Change of Paradigms in Consciousness Research

Dieser Text auf Deutsch.

Table of Contents

Change of Paradigms in Consciousness Research

On the Evolution of Consciousness

Even the simplest organisms, such as those consisting of but a single cell, interact with their environments. As metabolic systems in a balanced steady-state, all organisms must obtain nutrition from their surroundings. As they do not live in a vacuum, organisms are also in constant contact with the water or air around them, and they are also exposed to solar radiation and other electromagnetic and chemical influences. The long-term interaction between organisms and environmental stimuli resulted in development of various sensory systems for detecting the diverse external stimuli on which the organisms rely for food or which they must avoid as dangerous. In both cases, a sensory apparatus had to be developed which, via the interneurons , automatically provided signals to the motoric cells for inherent responses of flight or approach.

The Phylogenesis of Symbolic Information

It is necessary to recall these ancient interactions between organisms and their surroundings because they gave rise to the development of sensory systems appropriate for the physical stimuli. However, whereas environmental stimuli in the form of energy and food were ingested, the sensory apparatus evolved into organs which did not take in the stimulus itself, but rather received information about it. Only in plants do photoreceptors still serve as a source of energy. As the environment of multicellular organisms expanded, and stimuli to which organisms had to react in order to survive became more varied, the processes of trial-and-error and natural selection led to development of stimulus filters in the form of receptor systems which reacted only to combinations and sets of stimuli that were of importance to the organism. These combinations of stimuli relationships were embodied by a sensory apparatus capable of selecting stimuli according to certain categories, determined by biological factors. During development of sense qualities in the course of evolution, the formation of invariants played a key role, for recognition of food or predators under varied conditions of light and the surroundings was essential for survival. Therefore, it was advantageous to have a sensory apparatus capable of identifying stimuli by means of a filter consisting of signals generated by the apparatus itself. This mechanism, in turn, was capable of evolution.

Very early in the course of evolution, we encounter the colorful world of flowers, colors, sounds, shapes, and scents which grew out of the interactions between insects and their environments. The question as to whether bees respond only to certain electromagnetic wavelengths, that is, whether they react to physical stimuli or actually to certain colors, was resolved by von€Frisch, whose experiments showed that they really do respond to the same colors, even under changing conditions of light and wavelength.

To be sure, neither color nor light nor other sense qualities really exist in the environment: They are products of the sensory apparatus, which selects them by means of its filter. The sense qualities perceived by insects and other invertebrates are projected by the sensory filter onto the physical stimulus. Thus, the latter serves as vehicle carrying symbolic information to the sensory system. The sensory filter serves both as the projector and the receiver of sense qualities. The sensory apparatus uses its own analyzers to process the stimulus signals in such a way that it responds only to certain colors or sound sequences.

With these filters and analyzers, the sensory systems "invented" an entirely new form of information: Instead of physical properties that cannot be transferred to sensory channels, a representation of them was selected and produced, namely, the filtered sense qualities. Such a representation is also referred to as a "symbol"; therefore, one may refer to sense qualities as elements or signs of symbolic information.

As implied by the aforementioned insect's world of colors, sounds, and scents, the sensory filters of sense qualities not only filter, but also project sense qualities onto the environmental physical stimuli, which animals take up only through the "eyeglasses" of sensory qualities. In other words, insects take up their surroundings in a form they develop themselves. The symbolic information requires a material carrier. When a sense quality is projected onto a physical stimulus, the stimulus also becomes a carrier of sense qualities, so that in this guise they may be picked up and processed by the senses. Otherwise, it is difficult to conceive of how the colors, flowers, and scents in an insect's world might have originated.

The entire visual world is based on this type of projection: The eyes, instead of picking up electromagnetic waves which a physical object has absorbed and assimilated, receive only waves which are reflected or deflected without having penetrated the physical object. Therefore, it is not the object itself which meets the eye, but only a projection of the waves the object failed to absorb.

The sensory filter, too, functions in a way similar to that in which vision is affected by eyeglasses, through which the surroundings may be perceived as distorted or sharp, red or dark. The filter evolved by interaction with the environment and natural selection. Even though stimuli passing the sensory filter take on properties of the latter, the sense qualities still are not states of the organism whose sensory systems interact with the stimulus to produce them. At this level, the symbolic information contained in sense qualities is the product of two material systems or mechanisms, namely, the environmental stimulus and the sensory apparatus. The information achieves an existence separate from that of the filter only in that the filter projects it onto the physical stimulus, which then becomes a carrier of information to the sensory apparatus. The symbolic information exists solely in a material carrier, which thus becomes an indispensible component. If the series of material carriers in the recoding chain, to be described below, is interrupted, the information is lost.

This preconscious origin of symbolic information in the interaction of the sensory system with environmental stimuli, of which the symbolic elements or signs are the sense qualities, is also a critical factor in the development of consciousness and its "language". The highly developed mammalian brain with its cognitive apparatus or organs is capable of obtaining the information about the external surroundings needed for central control of behavior only in preexisting terms of the symbols of sense qualities. In other words, an organism does not have to reinvent symbolic information about physical properties of environmental stimuli from scratch. "Consciousness" becomes an unsolvable conundrum if its origin is attributed only to the neural network without regard to antecedent developments. The symbols of information, that is, the sense qualities, are not derived from the neural network, which communicates with nervous impulses and neuronal potentials and stores and encodes the information contained in patterns of neuronal excitation.

Neurons and neuronal patterns are not the information itself; rather, they merely convey information. Thus, symbolic information originates outside its carriers. The sources of information for the neuronal network are the sensory systems with their receptors. A neuronal network that is cut off from the sensory system is incapable of creating symbolic information in and of itself; even to obtain information about its own state of excitation, the nervous system requires a sensory apparatus. Without a sensory apparatus, the nervous system receives no symbolic information, either about events within itself or about outside stimuli. Actually, an organism is unaware of processes which transpire subconsciously and automatically. Many neuroscientists ignore this fact and attribute their expertise to the nervous system. Notwithstanding, the nervous system is unsurpassed as a storage unit and processor of signals it obtains from the sensory apparatus and as a carrier of information.

In invertebrates, the sensory apparatus is directly connected to effectors by way of interneurons. The sense qualities of signals elicited by stimuli are analyzed, then signals are transmitted directly to the motoric cells, which react to the signals with genetically determined patterns of motility.

Even invertebrates are capable of reinforcing the connections among heavily used pathways of excitation, and thus of learning, despite lack of cognition, within narrow limits. However, aside from genetically programmed sensory filter and analysis cells, invertebrates lack the ability to store newly acquired information, to be recalled for later use. The memory of invertebrates still consists of the variable strength of interneuronal synaptic connections.

The Development of Cortical Information Storage and the Neural Code

Organisms had to develop a cognitive apparatus in order to utilize information about the outer environment to adjust their activities, thus using learning processes to expand the less adaptable behavioral program established by the genes. A long period of development was necessary before organisms were able to store and analyze information in the cortical network and centralize their controls in the reticulo-thalamo-cortical system. Only the organisms equipped with such a system became capable of taking up symbolic information and storing it.

In the course of time and evolution, organisms developed a neural apparatus that enabled them not just to react to symbolic information, but to utilize the sense qualities as elements of an internal language. This internal language opened unlimited possibilities for new symbols designating objects and events, such as the human language.

This purpose was served by the neocortical network, among others, whose primary and secondary sensory areas represent the peripheral sensory receptory system in the cortex, and continue its functions of analysis and filtering in a more refined way. For example, the visual system in the occipital and temporal brain lobes comprises six different fields, V1 to V6, in which light differences, colors, orientation and movement as well as shape and contours of objects are analyzed separately in specialized fields and neuronal assemblies. This analysis of incoming signals from the receptor fields of sense organs is a continuation of the sensory system's filtering function, by means of which the manifold sense qualities are selected before the act of seeing can take place. This subconscious analysis of cortical sensory fields, unlike the organization of the invertebrate brain, is not directly connected to motoric functions or effectors. The neural representations or cortical sensory detectors are the neural carrier or code for the sense qualities, which must be decoded into the original symbolic information in order to be invested with semantic meaning.

The Preattentive Phase

Preconscious, preattentive analysis precedes the first storage of information and conscious perception; it has a latency period of about 60€ms. The signals are transmitted to the sensory fields of the cortex by way of the lemniscate tract of the spinal cord, crossing two synapses. This process has been most precisely studied for the visual system.

During the preattentive orientation phase, the organism (more precisely, its central control system) and the stimulus excite primary arousal of the activation system itself and and the sensory fields. The body and its senses become aligned with the stimulus via the sensomotoric aminergic and cholinergic paths of the reticular brain stem, which probably releases the neurotransmitters noradrenaline, dopamine, serotonin and acetylcholine into the extracellular cortical fields, raising the excitation level of certain areas in preparation for uptake and processing of sensory signals. Furthermore, by way of branches of the sensory tracts to the reticular system, the stimulus induces a higher state of excitation in select groups of neurons. In the cerebral cortex, this leads to so-called expectation potentials, which increase gradually until the level of activation of the sensory areas becomes high enough to receive and process sensory signals. With a latency period of 70 to 500€ms, this preattentive preactivation phase then proceeds with the components N€100 to P€300 of the endogenous or exogenous event-related potentials to a state of conscious attention. During the preattentive phase, the subconscious transformation of sensory cells to sensory detectors by the sensory signals sets in, and the sensory neuronal groups must be primed for this function. Only after such preparation can the sensory apparatus be aligned with the stimulus and turned to it centrifugally, so that perception may occur. Experts still disagree about the latency period that elapses between the stimulation and conscious perception; in contrast to the 60€ms mentioned above, Libet found a latency of 500€ms. In any case, it is certain that more time elapses between stimulus and conscious perception than the signal needs to travel from the periphery to the cortex, even if it must cross two or three synapses. The brain needs this time in order to transform the signals into detectors and align them centrifugally with the stimulus.

During the preconscious sensory impression of the preattentive phase of perception, the sensory stimulus triggers the formation of detectors in the cortex. In other words, a neuron or group of neurons is attuned by signals of the sensory system to a certain sense quality, for which the cell or cell group may then function as a detector. Since this detector function is stored both by facilitation and in a pattern of excitation, it may be referred to as a code for and carrier of sense qualities.

Preattentive orientation proceeds subconsciously at the level of the nervous system. Not until sensory perception is attained can attention focus upon information as an object with which it can operate; only when this level is reached does preattention make the transition to the conscious attention of a cognitive system.

The Reticulo-Thalamo-Cortical System (= Activation System)

The task of the sensory system, which includes the sensory fields of the cortex, in the preattentive phase is to analyze stimuli, so that the sensory system can filter the stimuli and align the filtered sense qualities with the stimulus. Preattentive orientation precedes conscious sensation; it is the focussing, concentration, or strengthening of the excitation or activation of a neuronal field with sensomotoric functions. This activation of attention proceeds from the activating system and the nonspecific excitation which turns sensomotoric fields on and off, and involves activated groups of neurons in its functional unit. The relationship between the activation system and attention is so close that they are referred to as the attention system. Some of its manifold, reciprocal pathways of excitation extend from the brain stem across the limbic system to the prefrontal cortex; another path runs from the reticular system of the brain stem across the intralaminary or nonspecific thalamic nuclei to the upper layers and to layer€VI of the cortical columns, which are joined by the lemniscate sensory tracts in layer€IV (Newman/Baars 1993).

Since the activation system has been mentioned several times, a brief introduction to this neuroanatomic innovation in vertebrates is necessary. As recently as 1949, G.€Moruzzi and H.€W.€Magoun discovered in the brain stem a structure apparently devoid of specific sensory or motoric function, which was the reason why it had been overlooked for so long. However, the role it plays is a crucial one. Gradually it became evident that this structure serves as a central activating system that both monitors and regulates the level of excitation of the entire organism. It is conjoined with the limbic system, and through it with the autonomic nervous system and the hypothalamus to form a functional unit extending to the nonspecific and intralaminary thalamic nuclei and communicating via two tracts with cortical structures, especially the limbic prefrontal brain. The activating system contains its own nonspecific excitation tracts, by way of which it monitors and regulates not only itself, but also sensory and motoric functions. Because of its preeminence and the control function it exerts, it is a sort of metasystem within the central nervous system.

The attention system is served by neurons in the parietal, temporal, and frontal cortex as well as in the region of the supplementary motoric areas in field€6; the best-known example is the frontal visual field. In the immediate vicinity of these sensory fields with attention functions are the sensory hand-arm field and the like, all of which serve to align the body and sensory systems to the stimulus. There are several visual fields (prefrontal, supplementary, and parietal fields); the same is true of the other sensory systems. There are also several hand-arm fields in the immediate vicinity of the visual fields. This proximity suggests a coupling of eye-hand-arm control by the activation system. The premotoric cells of the hand-arm field (the anterior part of field€6) discharge during intentional hand movements, such as conscious grasping and when the mouth is used for similar intentional movements. The neurons also fired even if the ipsilateral arm or the mouth was used, indicating that the neurons do not reflect muscular activity; as further evidence, when the muscles were used for motoric actions, the neurons remained silent. Stimulation of the arm-hand fields elicited coordinated, stereotypic movements of the contralateral arm. These fields of selective attention serve to align the body and senses toward the stimulus (G.€M.€Edelman et al. 1990). These and the observations described above support the notion that the activation system has a whole roster of secondary sensomotoric fields at its disposal for vision, hearing, etc., distributed all over the cortex, when exercising its function of sensomotoric attention and coordination. The process of sensory perception and awareness begins in such secondary fields, which are subordinated to the metasystem. By way of these cortical fields, which are connected to the superior colliculi and the reticular nuclei of the brain stem, muscles of the sensory receptors are aligned toward the stimulus and adjusted so as to be able to follow the moving stimulus. This has been studied in detail for visual processes (Ch.€J.€Bruce 1990). The next question is how visual processes become seeing, and how other senses elicit conscious awareness and perception.

The development of symbolic information was possible only in organisms with some degree of central concentration of drive and behavior in the reticulo-thalamo-cortical activating system to make them capable of activity.

The contention that the activating system truly participates in conscious sensory perception and recognition, memory, and imagination is supported by several uncontroversial findings:

  1. If the nonspecific impulses between the intralaminary thalamic nuclei and the cortical sensory fields are blocked, consciousness is lost; the same thing also happens when the reticular system of the brain stem and the nonspecific thalamic nuclei are completely interrupted.
  2. If the collaterals, i.e., the branches, of the sensory tract to the reticular nuclei of the mammalian brain stem is interrupted, the animal ceases to react to stimuli, although signals still reach the intact cortex, where they can be detected (D.€B.€Lindsay 1957).
  3. If the reticular system of the midbrain is severed, the decerebrated animals lose the capability of attentive, conscious, centrally regulated behavior (S.€Grillner 1990).
  4. The prerequisite for conscious behavior in humans is simultaneous activation of the cortical columns of the sensory fields, i.e., of the upper layers or of layer€VI by the nonspecific excitation of the activating system, and of layer€IV by specific sensory excitation. If any one of these tracts is interrupted, conscious perception ceases (J. Newman and B.€J.€Baars 1993).
Therefore, conscious behavior evidently results from the synchronous interaction of two systems, namely, the reticulo-thalamo-cortical activating system (also referred to as the metasystem) and the specific sensomotoric system.

Most neurophysiologists concerned with explaining consciousness now recognize the role of the reticular activation system in conscious processes of attention, sensory perception, and memory. However, instead of explaining how the neural network and its processes elicit conscious behavior, Edelman, Crick and many others offer masterly descriptions of the neural events that accompany conscious behavior. These descriptions are still within the confines of psychophysical parallelism, which lacks appropriate categories to which the role of the reticulo-thalamo-cortical activation system, for example, may be assigned within the more comprehensive system of the organism of the whole. Such descriptions and analyses remain at the level of the neuronal network and its processes, which run in parallel to conscious processes. In other words, it is not enough to verify with psychophysical parallelism the existence of synchronous interaction between nonspecific activation system and the specific sensory system during conscious behavior. It is essential to demonstrate the active regulatory and monitoring functions exercised by the reticulo-thalamo-cortical sensory fields on specific sensory apparatus, including the cortical sensory fields involved in conscious processes (e.g., feeling, perception, memory, etc.), in order to supercede the level of psychophysical parallelism, since these systemic properties overstep the limitations imposed by the properties of the neuronal network.

Without Interaction with the External Stimulus, the Neural Code Cannot Be Deciphered

Although the preattentive sensory impression that precedes conscious perception and serves in formation of cortical sensory detectors and neuronal carriers of information by analyzing input signals in the various sensory fields has frequently been studied, documented, and proven by neuropsychologists and neurophysiolgists, the significance of this event has largely escaped attention. Nevertheless, the explanatory model for perception presented here stipulates preattentive analysis of stimuli before the activating system is able to align the sensory system with its appropriately attuned filters centrifugally toward the stimulus, from which it may decode the sense qualities. Many reputable researchers believe that the sensory fields of the cortex not only represent the indispensable analyzers of the stimulus signals, but go beyond that to actually generate sense qualities, for example, the categories of color in the visual system. In support of this notion, they refer to the observation that malfunction of the sensory fields causes the corresponding sense qualities to disappear. This observation, of course, is unquestioned, but the interpretation is subject to doubt; for although the cortical analyzer may be an indispensable prerequisite for sensory perception, it is not the only one. The sensory system, with its cortical sensory detectors attuned to the stimulus, still must be aligned with the physical stimulus in order to decode the sense qualities. Sensory qualities are generated and perceived by the system as a whole only when the physical stimulus meets the detector and information carrier attuned to it in a feedback excitation circuit.

In contrast, S.€Zeki, among others, attribute to the sensory fields of the cortex the ability to generate various sense qualities such as light, color, tonality, and scent ("transforming the signals reaching it to generate constructs that are the property of the brain, not of the world outside, and thus in a sense labeling the unlabeled features of the world in its own code"). Naturally, this would be the simplest explanation; but it is refuted by the fact that people born blind or deaf cannot be made to see or hear by electrical stimulation of their intact sensory fields. In other words, it is not enough for stimulus signals to simply arrive at the sensory fields of the brain, be analyzed there, and be transformed into detectors of selected sense qualities by the cortical filters. In addition, the sensory detectors and neural carriers of informaiton thus produced must be confronted with the stimulus, which must be present if the sensory system with its adjusted filters is to extract the sense qualities from the physical stimulus. This applies, of course, only to the elementary, nonspatial sense qualities.

When the sensory system and the reticular activation system report a stimulus and simultaneously activate the corresponding cortical sensory detector, the activation system directs aligns the cortical detector and its sensory system toward the stimulus. Corticofugal influences modulating the afferent impulses from the periphery have been reported in a number of publications (G.€D. Dawson 1958; K.€E. Hagbarth and D.€J.€B. Kerr 1954; G.€E. Mangun and S.€A. Hillyard 1990, pp.€271€ff.). This control center of centrifugal excitation involves the following events: The sensory system permits the stimulus to appear only through its filter, that is, the sensory system understands only its own projection of the stimulus, namely, the sense qualities it generates itself. However, these are not arbitrary products of the brain, as some presume. The symbolic information, that is, the sense qualities, can be generated by the sensory system only if the the physical stimulus is actually present to interact with it. Symbols invented by the brain would be self-contradictory, for they would represent no other physical reality. As already mentioned, electrical stimulation of cortical sensory cells fails to elicit perception of the respective sense qualities in persons born blind or deaf, even if their cortical sensory fields are intact. However, if the organism has already had such sensory experience, e.g., once seen colors or heard sounds, these experiences can be elicited again by electrical stimulation of the cortical storage, as experiments by Penfield, Libet, and others have shown. The initial sensory experience must therefore be gathered in the confrontation and interaction of the sensory system with stimuli from the outside world. This also applies to the so-called internal stimuli of the limbic system, which must first make a detour through interoceptive tracts of the peripheral or autonomic nervous system before they can be felt and perceived as sense qualities by the cortical detectors.

In addition to this evidence, several other observations also contradict the view that stimulus signals are transformed into sense qualities by the brain alone. Finnish researchers found the primary visual field of the cortex in blind people to be utilized by the sense of hearing. "In the deaf, the areas of the temporal lobe in which sounds are normally processed are used instead for processing visual information" (R.€Ornstein, R.€F.€Thompson). In Paris, Michel Imbert and Chr. Matin of Pierre et Marie Curie University interrupted the neural tracts connecting the thalamus (lateral geniculate body) and the visual cortex in a newborn hamster, since in these mammals the brain development is not yet complete at birth. The visual nerves were then attached to the somatosensory tracts, which had been likewise been cut, so that visual signals were sent to the somatosensory fields of the parietal cortex. After the animal recovered, the researchers were able to derive visual signals from the parietal field; the visual behavior of the hamster did not differ from that of normal animals.

These experiments clearly indicate that light, color, sound, and other sense qualities cannot be generated solely by the sensory fields of the cortex. The properties of analysis and filtering in the cortical fields are developed by interaction with peripheral sensory receptors by way of connections between the receptor fields and the cortical representations. Actual deployment of the filter function of the sensory system is possible only with an external stimulus, and the filter can switch to a generator of sense qualities only by interacting with this complementary part.

The Mechanisms of Generating Information

The symbolic information is generated by the interaction of two material systems, namely, the physical stimulus and the sensory system. In the course of evolution, they have become assimilated and adapted to each other and developed two complementary systems: both the physical properties of stimulation that must enter the receptor system and the filters of the sensory systems are adjusted to each other. The sense qualities emerge as products of the interaction between the physical stimulus and the sensory system. When sense qualities are projected onto the physical stimulus, the latter becomes their carrier, for symbolic information needs a material carrier. The sensory system reads or scans the carrier in order to obtain symbolic information generated within itself.

In mammals, the preconscious generation and transmission of information has been transmuted in that the sensory system is now part of an organism capable of self-regulating behavior. After preconscious adjustment to the stimulus, the central neural governor once again confronts the sensory system with the stimulus, but this time as an organ of attention under the control of the organism's central regulatory system, i.e., the activating system.

The condition of the sense qualities in the carrier of the physical stimulus is also the only decoded condition of the sense qualities to which the brain, by way of the senses it controls, has direct access to sensation and perception. Without these sensory events, the brain fails to perceive any decoded sense qualities, and without perception of sense qualities there can be no psychological or mental world; that is, there is no differentiation between subject and object until sense qualities are perceived. The self-generated conditions of the sense qualities are hidden from the brain or kept at an unconscious level until they confront the sensory system in a physical information carrier as an external object, rendering them accessible. This is made possible, as it were, by a trick of evolution, which has unlimited inventiveness: The same sensory filters that permit the sensory system both to project sense qualities onto the physical stimulus and to utilize the stimulus as its carrier of information also read and perceive the self-generated sense qualities from it, because they fit it like lock and key.

The sensory receptors and the sensory filters are not the only ones having a lock-and-key mechanism consisting of their self-generated sense qualities projected onto the physical stimulus; the cortical sensory detectors, too, are attuned to the sense qualities projected onto the physical stimulus as a key to a lock. The cortical detectors and the sensory filters are complementary systems, and form a functional unit themselves. For the transmission of symbolic information from the outside into the brain, evolutionary processes have led to a chain of complementary systems, along which symbolic information is transmitted and recoded from one level to the next higher one, without ever losing the material carrier, even temporarily. Sensory receptors and cortical sensory detectors are examples of such complementary systems, across which the same symbolic information in the decoded state is transmitted from the physical carrier to its neural code in the cortex. Since the complementarity or tuning between the peripheral receptor and the cortical detector systems is determined during embryonic development and in the subsequent period of learning, the simplest neural frequency code of all is sufficient: on or off, excited or inhibited. If complementary systems are activated, they are tuned in to each other, related to each other, or self-referent.

In principle, sensation is decoded when the central neural metasystem utilizes the nonspecific activation to align the sensory detector and the sensory system to the stimulus. Upon meeting it, the detector "recognizes" the physical information carrier by means of the tuned-in sense qualities, because they fit together. The long-established lock-and-key mechanism lives on in a more advanced form in this process of recognition, which is reminiscent of recognition of a receptor by a ligand. The information is transmitted by its original carrier, the physical stimulus, to the neural carrier, the detector, by way of an activity circuit with manifold feedback between the peripheral sensory receptors and the cortical sensory detectors.

The stimulus instigates a periodic process. "An optical or acoustical stimulus leads to periodic discharges in the addressed nerve cells", wrote E.€Pðppel. These discharges occur at intervals of about 30€ms, as shown by electroencephalography. Their periodicity enables the cortical structures to analyze the incoming signals, while once again aligning the sensory organ (e.g., the eye) to the physical stimulus, all at the same time. The centripetal and centrifugal excitation of sensation forms the feedback loop, already referred to several times, between the peripheral and cortical systems, and establishes synchronous peripheral decoding and its cortical representations.

There is a way to obtain scientific evidence that the neural processes under study actually do involve transmission and processing of sense qualities. It is based not on introspective experiences, but rather on verifiable data, in a sense, meta-data. To mention a few:

These and other data give us some knowledge of events of sensation, attention, and other conscious processes. At the same time, they permit us to draw inferences about processes which we cannot observe directly, but which are prerequisites for observable processes. Data of this nature are provided by experimental cognitive psychology.

Evolution developed the solution to a problem that network theoreticians have been working on without success to date. However, the point of departure for evolution was not a mechanical network, but rather an organism with a central activation system. One must find the activity of an organism capable of self-regulating behavior behind the feedback excitation loops of sensation in order to understand what actually transpires with these feedback signals of the nervous system. The origin of symbolic information in the interaction between physical stimulus and sensory system as well as the developmental stages leading to perception of these sense qualities by the attention of a mammal can be traced step by step (Hernegger 1995).

Decoding the Neural Code in Sensation

The neural network is a highly organized, complex system of nerve cells that can be broken down all the way to the level of its molecular components for study. The nerve cells have no "inner life", either individually nor as a group; they are capable neither of sensation nor of feeling. First, the activating system must align and prepare the sensory system and the cortical sensory detectors with the environmental stimulus before they can receive and process the sense qualities. Under the guidance and control by the activation system, the sensory apparatus, including the cortical sensory fields, is transformed to its organ of cognition. The transformation is initiated by the prior cortical analysis of signals from the peripheral receptor and the concomitant formation of a cortical sensory detector; the organ of recognition of the activation system can perceive external stimuli through its complementary filter only in the form of sense qualities, for the filter is now also the receptor of the sense qualities it generates itself.

But how does a perceived sense quality become an object of attention of the activation system?

Here, too, the importance and irreplaceability of the cortical sensory detectors is evident, even if it were only because of preattentive sensory impression represented by the neural code, which is later decoded by way of an excitatory feedback circuit with the perceived sense qualities. In this way, the neural carriers of information in the cortex are given the semantic meanings for the organism's central controlling system, which can now direct its attention, that is, its nonspecific excitation, to the cortical sensory representations or include and incorporate the excitation patterns of the decoded sense qualities into its own system. The activation system is actually capable of including neural structures in its functional unit and releasing them again. The inclusion of the sensory apparatus in such a functional unit transforms the sensory apparatus into an organ of perception of the activation system, the representation of the organism as a whole.

Before sensation occurs, the unconscious, preattentive sensory impression involves formation of a cortical representation or sensory detector of sense qualities in the neural code of the nervous system. This code must be decoded for the information to become an object of attention.

Once they have been tuned in to the stimulus, the sensory systems, regulated by the central system of attention, are aimed outward at the stimulus, in order to decode the neural representations or the neural code of the cortex by sensation or perception of sense qualities upon meeting the stimulus. Decoding means transforming one code into another one, or into a "language" which the recipient can "understand".

The recipient capable of "understanding" the language of sense qualities is not the isolated nervous system, in whose code the information is already stored, but rather the whole organism. Initially, although the sensory systems were directed toward the external environment, the organism was unable to sense, perceive, nor recognize anything, for lack of corresponding internal conditions, but was only capable of picking up symbolic information from outside of the central nervous system. For this purpose, it became necessary to transform the sensory system and the sensory cortex into an organ of recognition.

Decoding occurs via the feedback excitation circuit between the sensory receptor and the cortical detector. While the stimulus signals are sent inside to the brain, the brain directs the eye or ear (the sensory receptors) to the outside. By way of the reticular excitation pathways, however, the limbic-autonomic and the peripheral nervous systems, i.e., the entire organism, is involved in this process of sensation, perception and recognition, especially since somatosensory perception is involved in every other sensation. In sensory perception, feedback occurs between the organism and the nervous system by way of these complicated loops, and not only within the neural network, as contended by Edelman and most neuroscientists who are trying to find an explanation for consciousness. For this reason, the conditions with which the organism responds to sensory perception involve not only the nervous system, but the organism in its entirety. The two spheres are integrated by the feedback loops, however. Thus the organism is the receiver, for which the neural code must be decoded.

Sensation is reported to the corresponding cortical sensory fields via two separate pathways. The sensory signals reach the brain by way of a tract from the spinal cord. In the brain stem, collaterals branch off to various reticular nuclei of the activation system. The specific sensory tracts proceed further across specific relaying nuclei in the thalamus to the sensory fields of the cortex, but the nonspecific excitation in the reticular system of the brain stem divides into several paths. One such path leads to the part of the forebrain known as the limbic cortex, and another runs parallel to it through the nonspecific intralaminary thalamic nuclei to the same columns of the cortical sensory fields as the specific tracts, but in the upper layers (usually I and II) or in layer€VI of the columns, whereas the specific tract has as its goal cells in layer€IV of the same column. Feedback loops between the periphery and the cortex and between specific and nonspecific excitations synchronize these events.

The feedback excitation circuit of sensation or sensory perception occurs as long and as often as necessary until a firm linkage between the peripheral picking-up of sense qualities and their cortical representations has been developed. It is now known that short-term memory enters a long-term linkage by way of the hippocampal system. However, this association must be continually renewed, either by the same sensory experience or by dreaming (the REM phase of sleep). Complete sensory deprivation causes the brain to create hallucinations, during which, as in dreams, stored patterns are endogenously activated in the absence of a corresponding external stimulus.

The nonspecific neural patterns of long-term memory, which are complementary to the specific patterns, store the attention conditions of the activation system with which the organism perceived the decoding of the sense qualities. These conditions must be renewed again and again by practice and linked to the neural code.

With every new experience there is a tendency to disassociate the sense qualities from the environmental stimulus, to make it an autonomous, operant "coin" for the central controlling system. Parallel to this disassociation from the external stimulus, a linkage develops between the decoded sense qualities and their neural code or representations. Every sensation is a transfer of the symbolic information from the outside or from the periphery to neural representations by way of a pattern of connections, which finally form cortical excitation patterns.

Transformation of the Code of Symbolic Information

Before organisms equipped with sensory systems appeared, the lock-and-key mechanism was the code enabling information to be passed on. In the genes, in the immune system, and in transmission across synapses, this lock-and-key mechanism between ligand and receptor molecule is still to be found.

With the advent of sensory systems in organisms, a completely new kind of information coding cropped up, namely, symbolic information defined from the outset. The transition from an information filter to self-generated, detached information in the form of sense qualities was a fairly complicated process, especially since sense qualities cannot exist without a material carrier. First, for the neural network, the symbolic information contained in the sense qualities was translated into the neural code of nerve impulses and stored as a pattern of excitation of neuron groups. Then the central activating or attention system of the organism had to retranslate the neural code into sensory perception and associate the sense qualities decoded in this way with their cortical representations or carriers.

In the transformation of sense qualities to an object of an activating or attention system, somatosensory perception plays a critical part; it either precedes all sensation and perception, or transpires parallel to it. The body of the organism itself is represented severalfold in the parietal cortex (in areas 1, 2, 3, 5, and€7), and receives stimulus signals from the entire body surface, as well as from joints and muscles, by way of somatosensory senses; these exteroceptive somatic senses are supplemented by the interoceptive senses from the peripheral and autonomic nervous systems. This somatic sense, which is coupled by feedback with the motoric and activation systems, is crucial to the development of consciousness, for the self-reference of the periphery and the cortical equivalents by way of feedback between somatomotoric and somatosensory systems is the framework of all other sensations andperceptions. In other words, once this storing of experience of the body itself begins in the fashion described, it is continually renewed and elaborated. These somatosensory qualities derived from one's own body become the first "language elements" of the brain. They are simultaneously a state of the body and an object of attention, i.e., the somatosensory qualities are experiences of bodily conditions. The states of the body itself were able to become the object of attention only by being perceived in the way we know as symbolic information about the physical properties of stimuli impinging on the body. These somatosensory sensations are unique, because they can take place even without involvement of other sensations; the condition of one's own body can be perceived only as symbolic information. In other words, only symbolic information contained in somatosensory qualities can be an object of attention and perceived; somatosensoryqualities represent physical and energetic events within the body. In this fashion, an infinite series or infinite regression of conditions is prevented. The initial sensory perception cannot draw upon another condition, sensation, or feeling; it is actually the initiation of a process from which and in which conscious perception originates and happens. The organism perceives its own condition by way of symbolic information of somatosensory qualities as an object of its own attention.

Each sensation and perception can happen only by way of symbolic information of sense qualities, for there is no other way to become an object of attention or sensory cognition. It is naive and unreflected to attribute to the nervous system the ability to directly experience its processes and conditions. Only symbolic information can become an object of attention at which the sensory or cognitive systems are aimed. The only properties of physical events or objects which can be perceived are those which can be transformed into sense qualities. Consciousness and cognition have their wellsprings in this object formation.

Somatosensory perception proceeds along reciprocal pathways of the nonspecific mediodorsal thalamic nucleus to the somatic fields of the parietal cortex, among others. The somatosensory perceptions are connected in a special way, directly and inseparably, with the excitation of the activating system. Self-referring somatosensory decoding is the prerequisite for any subjective experience and the states it entails, for in this case the roles of sense qualities as objects and as states coincide in the decoded sense quality; with somatosensory perception, the organism also has an object of its attention, but the object is a condition of its own body. For this reason, in this context we speak of self-reference. The dual nature of decoded sense qualities as an object and as a state of the attention system may be explained by assuming that the activating system regards the decoded sense qualities as an object of attention, and incorporates it into its own system by way of nonspecific excitation; alternatively, the activation system may extends to include the cortical structures serving as sensory representations. The basis for this contention is the already mentioned fact that sensory qualities do not reach a conscious level until the excitation of the specific sensory systems and the nonspecific activation system unite to produce a state of common, synchronous excitation.

The perception of sense qualities happens via the previously described excitation loops in various patterns of excitation in the sensory fields and the prefrontal, parietal, and temporal, as well as the subcortical, reticular, and limbic-autonomic components of the activating system. The organism, which articulates itself in these patterns of excitation, is both carrier and object of the perception; its activating system is its organ by means of which the cortical structures of attention are steered toward the decoding process or to reactivate stored representations.

The organism, which distributes its nonspecific excitation to various cortical regulatory structures, is therefore what senses, perceives and feels. If the excitation of the activation system is turned off, the organism ceases to perceive anything. In this way, the organism, or its activating system, is in a state influenced by the process of sensation; this state is not consciously perceived as such, for only its products and the object it is attuned to, i.e., the perceived sense qualities, reach the level of consciousness. However, those sense qualities include somatosensory and interoceptory perceptions, including bodily states and the autonomic nervous system. The reference to this state of the organism, which is the foundation of conscious perception, is important for understanding the reactivation of memory; for it has been postulated that the program for reawakening of consciousness is coded in the nonspecific stores. The same condition enables the organism to perceive the decoded sense qualities as the object of its attention.

Before consciousness came into being, there were neither sensations nor feelings, perceptions of sense qualities, nor imagination. Nor was the brain able to generate these psychic events all by itself, so its only option was to take up information from the outside or from the environment and convert it to self-generated sense qualities. The road to conscious perception and cognition led from the filter of the sensory systems through the neural code of the brain to its decoding, based on the interaction of several complementary systems. The nonspatial sense qualities themselves are the elements out of which spatial forms, movements, and orientation of the body are constructed. The information symbol of the nonspatial properties bears no resemblance to the information carrier or the code, which is often a carrier of information as well. However, the brain's code for space and time properties retains a spatio-temporal similarity, a quasi-isomorphism with the spatial stimulus properties. Several nerve structures in the peripheral receptor, in the thalamus, and in the sensory fields of the cortex serve to analyze it. And these spatial secondary sense qualities are the elements for objects, classes of objects, and entire categories.

With this inexhaustible reservoir of symbolic information, the human brain was now able to creatively construct new mental worlds. The potential combinations possibilities of the elements of symbolic information, i.e., the sense qualities, are just as inexhaustible as the sounds of human speech. As a matter of fact, sense qualities and human language share the same line of development.

Let me recapitulate the critical stages in development toward consciousness:

  1. The origin of the development was the sensory system with filters for sense qualities, the elements of symbolic information.
  2. The sensory system changed with the development of the cortical network and the central driving or activation system, and became a centrally regulated organ.
  3. Every new perception is preceded by a preattentive sensory impression for unconscious analysis of the stimulus signals, resulting in formation of a sensory detector before perception. In the second, conscious phase of sensory perception, the sensory system can therefore be aimed outward and selectively, its filters already tuned in, toward the environmental stimulus. The filters match the sense qualities as a key matches its lock or a template its matrix. The sense qualities gathered in this way are the decoding of the neural code in the cortex. The peripheral process is connected to the sensory target neurons in the cortex by way of a feedback excitation circuit, forming a unit. The long-term connection between the neural code and its decoded sense qualities is established by learning.
  4. The symbolic information, or sense qualities, thus become an object of central attention. This object formation is the origin of cognition and consciousness.
The mere description of the neurophysiological substrate of sensation and perception, however comprehensive and detailed, can do no more than relate the observable events that accompany the process of conscious perception. The widely-held notion of psychophysical parallelism is satisfied to describe the correlation or parallelism between physical (i.e., neurophysiological) and psychic (i.e., conscious, phenomenal) events, without offering an explanation of how conscious behavior came into being from these neurobiological prerequisites. The neobehaviorists tend to consider the description of the physical, neurobiological events sufficient to explain them. In order to understand what goes on in neurophysiological processes, it was necessary to regard them in a more comprehensive framework of relationships and interactions, in which the central nervous system wass not treated as if it were an isolated, autonomic entity, separate and isolated from the organism.

We have replaced psychophysical parallelism, which for a century has amassed an incalculably rich collection of observations and data, by a different model that attempts to explain the interaction of various components not reducible to each other, i.e., symbolic information and the nervous system. In our model, the observations of psychophysical parallelism have a new importance and another interpretation; the temporal correlations of inseparable events are now regarded as interactions and interdependencies of systems that generate new products and new systemic properties. The process of sensory perception can be described separately from the standpoints of sensory physiology and perception psychology, and both descriptions are correct. Nevertheless, the same sensory perception can be described, as here, under the assumption that the other two are an information process in a dynamic cybernetic system. All three descriptions are justified, but they answer different questions.

The description presented here does not merely draw upon results of neurophysiological and psychological research; it also integrates them by studying system levels within the organism and how they relate to one another. E.€Pðppel formulated this systemic approach as a question: "How do individual system levels in biological systems come into being? How does something higher develop from a lower level?"

Conscious behavior has many facets, and can be defined in quite various ways. On the one hand, it is not an independent being hovering outside the body and transcending the nervous system. On the other hand, in contradiction to the so-called identity theory, it cannot be identical with the nervous system, for the first thing to become conscious is symbolic information about the external world, impinging from the outside and not generated by the nervous system alone.

The process of conscious behavior thus always involves two irreducible elements: a)€the recognizing organism, and b)€the recognized information, in which, in turn, information about the physical properties of the external stimulus must be differentiated from the self-generated symbol (i.e., the sense quality), by means of which the information is received by the sensory system. The symbolic information therefore goes beyond the neural process and is not reducible to it. The sensory apparatus and the sensomotoric cortex develop increasingly into organs of transmission, analysis, processing, and storage of this symbolic information, which it translates from one code into another during transmission from the peripheral sensory receptor to the cortical network, where finally the cortical representations are decoded into the original language. The symbolic information is what remains; it must not be confused or identified with the nervous system that transmits, processes and encodes it.

The sense qualities have not ceased to fascinate modern thinkers since John Locke (1632±1704). Immanuel Kant (1724±1804) regarded them as subjective forms in which we see things, and which rather tend to interfere with seeing "the things themselves". In that era, the notion of information was hardly important, but Shannon's concept of information turned out to be unsuitable in all attempts to apply it to consciousness. It was another train of thought in modern times, embodied by E.€Cassirer's "philosophy of symbolic forms", Karl Böhler's "theory of speech", or Susanne K. Langer's "symbol in thought, rites, and art", to name but a few, that paved the way for the notion of symbolic information. This notion probably had little or no influence on Shannon and Weaver as they developed their theory of information. Regarding sense qualities as elements of symbolic information about the physical properties of environmental stimuli opens entirely new perspectives and possible explanations for consciousness research. In this sense, consciousness research is part of the basic science of language theory, linking the origin of human language to phylogenetic development. Conversely, consciousness research profits from the methods and categories of language research, as long as the common fallacy of coupling consciousness with the origin of human speech is avoided, i.e., confusing cause and effect. It is not inconceivable that Shannon's concept of information and the development of mathematical formalism in theory of information that followed may also be applicable to symbolic information, permitting it to be quantified. Notwithstanding, such quantifying of information should not be confused with a mathematical model explaining consciousness; we are still far away from that.


  1. Bruce, C.€J.: Integration of sensory and motor signals in primate frontal eye fields. In: G.€M. Edelman et al. (eds.) 1990, pp.€261±313.
  2. Buser, P. A., E.€Rougel-Buser (eds.): Cerebral Correlates of Conscious Experience. North Holland Publ., Amsterdam 1978.
  3. Dawson, G.€D.: The central control of sensory inflow. Proc. Roy. Soc. Med., London 51 (5), 531±535 (1958).
  4. Edelman, G. M., W.€Einar Gall, W.€M. Cowan (eds.): Signal and Sense. Local and Global Order in Perceptual Maps. Wiley, New York 1990.
  5. Grillner, S.: Neurobiology of vertebrate motor behavior. From flexion reflexes and locomotion to manipulative movements. In: G.€M. Edelman et al. (eds.) 1990, pp.€187±208.
  6. Hagbarth, K.€E., D.€J.€B. Kerr: Central influences on spinal afferent conduction. J.€Neurophysiol. 17 (3), 295±297 (1954).
  7. Hassler, R.: Interaction of reticular activating system for vigilance and the corticothalamic and pallidal systems for directing awareness and attention under striatal control. In: Buser et al. (eds.) 1978.
  8. Hernegger, R.: Wahrnehmung und Bewuûtsein. Ein Diskussionsbeitrag zu den Neurowissenschaften. Spektrum Akademischer Verlag, Berlin±Heidelberg±Oxford 1995.
  9. Hobson, J.€A., M.€Steriade: Neuronal basis of behavioral state control. In: Mountcastle, V.€B., F.€E. Bloom (eds.): Handbook of Physiology. The Nervous System, Vol.€IV, pp.€701±825. American Physiological Society, Bethesda 1986.
  10. LeDoux, J.€E.: Emotional networks in the brain. In: Lewis,€M., J.€M. Haviland (eds.): Handbook of Emotions. Guildford Press, New York 1993.
  11. Lindsley, D.€B.: Psychophysiology and motivation. In: Jones,€M.€R. (ed.): Nebraska Symposium on Motivation, Vol.€5. University of Nebraska Press, Lincoln 1957.
  12. Mangun, G.€E., S.€A. Hillyard, in: Scheibel, A.€B., A.€F. Wechsler (eds.): Neurobiology of Higher Cognitive Function. Guildford Press, New York 1990.
  13. Meric,€C., L.€Collet: Attention and otoacoustic emissions. Neuroscience and Behavioral Reviews 18 (2), 215±222 (1994).
  14. Newman, J., B.€J. Baars: A neural attentional model for access to consciousness: a global workspace perspective. Conceptions in Neuroscience 4 (2) 255±290 (1993).
  15. Ornstein, R., R.€F. Thompson: The Amazing Brain. Boston 1984.
  16. Pðppel, E., A.€L. Edinghaus: Geheimnisvoller Kosmos Gehirn. Mönchen 1994.
  17. Scheibel, A.€B.: The brain stem reticular core and sensory function. In: Handbook of Physiology. The Nervous System, Vol.€III,1. American Physiological Society, Bethesda 1984.
  18. Scheibel, A.€B., A.€F. Wechsler (eds.): Neurobiology of Higher Cognitive Function. Guildford Press, New York 1990.
  19. Zeki, S.: Functional specialization in the visual cortex: the generalisation of separate constructs and their multistage integration. In: Edelman, G.€M., et al. 1990, pp.€85±130.

The Author:

R. Hernegger

Word to HTML by IP GmbH (Werner Eberl, Evi Hummel), 95/09/13.