similarities have been

found among the functional circuitry underlying the or-

ganization and sequencing of motor behaviors related to

vocalization in birds and mammals capable of vocal learn-

ing. Much of the neural basis for song learning in some

birds was found to reside in an anterior forebrain path-

way involving the basal ganglia, in particular a striatal

neuronal area ressemblin g that presen t in the mammalian

striatum. These homologies were strongly suggestive of

neural dynamics that support consciousness in birds. The

case of cephalopod mollusks is much less clear. Indeed,

cephalopod such as Octopus possesses a large population

of sensory receptors (they communicate with a nervous

system containing between 170 and 500 million cells)

and numerous nucleus-like lobes in its brain. Its optic

lobe, containing as many as 65 million neurons, plays a

critical role in higher motor control and establishment of

memory. Moreover, a number of other lobes appear to be

functionally equivalent to vertebrate forebrain structures,

though their organization bears little resemblance to the

laminar sheets of mammalian cortex. Recently, laboratory

tests and observations in a natural environment showed

that Octopus is heavily dependent on learning, and even

might form simple concepts. This strongly suggested that

cephalopod mollusks have a certain form of primary con-

sci o usness [45].

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P. R. BLANQUET

3.2. Approaches to Build Artificial

Intelligence Systems

Artificial Intelligence has not been sparing of metaphors

concerning the functioning of the human mind [46]. In

1950, Alan Turing tackled the problem of computation-

alism by proposing its famous test to establish whether

one can consider a machine as intell igen t as a hu man [47] .

So far, however, no computer has given responses totally

indistinguishable from the human responses. It appears

that this computational cognitivism is limited insofar as

it is founded on the formal character of calculation (in

this case, to think is equivalent to pro cess data, i.e. to cal-

culate, to handle symbols). This neuroscientific ap proach

is not very different from that where computer simula-

tions and mathematical models are used to study systems

such as stomachs, planetary movements, tornadoes, and

so on. In contrast, connectionism equates thinking with

the operation of a network of neurons and argues that

every cognitive operation is the result of countless inter-

connected units interacting among themselves, with no

central control. The connexionnist networks are in general

adaptive and allow the study of mechanisms of training

[48,49]. Such an approach is based on the view that the

nervous system itself computes [50]. In this topic, new

research has particularly developed that consists in mak-

ing work equations put in darwinian competition thanks

to evolutionary algorithms inspired by the modeling of

certain natural systems (for example, the competition be-

tween the social insects in the construction of the nest)

[51-53]. These systems, which are generic population-

based metaheuristic optimization algorithms, are able to

solve problems using some mechanisms inspired by the

biological evolution such as the reproduction, mutation,

recombination and selection. The principle on which they

are founded consists in initializing a population of indi-

viduals in a way dependent on the problem to be solved

(environment), then to make move this population of ge-

neration in generation using operators of selection, re-

combination and change. Actually, a number of cyber-

neticians try to approach this difficult problem with sys-

tems multi-agents (SMA), or “Massively Multi-Agents”

[54-60]. An agent-based model is a class of computa-

tional models for simulating the actions and interactions

of autonomous agents (both individuals or collective en-

tities such as organizations or groups) with the view to

assessing their effects on the system as a whole. This model

simulates the simultaneous operation s and interactions of

multiple agents located in an environment made up of

objects which are not agents and nonlikely of evolution,

in an attempt to re-create and predict the appearance of

complex phenomena. The agents can thus substitute for

the programmer and even produce unexpected results. In

this vein of approaches, a novel area of great interest is

the construction of robotic organisms. One essential pro-

perty of neurorobots is that, like living organisms, they

must organize the unlabeled signals they receive from the

environment into categories. This organization of signals,

which in general depends on a combination of sensory

modalities (e.g. vision, sound, taste, or touch), is a percep-

tual categorization, as in living organisms, makes object

recognition possible based on experience but without a

priori knowledge or instruction. Like the brain, neuroro-

bots op erate according to selectio nal principles: they fo rm

categorical memory, associate categories with innate

values, and adapt to the environment [61].

An important problem arises however with these new

perspectives of research: any constructive and exhaustive

approach of artificial consciousness must define a system

which has access, as the human primary consciousness,

within the meaning of its own knowledge. To inv estigate

this question, as Owen Holland said it, the system must

be able simultaneously to produce an intentional repre-

sentation and the perception in its own organization of

this intentionally generated form; it must be self-aware

[62]. A question then becomes: when will a machine be-

come self-aware? Although an answer to this question is

hazardous, one can determine at least a plausible neces-

sary precondition without which a machine could not de-

velop self-awareness. Th is precondition derives from the

assertion that, to develop self-awareness, a neural netwo rk

must be at least as complex as the human brain. Recently,

an enormous project (Human Brain Project) was given

for objective, believing this could be achievable in as

little as 10 years time, to succeed in simulating the func-

tioning of the neocortex of mammals by means of the

fastest supercomputer architectu re in th e world, th e IBM ’ s

Blue Gene platform [63]. For the moment, one modelled

a single cortical column consisting of approximately 60,000

neurons and 5 km of interconnecting synapses, chosen

from about 15,000 experiments carried out in laboratory.

This Blue Brain project requires to reproduce in the fu-

ture the equivalent of the million functional units that

holds the neocortex. It should be however noted that this

project refers only to a necessary but not sufficient con-

dition for the development of an artificial consciousn ess.

Even if the machine becomes as skilled as humans in

many disciplines, one cannot assume that it has become

selfaware. The existence of a powerful computer equipped

with millions of gigabytes is not in itself sufficient to

guarantee that the machine will be a self-awareness intel-

ligence. Moreover, it remains to define the criteria which

will make possible to recognize that an artificial entity

has a conscious state. Indeed, the problem is not to know

if a machine suffers, but if it behaves “as if” it suffered

[64,65].

248 P. R. BLANQUET

4. Explanatory Theories of Consciousness

Explanatory theories of consciousness should be distin-

guished from the experimental approaches to phenomena

of consciousnesss. While the ide ntif ication of correlation s

b etween aspects of brain activ ity and aspects of conscio us -

ness may constrain the specification of neurobiologically

plausible models, such correlations do not by themselves

provide explanatory links between neural activity and con-

sciousness. Models of consciousness are valuable preci-

sely to the extent that they propose such explanatory links.

To days, one can arbitrarily classify the various approache s

to modeling consciousness into two categories: the theo-

ries making correspond certain functional modes of the

brain to the conscious activity, and the theories binding

the structure of neural networks to conscious activity .

4.1. Theories Making Correspond Certain

Modes of the Brain to the Conscious Activity

In this category, one finds mainly the phenomenological

approaches of Francisco Varela and Humberto Maturana,

the physics-based hypothesis of Stuart Hameroff and Ro-

ger Penrose, and the neurodynamical model of Walter J.

Freeman.

Model of Varela and Maturana. Varella, and his men-

tor Humberto Maturana, developed a model based on the

notion of autopoiesis [66-70]. Based on cellular life,

autopoiesis attempts to define, beyond the div ersity of all

living organisms, a common denominator that allows for

the discrimination of the living from the non-living. In-

side the boundary of a cell, many reactions and many

chemical transformations occur but, despite all these pro-

cesses, the cell always remains itself and maintains its own

identity. The con sequence is that the interaction between

a living autopoietic unit and a component of its environ-

ment is only dictated by the way in which this compo-

nent is ‘seen’ by the living unit. To characterize this very

particular nature of interaction, Maturana and Varela used

the term of “cognition”. In their theory, the environment

has its own structural dynamics but it does not de termine

the changes in organism. Although it can induce a reac-

tion in the organism, the accepted changes are determined

by the internal structure of the organism itself. The con-

sequence is that the environment bring s to life the organ-

ism and the organism creates the environment with its

own perceptory sensorium. It should be emphasize that

this thinking is clo se to certain european philosophies, in

particular to that of Merleau-Ponty [71]. To express this

proce ss of mu tua l cal ling in to ex ist ence, this co -eme rgence ,

this equivalence between life and cognition, Varela and

Maturana used the word of “enaction”. For Varela, the

mind as a phenomenology in action, viewed from either

the first- or the third-person perspective, can only be de-

scribed as a behavior literally situated in a specific cycle

of operation [72]. For him, the mind is not in the head, it

is in a non-place of the co-determination of inner and

outer [73]. There is no separation between the cognitive

act and the organic structure of life, they are one ; the

traditional cartesian division between matter and mind

disappears at the level of human cognition at which the

notion of consciousness appears. To signify that human

consciousness has its counterpart in the organic structure,

that there is no consciousness outside the reality of bod-

ily experience, Varela used the term of “embodiment”

[74]. We are therefore global dynamic processes, in dy-

namical equilibrium, emerging and acting from interac-

tions of constituents and interactions of interactions. In

this thesis, the brain level is o nly considered to contribute

to properties of conscious experiences. At the phenome-

nal level, the constitution of conscious moments implies

a high temporal integration of multiple contents emerging

in a transitory way. According to Varela, because of its

biophysical organization (its organizational closure), the

brain belongs to multistable dynamical systems, in which

eigenbehaviors are constrained by a landscape of multiple

non-stable attractors. There are however some methodo-

logical problem s in this theory. The fi rst is the ol d problem

that the mere act of attention to one’s experience trans-

forms that experience. This is not too much of a problem

at the start of investigation, because one has a long way

to go until this degree of subtlety even comes into play,

but it may eventually lead to deep paradoxes of obser-

vership. The second problem is that of developing a lan-

guage or a formalism in which phenomenological data

can be expressed. Indeed, the notorious ineffability of con-

scious experience plays a role here, because the language

one has for describing experiences is largely derivative

on the language one has for describing the external world.

The third difficulty lies in the failure, or at least the limi-

tations, of incorrigibility: judgments could be wrong.

Model of Hameroff and Penrose. For Stuart Hamer-

off and Roger Penrose, neurons belong to world of tradi-

tio nal physics, are calculable and cannot explain as a such

consciousness. They propo sed th erefor e a new physics of

objective reduction which appeals to a form of quantum

gravity to provide an useful description of fundamental

processes at the quantum/classical borderline [75-78].

Within this scheme, consciousness occurs if an appropri-

ately organized system is able to develop and maintain

quantum coherent superposition until a specific “objective”

criterion (a threshold related to quantum gravity) is rea-

ched; the coherent system then self-reduces (objective

reduction). This type of objective self-collapse introdu ces

non-computability, an essential feature of consciousness

which distinguishes our mind from classical computers.

249

P. R. BLANQUET

Objective reduction is taken as an instantaneous event

(the climax of a self-organizing process in fundamental

sp ace-time) [31]. In this model, quantum-superposed states

develop in microtubules subunit proteins (tubulins) within

the brain neurons. They recruit more superposed tubulins

until a mass-time-energy threshold (related to quantum

gravity) is reached. At this point, self-collapse, or objec-

tive reduction, abruptly occurs. One equares the pre-re-

duction, coherent superposition phase with pre-conscious

processes, and each instantaneous (and non-computable)

objective reduction, or self-collap se, with a discrete con-

scious event. Sequences of objective reduction give rise

to a “stream” of consciousness. Microtubule-associated-

proteins can “tune” the quantum oscillations of the co-

herent superposed states. The objective reduction is thus

self-organized, or “orchestrated”. Each orchestrated ob-

jective reduction event selects (non-computably) micro-

tubule subunit states which regulate synaptic/neural func-

tions using classical signaling. The quantum gravity thre-

shold for self-collapse is relevant to consciousness be-

cause macroscopic superposed quantum states each have

their own superposed space-time geometries. However,

when these geometries are sufficiently separated, their

superposition becomes significantly unstable and reduce

to a single universe state. Quantum gravity determines

thus non-computably th e limits of the instability. In sum,

each orchestrated objective reduction event is a self-se-

lectio n of spac e- ti me geometry coupled to t he br ain th rough

microtubules and other molecules. This orchestrated ob-

jective reduction provides us with a completely new and

uniquely promising perspective on the hard problem of

consciousness [77,78]. The model of Hameroff and Pen-

rose has received serious criticism, notably from certains

philosophers such as Rick Grush and Patricia Churchland

[79]. These authors pointed out that microtubules are

found in all plant and animal cells, and not only in brain

neurons. They also stated that some chemicals that are

known to destroy microtubules do not seem to have any

effects on consciousness and that, conversely, anaesthet-

ics act without affecting the microtubules. Another ob-

jection addresses one of the strengths of Penrose and

Hameroff’s model, which is, according to its authors, that

it can account for the unity of consciousness. Indeed, if

th is impression of human consciousne ss unity should prov e

to be an illusion, then explanation s based on non-locality

and quantum coherence would become irrelevant.

Model of Freeman. The work of Walter J. Freeman

was based mainly on electrophysiological recording of

the olfactory system of awake and behaving rabbits [80-84].

Freeman found that the central code for olfaction is spa-

tial. Although this had been predicted by others on the

basis of studies in the hedgehog, certain aspects of his

results were surprising. For example, Freeman showed

that the information is uniformly distributed over the

entire olfactory bulb for every odorant. By inference every

neuron participates in every discrimination, even if and

perhaps especially if it does not fire, because a spatial

pattern requires both black and white. He discovered that

the bulbar information does not relate to the stimulus

directly but instead to the meaning of the stimulus. This

means that the brain does not process information in the

commonly used sense of the word. When one scans a

photograph or an abstract, one takes in its import, not its

number of pixels or bits. The brain processes meaning as

in this example. He also found that the carrier wave is

aperiodic: it does not show oscillations at single frequen-

cies, but instead has wave forms that are erratic and un-

predictable, irrespective of odorant condition. In the the-

ory of Freeman, the chaotic activity distributed among

the neuronal populations is th e carrier of a spatial pattern

of amplitude modulation that can be described by the

local heights of the recorded waveform. When an input

reaches the mixed population, an increase in the nonlin-

ear feedback gain will produce a giv en amplitude-modu-

lat ion pattern. The emergence of this pattern is considered

to be the first step in perception: meaning is embodied in

these amplitude-modulation patterns of neural activity,

whose structure is dependent on synaptic changes due to

previous experience. Through the divergence and con-

vergence of neural activity onto the entorhinal cortex, the

pulse p atterns coming from the bulb are smoothed, ther eb y

enhancing the macroscopic amplitude-modulation pat-

tern, while attenuating the sensory-driven microscopic

activity. Thus, what the cortex “sees” is a construction

made by the bulb, not a mapping of the stimulus. Hence,

perception is an essential active process, closer to hy-

pothesis testing than to passive recovery of incoming

information. The stimulus then confirms or disconfirms

the hypothesis, through state transition s that generate the

amplitude-modulation patterns. Fin ally, through multiple

feedback loops, global amplitude-modulation patterns of

chaotic activity emerge throughout th e entire hemisphere

directing its subsequent activity. These loops comprise

feedforward flow from the sensory systems to the en-

torhinal cortex and the motor systems, and feedback flow

from the motor systems to the entorhinal cortex and from

the entorhinal cortex to the sensory systems. Such global

brain states emerge, persist for a small fraction of a sec-

ond, then disappear and are replaced by other states. It is

this level of emergent and global cooperative activity

that is crucial for consciousness. Freeman tackled also

the enigmatic problem of the nature of the free will. He

proposed that the man, entirely engaged in a project and

in permanent relation with the other men and the world,

takes his decisions in real time by implying all his body.

The perceived will as conscious is informed only with a

250 P. R. BLANQUET

light delay. Not deciding a behavior in progress, it only

takes action to modulate the various aspects of the vol-

untary decision an d to legitimate it taking into con sidera-

tion whole of significances which constitute the subject.

There are however some problems in this interesting

Freeman’s account [85]. The mechanisms of origine and

the control of gamma oscillations are not yet entirely

clear. As predicted by Freeman, during gamma oscilla-

tions an average lead/lag relation exists between local

excitatory and inhibitory cells. Now, recent analyses of

the cellular dynamics concluded that recurrent inhibition

from fast spiking inhibitory cells is largely responsible

for maintaining the rhythmic drive, but the role played

by excitatory processes in modulating or driving the os-

cillations remains undetermined. Since cortical networks

form a dilute and massively interconnected network, a

satisfactory explanation for gamma activity should ex-

plain the on set and offset of ga mma activity in relation to

events at more distant sites and at larger scale in the

brain. Without clarification of these mechanisms it re-

mains difficult to define the link of gamma activity to

storage, retrieval and transmission of information, and

between thermodynamic and cognitive or informational

perspectives.

4.2. Theories Binding the Structure of Neural

Pathways to Conscious Activity

In this second category of models, a first strategy consists

in being focused on the visual system. This approach has

been mainly studied by Viktor Lamme, Semir Zeki, David

Milner and Melvyn Goodale. A second stategy, based on

a more global neurophysiological approach, has been

mainly developed by Ned Block, by Francis Crick and

Christof Koch, and by Rodolfo Llinas, Antonio Damasio,

Jean-Pierre Changeux and Gerald Edelman. In spite of

some “overwhelming commonalities” among these theo-

ries, as Chalmers said it [17], nearly all of them have

given a major role to interactions between the thalamus

and the cortex.

4.2.1. First Str ate g y F ocusing on the Visual System

Model of Lamme. The Local Recurrence theory of Vik-

tor Lamme distinguished between three hierarchical types

of neural processes related to consciousness [86-88]. The

first stage involves a “feedforward sweep” during which

the information is fed forward from striate visual regions

(i.e., V1) toward extrastriate areas as well as parietal and

temporal cortices, without being accompanied by any

conscious experience of the visual input. The second

stage involves the “localized recurrent processing” dur-

ing which the information is fed back to the early visual

cortex. It is this recurrent interaction between early and

higher visual areas which leads to v isual experien ce. Th e

third and final stages consist of “widespread recurrent

processing” which involves global interactions (as in the

global workspace of Changeux) and extends toward the

executive (i.e., the frontoparietal network) and language

areas. This final step also involves the attentional, execu-

tive, and linguistic processes that are necessary for con-

scious access and reportability of the stimulus. An inter-

esting aspect of this theory is that it offers an explanation

for the difference between conscious and unconscious

perception in mechanistic rather in architectural terms.

Another interesting aspect of this theory, although pro-

vocative, is that consciousness should not be defined by

behavioral indexes such as the introspective reports of

the subject. Instead, on e should rely on neural ind exes of

consciousness, one of which is neural recurrence. Indeed,

Lamme is concerned with the question of defining phe-

nomenological consciousness when a report is impossible.

However, one main difficulty with this theory is that it

fails to take into account the recurrent connections that

exist between regions that are not associated with con-

sciousness (for instance between the area V1 and the tha-

lamus). Although it remains possible that consciousness

involves local recurrence between some cerebral com-

ponents, this processus cannot then be considered as a

sufficient condition for consciousness since it requires

the involvement of additional mechanisms for explaining

why it only applies to a restricted set of brain regions.

Model of Zeki. In the microconsciousness theory of

Semir Zeki, it is assumed that instead of a single con-

sciousness, there are multiple consciousness that are dis-

tributed in time and space [89,90]. This theory reflects

the large functional specialization of the visual cortex.

For example, while the perception of colors is associated

with neural activity in area V4, motion perception re-

flects neural activity in MT/V 5. Zeki took these findings

as evidence that consciousness is not a unitary and sin-

gular phenomenon, but rather that it involves multiple

consciousness that are distributed across processing sites,

which are independent from each other. Another evi-

dence in favor of this hypothesis is that the conscious

perception of different attributes is not synchronous and

can respect a temporal hierarchy. For example, psycho-

physical measures have shown that color is perceived a

few tens of milliseconds before motion, reflecting the

fact that neural activity during perception reaches V4

before reaching MT/V5. One main difficulty with this

theory is that any processing region in the brain should,

at first glance, constitute a neural correlates of conscious-

ness in the multiple-consciousness theory. As such, it

remains unclear why conscious perception is not associ-

ated with activity in most brain regions, including the

cerebellum and subcortical regions, especially those con-

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veying visual signals (e.g., the lateral geniculate nucleus).

Another difficulty for this hypothesis is that visual re-

gions can lead to the binding of several attributes in the

absence of consciousness. This has been shown, for in-

stance, in a patient with a bilateral parietal damage, sug-

gesting that the binding mechanisms that are supposed to

lead to microconsciousness can in fact operate in the

absence of con sci ousness.

Model of Milner and Goodale. The duplex vision

theory proposed by David Milner and Melvyn Goodale

postulates that visual perception involves two intercon-

nected, but distinctive pathways in the visual cortex, na-

mely, the dorsal and the ventral stream [91,92]. After

being conveyed along retinal and subcortical (i.e., geni-

culate) structures, visual information reaches V1 and

then involves two streams. The ventral stream projects

toward the inferior part of the temporal cortex and serves

to construct a conscious perceptual representation of ob-

jects, whereas the dorsal stream projects toward the pos-

terior parietal cortex and mediates the control of actions

directed at those objects. The two streams also differ at

the computational and functional levels. On the on e side,

the ventral stream conveys information about the endur-

ing (i.e., long-lasting) characteristics that will be used to

identify the objects correctly, and subsequently to link

them to a meaning and classify them in relation to other

elements of the visual scene. On the other side, the dorsal

stream can be regarded as a fast and online visuomotor

system dealing with the moment-to-moment information

available to the system, which will be used to perform

actions in real time. Recent evidence with visual masking

has revealed unconscious neural activity in ventral re-

gions, including the fusiform face area. This type of evi-

dence is problematic for the duplex vision hypothesis

since it predicts that conscious perceptions should be

proportional to neural activity in the ventral system. Such

a possibility of unconscious ventral processing can be

nevertheless accommodated by assuming a threshold me-

chanism, as proposed in the model of Zeki [90]. How-

ever, including this threshold leads the theory to lose it

former appeal, since consciousness is “only partially cor-

related” with activity in the ventral system.

4.2.2. Second Strategy Based on a Gl obal

Neurophysiological Approach

Model of Block. One of the most influential issue in

recent years has been the potential distinction between

phenomenal and access consciousness proposed by Ned

Block [93-95]. According to Block: “phenomenal con-

sciousness is experience; the phenomenally conscious

aspect of a state is what it is like to be in that state. The

mark of access-consciousness, by contrast, is availability

for use in reasoning and rationally guiding speech and

action”. In short, phenomenal consciousness results from

sensory experiences such as hearing, smelling, tasting,

and having pains. Block grouped together as phenomenal

consciousness the experiences such as sensations, feel-

ings, perceptions, thoughts, wants and emotions, whereas

he excluded anything having to do with cognition, inten-

tionality, or with properties definable in a computer pro-

gram. In contrast, access consciousness is available for

use in reasoning and for direct conscious control of ac-

tion and speech. Access consciousness must be “repre-

sentational” because only representational content can fi-

gure in reasoning. Examples of access consciousness are

thoughts, beliefs, and desires. A point of controversy for

this attempt to divide consciousness into phenomenal and

access consciousness is that some people view the mind

as resulting from fundamentally computational processes.

This view of mind implies that all of consciousness is

definable in a computer program. In fact, Block felt that

phenomenal consciousness and access consciousness nor-

mally interact, but it is possible to have access conscious-

ness without phenomenal consciousness. In particular,

Block believed that zombies are possible and a robot

could exist that is “computation ally id en tical to a person”

while having no phenomenal consciousness. Similarly,

Block felt that one can have an animal with phenomenal

consciousness but no access consciousness. If the dis-

tinction of Block between phenomenal and access con-

sciousness is correct, then it has important implications

for attempts by neuroscientifists to identify the neural

correlates of consciousness and for attempts by computer

scientis ts to produce artificial con sciousness in man-mad e

devices such as robots. In particular, Block suggested that

non-computational mechanisms for producing the sub-

jective experiences of phenomenal consciousness must

be found in order to account for the richness of human

consciousnesss, or for there to be a way to rationally en-

dow man-made machines with a similarly rich scope of

personal experiences of “what it is lik e to be in co nscious

states”. However, many advocates of the idea that there

is a fundamentally computational basis of mind felt that

the phenomenal aspects of consciousness do not lie out-

side of the bounds of what can be accomplished by com-

putation. Indeed, some of the conflict over the importance

of the distinction between phenomenal consciousness

and access consciousness centers on just what is meant

by terms such as “computation”, “program” and “algo-

rithm”, because one cannot know if it is within the power

of “computation”, “program” or “algorithm” to produce

human-like consciousness.

Model of Llinas. Rodolfo Llinas proposed a model in

which the notion of emergent collective activity plays a

central role [96-98]. He suggested that the brain is essen-

tially a closed system capable of self-generated activity

252 P. R. BLANQUET

based on the intrinsic electrical properties of its compo-

nent neurons and their connectivity. For Llinas, con-

sciousness arises from the ongoing dialogue between the

cortex and the thalamus. The hypothesis that the brain is

a closed system followed from the observation that the

thalamus input from the cortex is larger than that from

the peripheral sensory system, suggesting that thalamo-

cortical iterative recurrent activity is the basis for con-

sciousness. A crucial feature of this proposal was the pre-

cise temporal relations established by neurons in the cor-

tico-thalamic loop. This temporal mapping was viewed

as a functional geometry, and involved oscillatory activity

at different scales, ranging from individual neurons to the

cortical mantle. Oscillations that traverse the cortex in a

highly spatially structured manner were therefore con-

sidered as candidates for the production of a temporal

conjunction of rhythmic activity over large ensemble of

neurons. Such gamma oscillations were believed to be

sustained by a thalamo-cortical resonant circuit involving

pyramidal neurons in layer IV of the neocortex, relay-

thalamic neurons, and reticular-nucleus neurons. In this

context, functional states such as wakefulness or sleep

and other sleep stages are prominent examples of the

breadth of variation that self-generated brain activ ity will

yield. Since no gross morphological changes occur in the

brain between wakefulness and dreamless sleep, the dif-

ference must be functional. Llimas proposed therefore

that conscious processes of changes observed in the cy-

cle sleep/dream/awakening rest on pairs of coupled os-

cillators, each pair connecting thalamus and the cortical

region. He suggested also that temporal binding is gener-

ated by the conjunction of a specific circuit involving

specific sensory and motor nuclei projecting to layer IV

and the feedback via the reticular nucleus, and a non-

specific circuit involving non- specific in trala minar nuclei

projecting to the most superficial layer of the cortex and

collaterals to the reticular and non-specific thalamic nu-

clei. Thus, the specific system was supposed to supply

the content that relates to the external world, and the non-

specific system was supposed to give rise to the temporal

conjunction or the context. Together, they were consid-

ered as generating a single cognitive experience.

Model of Crick and Koch. In their framework, Fran-

cis Crick and Christof Koch tried to find the neural cor-

relates of consciousness and suggested the existence of

dynamic coalitions of neurons, in the form of neural as-

semblies whose sustained activity embodies the contents

of consciousness [99-101]. By cortex they meant the re-

gions closely associated with it, such as the thalamus and

the claustrum. Crick and Koch began their theory with

the notion of an “unconscious homunculus”, which is a

system consisting of frontal regions of the brain “looking

at the back, mostly sensory region”. They proposed that

we are not consciou s of our thoug hts, bu t only of sen sory

representations of them in imagination. The brain presents

multiple rapid, transient, stereotyped and unconscious

processing modules that act as “zombie” modes. This is

in contrast to the conscious mode, that deals more slowly

with broader, less stereotyped thoughts and respons es. In

this model, the cortex acts by forming temporary coali-

tions of neurons which support each other activity. The

coalitions compete among each other, and the winning

coalition represents what we are conscious of. These coa-

litions can vary in how widespread they are over the

brain, and in how vivid and sustained they are. Moreover,

more than one coalition can win at a given time. Espe-

cially, there might be different coalitions in the back and

in the front of the cortex, where the coalitions in th e fro nt

represent feelings such as happiness. An important point

in this model is that consciousness may arise from cer-

tain oscillations in the cerebral cortex, which become

synchronized as neurons fire 40 times per second. Crick

and Koch believed the phenomenon might explain how

different attributes of a single perceived object (its color

and shape, for example), which are processed in different

parts of the brain, are merged into a coherent whole. In

this hypothesis, two pieces of information become bound

together precisely when they are represented by synchro-

nized neural firing. However, the extent and importance

of this synchronized firing in the cortex is controversial.

In particular, it remains a mystery: why should synchro-

nized oscillations give rise to a v isual experience, no ma tt er

how much integration is taking place? It should be added

tha t, in this model, the neurons that are a part of the neural

correlate of consciousness will influence many other neu-

rons outside this correlate. These are called the penumbra,

which exists of synaptic changes and firing rates. It also

includes past associations, expected consequences of mo-

vements, and so on. It is by definition not conscious, but

it might become so. Also, the penumbra might be the site

of unconscious priming.

Model of Damasio. Antonio Damasio explored mainly

the complexity of the human brain taking into con sidera-

tion emotion, feeling, language and memory. According

to him, the more important concepts are emotion, feeling,

and feeling a feeling for the core consciousness [102,103].

The substrate for the representation of an emotional state

is a collection of neural dispositions in the brain which

are activated as a reaction on a certain stimulus. Once

this occurs, it entails modification of both the body state

and the brain state. This process starts as soon as the or-

ganism perceives, in the form of simple or complex sen-

sory messages, proprioceptive or behavioral indicators

meaning the danger or, on the contrary, the welfare. For

Damasio, the emergence of feeling is based on the cen-

tral role played by the proto-self that provides a map of

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the state of the body [102]. The neuronal patterns which

constitute the substrate of feeling arise in two classes of

changes: changes related to body state, and changes re-

lated to cognitive state. Thus, a feeling emerges when the

collection of neural patterns contributing to the emotion

leads to mental images. The feelings correspond to the

perception of a certain state of the body to which the

perception of the corresponding state of mind is added,

i.e. thoughts that the brain generates taking into account

what it perceives of the state of the body. The notion of

feeling is based on the organism detecting that the repre-

sentation of its own body state has been changed by the

occurence of a certain object [102]. Consciousness is

thus built on the ba sis of emotions transformed into feel-

ings and feeling a feeling ; it mobilizes and gathers con-

stantly, in a workspace, a certain number of informations

necessary to strategies of survival and decision making.

In this theory, consciousness is defined explicitly as a

state of mind in which there is knowledge of one’s own

existence and of the existence of surroundings. Accord-

ing to Damasio, the emotions generate three types of

levels of consciousness during the darwinian evolution:

pr otoself, core self, and oneself-autobiographical [102,104 ].

The protoself is the oneself most primitive and most wi-

despread within the alive species. It is constituted by

special kinds of mental images of the body produced in

body-mapping structures, below the level of the cerebral

cortex. It results from the coherent but temporary inter-

connections of variou s cerebral charts of reentries of sig-

nals that represent the state of the organism at a given time.

The protoself is an integrated collection of separate neu-

ral p atte rns t hat ma p mo me nt b y moment, t h e most s t a ble

aspects of the organism’s physical structure. The first

product of the protoself is primordial feelings. Whenever

one is awake there has to be some form of feeling. On a

higher level, the second form of the self, the core self, is

about action. Damasio said that the core self unfold s in a

sequence of images that described an object engaging the

protoself and modifying that protoself, including its pri-

mordial feelings. These images are now conscious be-

cause they have encountered the self. On a still higher

level there is the autobiographical self, constituted in

large part by memories of facts and events about the self

and about its social setting. It develops during social in-

teractions to form what Damasio called “the wide con-

sciousness”. That is, the protoself and the core self con-

stitute a “material me” whereas the autobiographical self

co nstitut es a “s ocial me”. Our sense of p erson an d iden tity

is therefore in the autobiographical self.

All emotions engage structures related to the repre-

sentation and/or regulation of organism state as, for ex-

ample, the insular cortex, the secondary somatosensory

cortex, the cingulated cortex, and nuclei in brainstem

tegmentum and hypothalamus [105]. These regions share

a major feature in that they are all direct and indirect

recipients of signals from the internal milieu, viscera and

musculoskeletal frame. Damasio considered that no man

can make decisions that are independent of the state of

his body and his emotions. The influences that he un-

dergoes are so numerous, that the assumption of a linear

determinism which would determine him is not defend-

able. Till now, most theories had addressed emotion as a

consequence of a decision rather than as the reaction

arising directly from the decision itself. On the contrary,

Damasio proposed that individuals make judgements not

only by assessing the severity of outcomes and their

probability of occurrence, but also primarily in terms of

their emotional quality [106]. The key idea of Damasio

was that decision making is a process that is influenced

by signals that arise in bioregulatory processes, including

those that express themselves in emotions and feelings.

Decision making is not mediated by the orbito-frontal

cortex alone, but arises from large-scale systems that

include cortical and subcortical components. Like Den-

nett and Freeman, therefore, Damasio asserted that the

individuals are under the influence of a chaotic causality

of processes imprédictibles, indescribable, nonreproduci-

ble, but not random. Two main criticisms have been made

about this theory [107]. First, Damasio tried to give an

account of the mind as a set of unconscious mapping

activities of the brain, and this did not presuppose, or at

least it did not obviously presu ppose, that these activities

are conscious. But it is hard to understand any of these

divisions of the self, protoself, core self and autobio-

graphical self without supposing that they are already

conscious. Second, Damasio stumbled over dreaming.

Although phenomenal consciousness can be very vivid in

dreams even when the rational processes of self-cons-

ci ousness are much diminished, Damasio described dreams

as mind processes unassisted by consciousness. He claime d

that wakefulness is a necessary condition for conscious-

ness. He described dreaming as paradoxical since, ac-

cording to him, the mental processes in dreaming are not

guided by a regular, properly functioning self of the kind

we deploy when we reflect and deliberate. However,

contrary to this point of view, it should be noted that

dreaming is paradoxical only if one adopts a model of

phenomenal consciousness based on self-consciousness

(on knowledge, rationality, reflection and wakefulness).

Model of Changeux. The model of Changeux, devel-

oped with Stanislas Dehaene and collaborator s [108,109],

is founded on the idea that cerebral plasticity is mainly

assured by a vast unit of interconnected neurons based on

the model of “global workspace”, historically related to

Baar’s cognitive model propo sed in the 1980s [110]. Re-

call that the global workspace model of Baar is a process

254 P. R. BLANQUET

which implies a pooling of information in a complex

system of neural circuits, in order to solve problems that

none of circuits could solve alone. This theory makes

possible to explain how the consciousness is able to mo-

bilize many unconscious processes, autonomous and lo-

calised in various cerebral regions (sensory, perceptuals,

or imply in attention, evaluation, etc…), in order to treat

them in a flexible and adjusted way [111]. Based on this

workspace theory, Changeux proposed that neurons dis-

tributed with long-distance connections are capable of

interconnecting multiple specialized processors. He also

proposed that, when presented with a stimulus at thresh-

old, workspace neurons can broadcast signals at the brain

scale in an all-or-none manner, either highly activated or

totally inactivated [108,112-114]. Workspace neurons thus

allow many different processors to exchange information

in a global and flexible manner. These neurons are as-

sumed to be the targets of two different types of neuro-

modulatory inputs. First, they display a constantly fluc-

tuating spontaneous activity, whose intensity is modu-

lated by activating systems from cholinergic, noradren-

ergic and serotoninergic nuclei in the brain stem, basal

forebrain and hypothalamus. These systems modify the

state of consciousness through different levels of arousal.

Second, their activity is modulated by inputs arising from

the limbic system, via connections to the anterior cingu-

lated, orbitofrontal cortex , and the direct influen ce of do-

paminergic inputs [115].

In this global workspace model, highly variable net-

works of neural cells are selected and their activity is

reinforced by environmental stimuli. These reinforced

networks can be said to ‘represent’ the stimuli, thoug h no

particular network of neural cells exclusively represents

any one set of stimuli. The environment does not imprin t

precise images in memory. Rather, working through sense s,

the environment selects certain networks and reinforces

the connections between them. These processes connect

memory to the acquisition of knowledge and the testing

of its validity. Every evocation of memory is a recon-

struction on the basis of physical relativel stable traces

stored in the brain in latent form [116]. Changeux and

Dehaene distinguished three kinds of neuronal represen-

ta t i ons: per cepts; ima ges, conce pts, and int entions ; and pre-

representations. Percepts consist of correlated activity of

neurons that is determined by the outer world and disin-

tegrate as soon as external stimulation is terminated. Im-

ages, concepts, and intentions are activated objects of

memory, which result from activating a stable memory

trace (similar to the “remembered present” of Edelman).

Prerepresentations are multiple, spontaneously arising

unstable; they are transient activity patterns that can be

selected or eliminated [117]. In this line of idea, though ts

can be defined in terms of “calculations on the mental

objects” [118]. To be cap able to be mobilized in the con-

scious workspace, a mental object must meet three crit er ia :

1) The object must be represented as a firing pattern of

neurons; 2) The active workspace neurons must possess

a sufficient number of reciprocal anatomical connections,

particular in prefrontal, parietal and cingulated cortices;

3) At any moment, workspace neurons can only sustain a

single global representation, the rest of workspace neu-

rons being inhibited. This implies that only one active cor-

tical representation will receive the appropriate top-down

amplification and be mobilized into consciousness, the

other representations being temporarily unconscious [119].

When a new situation happens, selection would occur

from an abundance of spontaneously occurring prerepre-

sentations, namely those that are adequate to new circum-

stances and fit existing percepts and concepts. The free

will is b ased o n this adap tatio n pro cess called ‘resonan ce ’,

because planning and decision making result from this

selective adaptation process [117]. As in evolution, this

could be a random recombination of representations. The

meaning of representations involved would be given by

their proper functions. Plans gen erated in this way would

be intelligible because they could be appropriate for the

situation. Naturally, linguistically coded representations

could therein also be of central importance. It results from

this global neurophysiological model that, as Changeux

said it, the identity between mental states and physio-

logical or physicochemical states of the brain is essential

in all legitimacy and that it is enough with the man to be

a neuronal man [118,120]. One important aspect that fol-

lows from this theory is that once a set of processors

have stated to communicate through workspace connec-

tions, this multidomain processing stream also becomes

more and more automatized through practice, resultin g in

direct interconnections, without requiring the use of work-

space neurons and without involving consciousness. An-

other important aspect of this theory is that information

computed in neural processors that do not possess direct

long-range connections with workspace neurons, will al-

ways remain unconscious. This global workspace model

has however been considered by some authors as a re-

strictive theory of access consciousness sacrificing some

phenomenological aspects of consciousness. In other terms,

it has been criticized for confounding the subjective ex-

perience of consciousness with the subsequent executive

processes that are used to access its content.

Model of Edelman. To explain the primary conscious-

ness, Edelman argued that living organisms must organize

into perceptual categorization the unlabeled signals they

receive from the environment. He started therefore his

model by proposing a hypothesis which describes the

fundamental process of categorization. This highly arti-

culated hypothesis is mainly based on the theory of neu-

255

P. R. BLANQUET

ronal group selection implying a basic process termed

‘reentry’, a massively recursive activity between neuronal

groups. It is also based on the fundamental concept called

“degeneracy”, whereby elements that are structurally dif-

ferent can perform the same function. The first idea of

Edelman was to use the assumption of tying, imagined

by Francis Crick for visual perception [22], to expl ai n how

the categories go from the form, color, texture and move-

ment of external stimulations to the constitution of ob-

jectivity. His theory is based on the concept of neuronal

chart. A chart is a sheet of neurons whose points are sys-

tematically connected, on the one hand, at points on sheets

of receiving cells (skin, retina of the eye, etc…) to satisfy

entries of signals and, on the other hand, at points located

on other charts to satisfy reentries of signals functioning

in the two directions. His second idea was to admit that

the brain, genetically equipped at the birth with a su-

perabundance of neurons, develops thanks to the death of

a number of these neurons due to a process of darwinian

selection. Lastly, his third idea was that parallel reentries

of signals occur between the charts to ensure an adaptive

answer. It is the ongoing recursive dynamic interchange

of signals occurring in parallel between maps that con-

tinually interrelates these maps to each other in space and

time. Categorization, therefore, is ensured by the dyna-

mic network of a considerable number of entries and

reentries selected by a multitude of charts [26,121,122].

Although distributed on many surfaces of the brain, the

inputs, at the same time connected between them and

connected to charts of reentries, can thus react the ones

on the others in a mechanism of functional segregation

for finally giving a unified representation of the object.

In other words, categorization is a global “encartage”

which does not need a program a priori, a “homoncule”,

to produce it. For Edelman, this mechanism is a plausible

working hypothesis because his research group has shown

that brain-based devices are capable of perceptual cate-

gorization and conditioned behavior [123]. Over the last

14 years, a series of robotic organisms (called Darwin se-

ries) have indeed been used to study perception, operant

conditioning, episodic and spatial memory, and motor

control through the simulation of brain regions such as the

visual cortex, the dopaminergic reward system, the hip-

pocampus, and the cerebellum [124]. However, to reach

the major stage of conscious perceptive experience, Edel-

man thought that at least six further conditions shou ld be

met [26,122,125,126]. Firstly, the brain must have mem-

ory. Memory, according to Edelman, is an active process

of recategorization on the basis of a former categorizatio n .

The perceptible category, for example, is acquired by an

experience by means of charts of reentries. But if there is

a perceptive entry by seeing, for example, a table again,

one recategorizes this entry by improving preceding ca-

tegorization, and so on; one reinvents the category con-

tinuously. In other terms, memory generates “informa-

tion” by construction: it is creative but nonreplicative.

Secondly, the brain must have a system of training. The

training implies changes of behavior which rest on cate-

gorization controls by positive or negative values; an ani-

mal can choose, for example, what is clear or dark, hot or

co ld, etc, to satisfy i ts needs for surv ival. Thirdly, altho ug h

self-awareness appears only with the higher conscious-

ness, the brain must have a system of diffuse feelings

which enables it to discrimin ate between oneself and not

oneself. Fourthly, the brain must be able to categorize the

succession of events in time and to form concepts pre-

linguistics. Edelman thought that the categorization of

successive events and the formation of these concepts

have a common neurobiological substrate. Fifthly, there

must be continuous interaction s between cond itions 1, 2,

3 and 4 so that a particular memorial system for the val-

ue s is formed. Sixtly, the brain needs also to have reentrant

connections between this particular memorial system and

the anatomical systems. That is, according to Edelman,

to formulate a model of primary consciousness it is nec-

essary to have the notions of perceptual categorization,

concept formation, and value-category memory in hand.

As Changeux, Edelman considered that it is the tha-

lamo-cortical system, called “dynamic core”, which con-

tributes directly to the conscious experience [125,126]. It

is a dense fibre network inter-connected in the two direc-

tions, in which connections occur unceasingly and come

in competition so that the most effective fibres carry it

(according to a process of darwinian competition). This

reentrant dynamic core is thus a process, not a substance.

It is in perpetual rebuilding (with periods of time of a

few hundred milliseconds), in wide space but formed

nevertheless of unified and highly integrated elements.

As spatial process, it ensures the coherence of conscious-

nesses states ; it is the principal dynamic driving core of

the constitution of self. The key structures for the emer-

gence of consciousness are the specific thalamic nuclei,

modulated by the reticular nucleus in their reentrant con-

nectivity to cortex, the intralaminar nuclei of the thala-

mus, and the grand system of corticocortical fibers. What

emerges from these interactions is th e ability to cons truct

a scene. This activity is influ enced by animal’s history of

rewards and punishments accumulated during its past. It

is essential for constructing, within a time window of

fractions of seconds up to several seconds, the particular

memory of animals, that is the “remembered present”

[126]. Higherorder consciousness is consciousness to be

conscious, self-awareness. It is accompanied by a sense

of self and the ability to construct past and future scenes

in the waking state. It is the activity of the dynamic core

which converts th e signals received from the outside and

256 P. R. BLANQUET

inside of the body into oneself, what Edelman called “phe-

nomenal transformation” [125]. This higher conscious-

ness requires, at the minimum, a semantic capability and,

in its most developed form, a linguistic capability which

makes possible to symbolize the relations of the past,

present and future and to do representations. On the other

hand, Edelman asserted that the linkage proceeds from

the underlying neural activity to the conscious process

and not the reverse, but that consciousness is not directly

caused by the neural processes, it accompanies them.

Rather, they are the neural processes and the entire body

which are causal. Consciousness is “reincorporated” in

the body, insofar as it is one of the modulations by which

the body expresses its decisions; it amplifies the effects

of the body to produce th e free will [125]. Since the body

“is decided” by many nonlinear and chaotic determinisms

(described by Alain Berthoz [127]), consciousness is thus

also “decided” by these complex body determinations.

However, consciousness adds to the body an additional

level of complexity, because it is able to make differences

within a vast repertory of informations. What makes in-

deed informative a state of human consciousness is the

fact that the man is able to make a difference between

billion states different of things. The intentional under-

standing of consciousness to reduce uncertainty is always

singular and gives the character subjective and private to

mental-lived of each individual at every moment. Like

Dennett, Freeman and Damasio, Edelman thus admitted

that the free will is a nonlinear chaotic causality, gener-

ally circular, which results from the complex interactions

between the body and the brain in the local environmental

contexts. The model of Edelman offers an interesting ten-

tative of unifying the hard and easy problems. Indeed,

since the reentrant dynamic core theory considers con-

sciousness as an emergent property of any system shar-

ing specific core mechanisms of differentiated integra-

tion, the most reliable index of consciousness should

reflect the quantification of this core mechanism. How-

ever, a conceptual difficulty of this h ypothesis lies in the

paradox of trying to prove that neural indexes are more

respectable because they supposedly probe phenomenal

and not access consciousness. Indeed, neural indexes of

any sort have to be validated by confronting them at one

point with some kind of report, hence with access and

not phenomenal consciousness. Even if it turns out that

one of these neural indexes turns out to be perfectly cor-

related with consciousness, and thus becomes a perfectly

reliable measure of consciousness, then one might still

ask whether we have made any progress.

5. Conclusions

A great variety of specific theories have been proposed,

whether cognitive, phenomenal, physics, neural or based

on Artificial Intelligence, to explain consciousness as a

natural feature of the physical world. The most prominent

examples of philosophical and non-neural approaches

included the naturalistic dualism model of David Chal-

mers, the multiple draft cognitive model of Daniel Dennett,

the phenomenological theory of Franscisco Varela and

Humberto Maturana and the physics-based approaches of

Stuart Hameroff and Roger Penrose. The major neuro-

physiological theories included the emerging spatiotem-

poral patterns of Walter Freeman, the visual system-based

approaches of Viktor Lamme, Semir Zeki, David Milner

and Melvyn Goodale, the phenomenal/access conscious-

ness model of Ned Block, the synchronous cortico-thalamic

rhythms of Rodolfo Llinas, the synchronized firing corti-

cal oscillations of Francis Crick and Christof Koch, the

emotive somatosensory processes of Antonio Damasio,

the neuronal global workspace of Jean-Pierre Changeux

and Stanislas De haen e, an d the reentrant cortical loops of

Gerald Edelman and Giulio Tononi. It is foreseeable that

the range of these models will extend in the future. For

example, it is supposed now that consciousness associ-

ated with the dream would be a rebuilding at the time of

the waking, related to relaxations of specific neuromodu-

lators on very short intervals of time [128]. Such a hy-

pothesis might generate new models. On the other hand,

new perspectives of Artificial Intelligence hav e a ttempt to

check the hypothesis of the functioning of brain archi-

tecture and simulate consciousness using both the meth-

ods and laws of informational machines and the process-

ing capabilities of biological systems. For example, series

of brain-based robots have been tested over the last dec-

ade to study perception, operant conditioning, episodic

and spatial memory, and motor control. Moreover, a su-

percomputer program, called Human Brain Project, was

given for objective to attempt to reproduce an artificial

consciousness in the future.

One can be skeptic, like Paul Ricoeur, as for the pos-

sibility of obtaining a true theory which makes a complete

synthesis between a speech “neuro” and a “psychologica l”

speech. The body is this object which is both me and mien,

but there is no passage from one speech to another [120].

Any attempt to confuse the figures of the body-object and

body-lived of consciousness, was it founded on the prin-

ciples and methods of neuroscientific approaches more

innovating, is obviously impossible for ontologi cal reasons.

However, like Edelman says it, to deplore that one

cannot build a scientific model of consciousness without

being able to theoretically explain the quality of a quale

(what one feels, for example, by seeing the red of a flower)

is a non-problem; it is a problem of the same order as to

want to answer the famous philosophical question: “why

there is something and why not rather nothing?” [46].

257

P. R. BLANQUET

The subjective aspect of consciousness is a pure obvi-

ousness of the real world. It is a pure sensitive which is

given of only one blow of the medium of itself [129],

which it is impossible to analyze it without causing its

disappearance immediately. It does not remain about it

less than the neurobiological understanding of relation-

ships between the brain and the objective aspects of

consciousness is the great challenge which will animate

researches of future decades. Certainly, the phenomeno-

logical model of Varela is compatible with some experi-

mental neurobiological approaches. Likewise, the phys-

ics-based model of Hameroff and Penrose could be open

to some researches of mental-brain correlations via the

study of signaling mechanisms of synaptic functions.

Moreover, Artificial Intelligence has proven to be a fertile

physical enterprise to check some hypothesis about the

functioning of brain architecture, although no machine

has been capable of reproducing an artificial conscious-

ness. However, only the advances in neurosciences seems

actually capable of taking into account the constraints of

a wide range of complex properties to provide an ade-

quate explanatory basis for consciousness. Of these pro-

perties, several stand out as particular challenges to theo-

retical effort, in particular the property of intentionality,

the problem of explaining both the first-person and third-

person aspects of consciousness, and the question of plausi-

ble necessary preconditions to develop self-awareness. As

attests it analysis and the myriad of neurophysiological

data already available, the states (arousal) of conscioun-

ess, the behavior, the brain processes of conscious sys-

tems, and a number of subjective contents of conscious-

ness (some qualia) are objectivable and can be experi-

mentally studied. In spite of innumerable difficulties which

one will still meet to study and understand a phenome-

non which is the originating base of categorical repr esenta-

tions of the intersubjective and subjective world, it is

therefore possible that one will manage one day to build

a naturalistic satisfying explanation of consciousness that

links together molecular, neuronal, behavioral, psycholo-

gical and subjective data in an unified, coherent scientific

theory.

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