(a)

Global internal states of the organism.

The most important of these are:

(b)

Activity of special functional systems of the nervous system.

This is in particular the system for active functioning, the orthosympathic (the so-called effort system, Sympathetic-Nerve Activity, SNA), and more specifically and centrally the control system for vigilance, the Ascending Reticular Activating System (ARAS) in the formatio reticularis, a net-like system of nuclei and circuits in the brainstem (truncus cerebri). This activity is accompanied by, among other things, faster heart rate (heart rhythm), higher levels and greater variance of blood pressure, higher tone of skeletal muscles, and so on.

(c)

Activity of certain neuro-anatomic areas.

Consciousness seems to be located in specific neuronal areas. Traditionally, a very simple reasoning is followed to identify the brain areas which might be locations of consciousness.

This representation of affairs is, however, unsustainable with regard to the neuronal areas that may cause or maintain consciousness as a mode of functioning of the brain. Crucial to the emergence and the maintenance of conscious functioning remarkably appear not to be, as the myth would have it, the 'higher' brain areas, like cortex cerebri, that we associate with primates and humans, but most notably the evolutionary 'older' fish, amphibians and reptile brain.

A number of neuronal phenomena which usually coïncide with ordinary waking consciousness, appear to gradually increase shortly before the waking state, and only decrease again after loss of consciousness - in deep sleep, anaesthesia and so forth. In particular, these concern factors causing increased vigilance and global activation (arousal ) of the organism. With higher vigilance typically an increase takes place of the intensity of consciousness, as well as increase of alertness, extroversion, effort and action readiness, and motor mobility (dominance of the sympathetic system).
The overall level of vigilance thus forms an important neuronal correlate of consciousness. It is mainly arranged by the so-called Ascendent Reticular System, located in the central nervous system, in particular in a network-like structure of fibres and nodes called formatio reticularis. The formatio reticularis extends over the brain stem (truncus cerebri) - consisting of exstended marrow (medulla oblongata) and bridge ( pontis varolis) - the midbrain (mecencephalum) and the mediate brain (diencephalum, especially the thalamus).

An increasing arousal follows increasing activity of specific nerve nuclei in the brainstem (in the formatio reticularis) and the release of specific neurotransmitters (especially mono-amino acids and glutamate).
The waking state is related to activity of among others the following neuro-anatomical structures, that all produce neuro-transmitters that have a fast, activating effect (an excitatory nature).
All these structures and substances play a role in regulating vigilance, arousal and sleep-wake rhythm, and thus also with the emergence and maintenance of consciousness. Moreover they play a role during REM sleep and its episodes of mental activity and conscious dreaming.

(d)

Activity of specific neurotransmitters.

The aforementioned neurotransmitters play a rol as follows:

(e)

Activity of specific neuronal cell types.

In effect of the aforementioned subcortical processes and substances, functions in the more 'modern' areas of the cerebral cortex (cortex cerebri) are among others globally stimulated, activated and modulated.
After preliminary unconscious processing by "interneurons", principal neurons present in the cortex provide for decisions about sending of 'summarized' signals that may come under conscious attention (P.M. Churchland, 1993).
Those principal neurons particularly constitute of so-called pyramidal cells: relatively large, fast-acting neurons that fire their signals in powerful bursts (bursty pattern) with frequency upto 5 Hz. They work activating (excitatory) instead of inhibitory.
These pyramidal neurons mostly lay in the neocortext (and further in the hippocampus and the amygdala ), in particular in the deeper, so-called inner pyramidal layer (cortical layer V, the lamina ganglionary; cf. Crick, 1994, p.251). They seem to be mainly involved in higher sensory, motor and cognitive processing, memory tasks, and conscious intentional attention (Shepherd 1994, Crick 1994, p.251, Ransford 1995).

(f)

Post-synaptic (dendronal) receptors.

Important in this regard are post-synaptic receptors of the relatively quick, NMDA-activated type (NMDA = N-methyl D-asperate). These are found in the dendronal synapses of pyramid cells.
They are partially voltage-sensitive, and have a critical voltage threshold of -35 mV of the postsynaptic membrane potential to become activated by presynaptic release of fast neurotransmitters such as glutamate (H. Flohr, U. Glade, D. Motzko, 2000; in: J. Schulte am Esch, J. Scholz, P.H. Tonner (Eds.)).
In partical the NMDA receptors become disabled with general anaesthesia. Thus they turn out to be crucial for maintenance of subjective consciousness.

(g)

A dominant role of specific ions.

In the transition from unconscious to conscious processing specific ions may play a role. These are mainly Calcium, but probably also Sodium and Potassium. They are important in processes such as:
Especially ionized Calcium (Ca++) serves, among others in NMDA receptors, for transduction of an electric signal and its transposition into a chemical signal inside the cell, which can help to depolarization of the cell. (Cooper et al. 1991, Levitan & Kaczmarek 1997, p.124).

(h)

Specific Brain activity.

During conscious episodes, the active brain areas show, roughly said, specific signal patterns and brainwaves with typical characteristics. This is particularly the case during wakefulness but also, albeit much less unambiguous, at various sleep stages with dreamlike mental activity (mentation) that is subjectively noticeable as conscious sensations.
The general - and obvious - idea is that there is a symmetry between processes on distinct levels of functioning:
First of all it turns out that during conscious episodes a global 'undertone' of activation occurs, as well as local activity in connection with specific stimulation, focused attention, and intensive mental processing or effort.


(i)

Other potentially relevant neurophysiological phenomena.

All kinds of other neurological processes and functions are proposed to be characteristics, carriers or causers of consciousness, e.g. special micro-biological structures such as so-called ' microtubules', which are proteins who are located in certain neuro-synaptic gates and channel (cf. a.o. Stuart R. Hameroff & Roger Penrose, 1996).
It should be noted that all these theories are highly speculative, or even improbable in more ways than one (cf.a.o. R. Grush & P. Smith-Churchland ).

(1) The characteristics must be truly only present, and play an active role, in relation to the actual presence of subjective consciousness.
(2) It must also be proven that these characteristics cannot apply as well, to a greater or lesser extent, to unconscious, preconscious or unconscious phenomena.

(1)

Not necessarily unique.

It's difficult to determine to what extent all characteristics of cortical activity really are unique for consciousness, that is, never are present without consciousness.
A lot of those factors, variables and interactions turn out to be, and sometimes to a large extent, active during unconscious states. In that case it is excluded that they really are a sufficient indication for consciousness.
(2)

Not necessarily inherent.

In addition, it is difficult to determine whether features like high cortical activity really are inherent to conscious, that is, are always present when consciousness is present.
This showes that it is also impossible to designate specific neuronal characteristics which are strictly necessary for subjective consciousness in contrast with function unconsciously.

(a)

Degrees in consciousness and experience intensity.

The intensity of consciousness and experience is considerably correlated at the global level of neuronal activity. (We can find an analogy for this in physical measures of intensity, such as power, energy, and the like).

(b)

Degrees in conscious-to-unconscious transit phases.

Conscious states, episodes or phases have a gradual transition, boundary or demarcation in time as opposed to unconscious or less conscious phases, processes and contents. This is strongly related to the sleep-wake rhythm, and within the sleep cycle, with the most striking phase changes: (1) from waking to the first stages of sleep or non-REM stages, (2) from the last to the REM sleep stage with any conscious dreams, (3) and from there to (conscious) awakening. It appears somewhat harder to determine of psychological contents where precisely the boundary lies between conscious experience and unconscious processes, because this is highly individualized and instantaneous (the Introspection problem).
With respect to sleeping and waking stages we can find numerous characteristics and correlates in processes and structures of the nervous system. But to decide which one of these possibly delivers a robust causal contribution to consciousness, appears to be an extraordinarily complex problem.

(c)

Degrees in conscious-to-unconscious contents.

There is a gradual delimitation of conscious content as opposed to unconscious or less conscious content. The selection of mental contents for consciousness is somewhat indicated by the direction of conscious attention, and the activation of specific neuronal areas such as sensory and somato-sensitive function fields in the spinal cord, the extended marrow, the thalamus, and the cortex.

(d)

Indirect relation between modalitiesof subjective mental content and physical laws.

Consciousness always 'contains', as it were, some subjective experience content. For example sensory perceptions, physical and/or emotional feelings, memories, fantasies, reasoning, expectations, desires and dreams. These contents may in principle also remain unconscious, stronger, there are no indications of intentional content that were not before, at the same time or after unconscious.
In any case the conscious contents belong to subjective experiences, and the latter to the more general, psychological contents. We can establish that our conscious sensations not all come down to the same thing, they can have countless differential properties. We can look however for main lines, the dimensions or categories of mental content. Then first and foremost we'll find the sensory modalities and submodalities. These modalities we experience subjectively in qualities such as image, sound, feeling, taste and smell.
Of course we can trace back the sensory categories with the help of scientific knowledge (particularly physics) to certain characteristics and laws in the physical domain. For example, what we in general, subjectively and intersubjectively, perceive in the visual modality as the color 'red' appears to coincide with certain measured values of light waves i.e. electromagnetic radiation, in the visible spectrum, namely one wavelength of roughly 627 to 780 nanometers respectively 478 to 384 teraHz. It is clear however that we don't need that knowledge at all to experience the qualia of our mental contents, like the 'redness' of red. Moreover, although those physical laws may be well descriptive for the processes in external empiricism, they are not, and certainly not directly, relevant to our immediate subjective perception.

(e)

Indirect relationship between modalitiesof subjective psychic contents and neurophysical processes.

We can thus make a division, or mapping, of conscious contents to their corresponing neuronal-related dimensions, like sensory channels, i.e. sensory and somato-sensitive modalities, systems and circuits. These, in turn, are clearly correlated with specific neuroanatomical and physiological components in peripheral and central nervous system, such as sensory organs, neuronal cell types, fibers, tissues, and trajectories, synaptic receptors, transmitter molecules, ions, brain waves, locations, and functional areas of cerebral organs like thalamus and cerebral cortex, etcetera.
Therefore, all indicates that the substantive subjective experiential features - i.e. characteristics of conscious content - are constructed through neurophysical processes in the central areas of the cortex.
Ironically, however, it's precisely there, that we still can not find them at all through empirical observation.
The relationship between these neurophysic processes and consciousness thus has to be highly indirect concerning experiential content.

(f)

Indirect relationship between form aspects of subjective mental contents and physical characteristics.

The content of conscious perception has all sorts of other form aspects or quantitative aspects. Some subjective form aspects of consciousness have a strong resemblance to physical properties, and that counts first and foremost for the totality of our subjective experience at virtually any moment of daily conscious wake functioning. This totality is also known as the so-called ' Bubble of Perception' (D. Gordon, 1984), or the "Cartesian Theatre (a.o. Dennett & Kinsbourne, 1992b, pp.234-247).
The contents of this intra-psychic 'space-time' can be are related with external environmental observations as well as internal sensations (like memories, thoughts, feelings, etcetera).
Properties like these clearly bear a certain relationship of resemblance and correlation with dimensions of physical reality, but we can hardly persist that they "are" physical in the same way.

(g)

Network structure in conscious thinking and decision making.

The 'behaviour' of conscious processes such as thinking and deciding may well take place in accordance with the general system of signal processing in the nervous system, which resembles a network structure (neural network , neural net).
We can empirically recognize this network structure from the quick divergence and convergence of chemical and electrical signals, such as neurotransmitters and action potentials in the nervous system (to be made visible using scanning techniques such as EEG, MRI, PET, CAT, etc.). The point is, however, that these characteristics can also occur in unconscious psychic processes, including subliminal cognitive processing. So again it turns out that similarity, coïncidence or correlation of certain neuronal properties provides insufficient grounds to assume a causal or other derivation relationship with consciousness.

(a)

Gradual Difference.

Or difference 'of the first order' (Bateson, 1970). That is any 'significant' deviation of utter noise or random variance (signal-to-noise ratio), so it's a gradual difference, continuous and analog in nature. The detection of this type of difference depends on arbitrary sizes, scales and criteria for 'significance - and so it is not unequivocally determinable.
We can easily establish that the nervous system pre-eminently works with distinctions, and also that, as a general rule, during conscious episodes more striking patterns are detectable in brain activity.

(b)

Change: phenomena with process character.

This concerns in particular the ongoing variation in conscious processes. These may be related to the varying patterns of neuronal 'impulses' or 'signals'.

(c)

Statistically detectible coherence.

For example correlations between different neuronal processes.

(d)

Ranking of physical phenomena.

In particular arrangement of neuronal processes to space and time coordinates.

(a)

Unequivocal difference.

This kind of difference is called difference "of the second order" (G. Bateson, 1972).
It follows logically from distinctions and ordering patterns that have already been pre-accepted - some particular frame of reference, context or scenario, that has become 'fixed' - and it is discontinuously, discreet and digital in nature. The detection of this type of difference does not depend on arbitrary sizes, scales and criteria for 'significance' - and therefore it is unambiguously decideable.

(b)

Discrete information units.

This information consists of demarcated, discreet units, it exhibits as it were a "pigeonhole structure".

(c)

Syntactic coherence.

The ordering relationships within this type of information are typically 'syntactic' in nature. They have as such no inherent meaning of themselves, and are not bound to a certain specific or fixed interpretation.

(d)

Medium-independent.

Because of her syntactic nature this information is also not bound to a specific (physical) 'raw material', a carrier or medium. As a result, this information the property of Multiple Realizibility.

(e)

Not physically reducible.

This type of information is not reducible to physical domain. We may rightfully say that In this respect she is immaterial.

(f)

Sequential organization of information.

Because of the aforementioned properties this information can be encoded one-dimensionally. This implies for example the possibility of "linearization" (Chafe, 1970), that is applied by natural language ability in the construction of language structures.

(g)

Quantifiability.

The foregoing leads to the consequence that this type of information is countable and measurable: it is quantifiable . Two sub-forms count:

(h)

Availability for analytical information processing.

This information is basis of processes of "formal intelligence", which includes abilities like combining, reasoning and arithmetic. These include induction and modelling, logical analysis and deduction, causal explanation and prediction, verification and falsification, etcetera. This includes possibilities as feedback and recursivity.

(i)

Immunity for qualitative difference.

This kind of information is, on the other hand, inherently "qualitatively neutral", in other words, qualitatively irrelevant.
A process in which quality arises out of quantity a so-called "emergence", is very hard to imagine. This of course concerns in principle a reduction problem.
From a general materialist view, this process should be causal. And indeed, the concept of emergence suggests this, although somewhat vagely, if not mystifying.
However, causal processes are typical - if not unique - to the domain of physical phenomena. The domain of quality (information) only contains relations of logical combination and derivation. The domain of quality (subjective awareness), on the other hand, only contains relations of associative combination within the 'virtual' space-time of consciousness. Neither of the two domains concerned shows any sign of causal processes, or any laws, mechanisms or dynamics of causality for that matter.
Of course, we may suppose that at least a factor is required that directly delivers a qualitative contribution or component to some quantity. But this assumption only shifts the question to the precise workings of that factor, and the origin of that contribution, and the realization of its effect.
The conclusion must be that no trace can be found as yet of a solution to this reduction problem.

(a)

A subjective reference point.

An observational position, a reference point or point of view.

(b)

Recognizability.

That is, recognition of difference, distinction.

(c)

A a coherence (coherence) exists in subjective perception.

The interconnection of content (coherence) becomes apparant from aspects of continuity, wholeness and unity. This coherence gives structure to mental contents. That structure is needed for subjective matters, such as 'understanding', 'insight', 'knowledge' or 'knowing' and the like, with regard to situations or situations. Again applies that such mental contents and their structural characteristics can very well also be unconscious, more specifically in the form of state characteristics of neurophysiological substances, structures and processes. And of course the concept of coherence has no meaning whatsoever at the physical process level.

(d)

Referring function.

Coherence creates the possibility of subjective referral relationships, or meaning relationships between content data.

(e)

Functiuonal to meaning.

The relationships of meaning determine the extent to which actually can be referred to matters, so-called intensionality, or aboutness.

(f)

Consciousness relates to 'higher' intelligence.

Within consciousness, among other things, processes take place of information processing; via perception, cognition and rational thinking: like logical analysis, modeling, deduction, prediction or expectation, planning and behavioural control.
Consciousness is strongly related to memory tasks, such as learning processes and retrieving or re-activation of data and reaction patterns. Consciousness is in particular connedted to contents of the so-called Short Term Memory (STM), which can be compared to the dynamic or virtual 'internal memory'. of computers. Such content are exchanged with content from the unconscious Long Term Memory (LTM), which can be compared to 'fixed' memory bansk of computers like hard disks, CDs, DVDs, pen drives, etc.).

(g)

Consciousness mainly relates to the end result of psychological processes.

Consciousness is apparently a gathering point of 'summarizing' data from pre-conscious processing.

(h)

Conscious processes are concentrated and focused in conscious attention.

Conscious attention serves as a special focus, it acts as a kind of 'internal spotlight'.
Processes under conscious attention are characterized by sequential processing.
The 'concentration' in thinking depends on all kinds of variable characteristics of the attention: gradations in convergence, mobility (volubility), distribution, firmness (stability) and steerability.
(i)

Potential of self-reflexive cognition.

The conscious sensation process is in principle prone to a self-reflexive ability. As a result the possibilities arise of self-referential perception, cognition, valuation and evaluation. This is for example necessary for the formation of a self-concept or 'self-image' (Concept of Self , see below). However, these processes can of course also take place unconsciously.

Reference is hereby made to various types of modelling and information processing in human thought. We can think on several cognitive functions in this regard:

Here we see a series of steps in increasing subjectivity, abstraction and complexity. Thought is that consciousness would arise in particular out of the most advanced forms of mental representation.

(1)

Conscious introspection.

For example: conscious 'supervision' in the course of thinking, feeling and reacting.
(2)

Conscious awareness of conscious knowing.

The ability to consciously know or notice that one has a conscious awareness of something: a self-reflexive awareness of consciousness. After all, we can 'observe' directly within our consciousness what we ourselves - consciously - think and feel. And next we can realize that we're 'watching' this consciously.
(3)

Conscious self-awareness.

The conscious experience or noting that one is a "self". an individual, person, etc.., with their own, unique subjective perspective or point of reference. An "I-feeling", "Self-feeling", "Me-awareness, ( self-awareness).

(1) Conscious awareness of a range of available choices or options.
(2) Experience of a certain room for conscious choice.
(3) Formation of subjectively preferred value (appraisal, appreciation, evaluation, preference), determining the extent of (in)desirability.
(4) Formation of a conscious target outcome, objective, intent, motive (intensionality).
(5) Conscious concept formation, selection, eventually also planning, of a desired action or operation.
(6) Conscious decision, will, or "free choice".
(7) Actually operational conscious self-management (with feedback-guided modification).
(8) The conscious choice to recognize one's own freedom of choice: taking responsibility.
(9) Conscious meta-evaluation: a conscious retrospective evaluation with respect to one's own evaluations, and thus considerations, goals, choices, reactions and conduct.