Neural correlates of consciousness

Neural correlates of consciousness (English neuronal Correlates of consciousness ) are brain activities that are associated with processes of consciousness. A common definition is that a neural correlate of consciousness is a neural structure that is minimally sufficient for a state of consciousness. The search for neural correlates is a central project of neuroscientific research on consciousness.

The theories on the neural correlates of consciousness are still largely in a very speculative stage. This is partly due to technical problems such as the lack of temporal and spatial resolution of imaging techniques that measure the activity in the brain. It is also disputed to this day due to the immense complexity of the brain, in which way the brain stores information. Finally, fundamental philosophical problems posed by the already discussed and implemented approaches to research, service also operates in various aspects disagreement.

• 3.1 Conscious and unconscious processing
• 3.2 Binocular Rivalry
• 3.3 lesions

• 4.1 binding problem and 40 Hz oscillations
• 4.2 Neuroanatomical theories
• 4.3 Progress and technical limits
• 4.4 holism and atomism

• 5.1 externalism -off and Cognitive Science
• 5.2 The logic of correlations
• 5.3 Experience and reference to reality

History and Overview

In the search for neural correlates of consciousness is a relatively new part of the field of neuroscience, many discoveries have been made in the last 20 years. Nevertheless, the idea of ​​a correlation of mental and neural structures is quite old. Such a research program within the framework of the Cartesian metaphysics does not make sense, since Descartes proceeded from an immaterial spirit, which at one point only - should interact with the brain - the pineal gland. However, in the late 18th century, Franz Joseph Gall already tried to correlate mental abilities with specific areas of the brain. However, Gall's phrenology could not prevail because it lacked any data that would have been necessary for a successful correlation.

Initial progress presented themselves through the neuropsychological research of the 19th century. Scientists such as Paul Broca and Carl Wernicke is to make identifying brain regions that are associated with certain cognitive abilities succeeded. A major role was played by the examination of patients with well localized lesions of the brain and thus correlated cognitive and / or mental breakdowns. However, the methods of neuroscience of the 19th century were too coarse to lead to a knowledge of the correlates of individual consciousness processes. A fundamental improvement there was only with the introduction of electroencephalography (EEG ) and imaging techniques. By these new methods, it was possible to measure neuronal activity in specific brain regions. This technological revolution has led in recent decades to a rapidly progressing research in the search for neural correlates of consciousness plays an increasingly important role. May be produced for example by transcranial magnetic stimulation (TMS), a magnetic field, non-invasively stimulating regions of the brain.

Despite this progress, there is the search for neural correlates of consciousness even in a largely speculative stage. Although very well confirmed results have been achieved in some areas, such as the incipient development of neural prostheses shows. On the other hand, there is a large disagreement with respect to the interpretation of these results. In addition, these advances affect only parts such as face and form perception or the motor output. At higher cognitive functions such as thinking, there are few generally accepted results.

The neuroscientific research into consciousness has several connections to the philosophy of mind: Firstly, it seems the research to be possible for the first time, to make the biological processes identify connected with the phenomenon of consciousness. At the same time implies the search for neural correlates any particular philosophical position: reductionists can assume that the search for correlates is the first step in the recycling of consciousness on biological processes. Are the neural correlates found, could be reduced to just this correlates of mental states as well. Other theorists understand the search for neural correlates as an alternative to reductive theories: One could describe to them the relationship between mind and brain, without the one due to the other. Even some dualistic positions - such as those of David Chalmers - are compatible with the existence of neural correlates.

What is a neural correlate of consciousness?

The idea of the neural correlate of consciousness seems easy to understand: It searches for structures and processes in the brain that are associated with consciousness. A closer look at the term of the neural correlate of consciousness, however, proves to be quite unclear. This has on the one hand led to very different projects in the search for neural correlates were joined in the research. On the other hand, there has been in recent years, efforts to a disambiguation page, which led to some standardization of language use.

First then must be asked whether it is for a correlate of consciousness in general or correlates of specific processes of consciousness as a perception or a memory, examined. Both objectives can constitute legitimate research projects. A correlative in the first sense would be a state that is sufficient to award a creature consciousness. In neuroscience, however, sought mostly to correlates in the second sense.

Necessary and sufficient conditions

A central theme of the definition is the question of necessary and sufficient conditions. It is easy to see that one can not generally require that a neural correlate is necessary for consciousness, one can not exclude the possibility that different neural states sufficient for a mental state - are - about headaches or a blue perception. But if there are several sufficient conditions, then it may be necessary, none of the states. Since you do not want to exclude by definition more sufficient conditions ( see also multiple realization ), one can of neural correlates do not demand that they represent a necessary condition for consciousness. However, this does not rule out that the empirical research could show that there is only a neural correlate of certain mental processes.

But one can not thereby defining neural correlates that one only demands that they are sufficient for a state of consciousness. The problem is this: When a person is in a state of consciousness, so the overall condition of the brain is sufficient for the state of consciousness. Still do not want to describe the overall state of the brain as a neural correlate of consciousness man - in empirical research one is looking for something Spezifischerem: You are looking for specific processes in the brain that play an essential role for a particular state of consciousness. This additional condition is usually inserted by speaking of " minimally adequate " processes in the brain. The definition is thus: A neural correlate of consciousness is a neural structure that is minimally sufficient for a state of consciousness.

Total and Kernkorrelate

But even this definition is still faced with certain problems. "Minimal sufficiently " can not mean well that the corresponding neural structure is sufficiently different from their surroundings for the state of consciousness completely isolated. Hardly a neuroscientist or philosopher would argue that the appropriate neural structure as isolated would be sufficient for consciousness in a petri dish. But can one still speak of a neural correlate?

The philosopher David Chalmers has proposed to distinguish between a Totalkorrelat and a Kernkorrelat of consciousness. A Totalkorrelat would in any situation sufficiently for a particular state of consciousness. In such Totalkorrelat it would probably be a very comprehensive structure. Even if it is a legitimate research project to look for such a Totalkorrelat, most neuroscientists yet have a specific object. Chalmers proposes to meet these goals by formulating a Kernkorrelats. A Kernkorrelat is not in any conceivable situation sufficiently for a state of consciousness, but it is sufficiently in a normally functioning brain. According to Chalmers, one should understand current neuroscience research projects as a search for Kernkorrelaten. However, the definition of Kernkorrelats has consequences for empirical research: If the Kernkorrelat be bound to normally functioning brains, one has skeptical in finding the Kernkorrelat compared with lesion studies and the like.

Methods and research results

Conscious and unconscious processing

A key element in the search for neural correlates is the recording of neuronal activities. However, it still does not reach the research objective by far with knowledge of the neuronal activity. If a person at a time t perceives a blue object, so many neural activities at the time t nothing to do with the conscious, phenomenal blue perception. It is therefore in a second step, the subset of neuronal activities to determine which part of the neural correlate of consciousness.

An important starting point is the distinction between conscious and unconscious processing. Cognitive Psychological standard techniques such as priming show that mental processes such as perception or memory in parts subconsciously. This has obvious implications for neuroscience: When a person is presented as an object visually, so the brain will process a lot of information on this object, but only part of this information is the person to be aware of. For the search for neural correlates of consciousness, this results in the challenge of the neural processing mechanisms that are associated with consciousness, to separate from the mechanisms that are possible without consciousness.

At this point to distinguish between a posterior and an anterior power the visual perception process is important. Supported by lesion studies led Leslie Ungerleider and Mortimer Mishkin, the distinction between two processing paths a. From the visual cortex two processing streams are to lead away: 1) The ventral stream: Firstly signals in the inferior temporal cortex (IT ) should be conducted, there is an analysis of the properties - such as color, pattern or shape - instead. 2) Dorsal stream: Secondly, according to Ungerleider and Mishkin signals are routed to the rear parietal lobe, where spatial localization of the object takes place. In some recent work Melvyn Goodale and David Milner took over the idea of ​​processing two streams of visual perception and associated with a thesis about consciousness. According to Goodale and Milner processing in the ventral stream is associated with conscious, phenomenal perception, while the dorsal processing occurs largely automatically and without conscious awareness is possible. Neural correlates of conscious visual perception were to be sought according to this theory mainly in the inferior temporal cortex.

The distinction between conscious and unconscious processing processes must be considered in the search for neural correlates. The same is not immediately clear how neuroscience is to succeed, such a distinction. A brain scan can not see what activity is accompanied by consciousness, the same is true for the data of an EEG you. In neuroscience, however, numerous methods have been developed to distinguish these same neuronal activities from each other. Some of the most important methods are described below.

Binocular rivalry

A classical method in the search for neural correlates of consciousness based on the phenomenon of binocular rivalry. As binocular rivalry is defined as the spontaneous change of state of conscious perception. Binocular rivalry occurs when the two eyes presents two different images that can not be integrated into a unified picture. An example: You can present it to the left eye as a red, vertical bar and the right eye a green horizontal bar. When confronted about this, the subject in an alternating sequence is a red and a green bar perceive, but never both images at the same time. The person can not voluntarily control the Wahrnehmungsumschwünge also.

In the search for neural correlates of consciousness one can make use of this phenomenon, by examining, take place which changes the neural events at the moment of the envelope of the perceptual image. Important experiments on this subject were carried out in particular by Nikos Logothetis. The results show that parts of the neuronal processing compared to the perception of reversal are indifferent. Not only that stimulation of the retina can remain the same at different states of perception, even in large parts of the visual cortex of perception swing is not reflected. Rather, there seem to be still present information on both images presented. The situation is different, however, in parts of the temporal lobe, where after Logothetis experiments depends on the activity of the phenomenal percept.

Lesions

For the search for neural correlates of consciousness studies on the effects of brain lesions are important. Can be damaged neuronal structure without the ability is lost to a certain state of consciousness, these neural structure does not seem to belong to the neural correlate of this condition. However, one can not reverse this relationship: the fact that the damage to a neural structure to the loss of a state of consciousness leads does not mean that the neural structure is a part of the neural correlate. This context, one can easily realize by thinking of a lesion of the retina. Are projected from the retina no more information to the visual cortex, the environment can not be perceived phenomenal. But this does not mean that the retina is part of the neural correlate of conscious visual perception: A direct stimulation of neural structures matching could lead to perceptual experiences, even if the retina is damaged.

Of particular importance for consciousness research neuropsychological cases in which conscious experience is disrupted, but the information processing are intact in parts. The most famous case is probably the most researched in particular by Lawrence Weiskrantz cortical blindness ( blindsight ). Patients with cortical blindness perceive themselves as completely blind people, they may subjectively experience no visual input. If you ask the patients, however, to " guess" where a given, visual stimulus is, these patients show benefits that go far beyond a randomized controlled rates. The explanation is that is damaged in cortical blindness not the retina, but the visual cortex. This other processing routes remain intact, allowing a flow of information. Similar phenomena can be identified for other cognitive states. Some patients with aphasia, amnesia or agnosia subjectively experience a loss of language comprehension, memory, or object recognition. Experiments show, however, that some of these patients unconsciously parts can just bring the services to which they no longer seem subjectively able. For the search for neural correlates of consciousness such neuropsychological findings are important. You can help on the one hand, to describe processing pathways that function independently from one state of consciousness and therefore probably not part of the neural correlate of this condition. Secondly, show such cases, what structures are necessary for a particular state of consciousness.

Theories

There are many hypotheses to the question of which form neural structures that correlate states of consciousness. Some researchers suggest that neurons that are part of the neural correlate fire, in a very particular way. Other theories try the neural correlates of consciousness anatomically narrow. The various hypotheses on the neural correlate of consciousness need not always be seen as opposites, sometimes they complement each other even quite good.

Binding problem and 40 Hz oscillations

An influential theory of the neural correlates of consciousness is represented approximately by Francis Crick and Christof Koch and based on ideas that have been expressed in the context of the binding problem. The binding problem arises from the question of how the brain manages to combine the multiple sensory information to uniform perceptions. Experiments and theoretical considerations lead to the conclusion that the brain needs to access information using distributed representations. While it may at first seem plausible that the brain represents an object by a specific neuron: Would such a " grandmother neuron " is active, the object would be ( as the grandmother ) represented by the brain - otherwise not. However, such a form of representation can not be implemented consistently. The set of possible combinations of features means that humans can perceive many different objects almost unlimited. In such a combinatorial explosion may not be kept for each object a particular neuron.

Through distributed representations the brain itself generates a combinatorial explosion. Different neurons should represent no more individual objects, but different characteristics. These features can be combined and so about visually perceived object are represented. Now, however, raises the question of how the brain registers which characteristics are in an object linked. Particularly urgent is this problem when - as is common in everyday life - multiple objects are perceived simultaneously. Suppose that the brain stores the different characteristics of different objects by distributed representations. As it now comes to a correct combination of the features and a unified perception? This question is called the " binding problem ". The neuroinformatics Christoph von der Malsburg developed in the early 1980s, a proposed solution to the binding problem: The brain can link the characteristics by forming representing neurons by synchronous firing of an assembly. This hypothesis attracted international attention several years later, after the research group led by Wolf Singer was able to find experimental evidence for this hypothesis.

Since the emergence of a unified perception is to be explained by the phenomenon of synchronous firing, it is natural to associate it with the conscious experience. Influential is especially a speculative article by Crick and Koch in 1990 become. The two researchers hypothesized that oscillatory activity in the 40 - Hz range is the neural correlate of consciousness. Even today synchronous neuronal activities play a central role in many theories on the neural correlates. However, it is usually assumed that such synchronous firing is not alone sufficient for conscious perception. This has been explained in one of her last, common essays themselves Crick and Koch. "We no longer believe that synchronized firing - such as the so-called 40 -Hz oscillation - is sufficient for the neural correlate of consciousness " If you want to the assembly formation continue connect with the idea of the neural correlate of consciousness, one can restrict the thesis to specific assemblies - such as those that occur in a defined brain region.

With many studies, it was the psychologist Ernst Poppel, Munich, underpin the theoretical and neurophysiological results of this theory and formulate their psychological consequences. E. Pöppel assumes that a synchronized activity of neurons is a necessary condition for making decisions and for the identification of events and also ensures that we can run movements in a regular pace, so speak with a constant pace, go and also can play music. Neuronal oscillations he referred to as the backbone of a temporal coordination of internal roadmap. The time is in the first place made ​​by pawns by the brain for us in rhythmic " time quanta " whose period lasts about 30 msec, but within certain limits is variable.

" Synchronicity creates wholeness " is the principle under which the philosopher Thomas Metzinger with the fundamental question of philosophy brings the correlation theory ( the relation of mind and matter ) in conjunction. In the article " wholeness, homogeneity and time coding ", he made ​​the following assumption: " The postulated as part of the theory of correlation form of time coding is the general integration mechanism that allows - at least in our own type systems - all forms repräsentionaler wholeness are generated. " Why this theoretical assumption is interesting for a philosophical theory of the mind, Metzinger said: "If we have a conceptually consistent and empirically not implausible model of feature binding, ie the formation of representational objects as a form of self-organization, we have namely the first building blocks for a naturalistic theory of consciousness - ie. below for an explanation of "

A comparison of these " correlation theory " with the road to make their statement clear: Those who follow the traffic over screens in the traffic control center of a big city, sees hundreds of car groups that are completely coordinated to jerky, gradually move. The solution are the lights that act rhythmically inhibiting and exciting to the vehicle power. Similarly, act according to the correlation theory of cortical oscillations inhibitory and activating the " stream of consciousness ".

Neuroanatomical theories

A key question in neuroscience is whether it is possible to anatomically isolate the neural correlate of consciousness: Can activities in all brain regions to be part of the neural correlate of consciousness? This is exactly what meant even the psychologist and philosopher William James in the late 19th century. Today's research shows, however, that not all regions are linked in the same way with consciousness processes. Thus, there are extensive lesions of brain regions that do not lead to a deterioration in a state of consciousness. Which neural structures now have a prominent position? The results outlined above on the dorsal and ventral stream and the binocular rivalry lay a central role of the inferior temporal cortex adjacent at least in visual perception.

Another important area is the thalamus, a partial structure of the diencephalon. Even Wilder Penfield declared in 1937: ". All parts of the brain may be involved in the normal, conscious process, but the indispensable substratum of consciousness is probably outside of the cerebral cortex - in the diencephalon " Although many elements of Penfield's theory of consciousness are now considered outdated, plays the diencephalon - and in particular the thalamus - remain a major role in the search for the neural correlates of consciousness. Joseph Arch claims about that awareness was correlated with activity in and around the non-specific thalamic nuclei. Such a theory implies that destruction of this same neuronal structure 'm conscious experience impossible. Gerald Edelman and Giulio Tononi also emphasize the role of the thalamus in their theory. However, according to Edelman and Tononi is the activity in the thalamus alone is not sufficient for consciousness, but this activity must meet certain criteria to be determined by the consciousness. States of consciousness by Edelman and Tononi have two key properties: 1) The different features of a state of consciousness can be experienced as a whole, the experience can not be split into sub-components. 2) In addition, states of consciousness differentiated in the sense that it is possible to experience very many, very different states of consciousness in a short period. According to Edelman and Tononi adequate neuroscientific theory must take into account these characteristics, it should be identified neurophysiological processes, which are characterized by a unifying integration and a corresponding differentiation. Edelman and Tononi go out in the following recursive neural processes whose activation by a kind of loop path ( " reentrant loops" ) is running. The thalamus plays a central role in this loop. However, Edelman and Tononi represented thereby a more holistic approach, so they think that can make any narrowly defined neural sources which will apply as a neural correlate of consciousness. Rather, it always come on a very comprehensive activity in many parts of the brain.

Although the considerable variations between theories about the neural correlate of consciousness in part, most researchers still believe that an anatomical localization is necessary but not sufficient for the finding of neural correlates. In addition to the anatomical distinction the type of neural activity must be determined, which is central to states of consciousness. As this activity is actually present, remains controversial - the ideas of synchronous firing ( see above) and the loop paths are important approaches dar.

When the thalamo - cortical loops ( also running on the " basal ganglia " ) as a cause of cortical oscillations considered, they are not in contradiction to the " correlation theory " but complement, or answer the question of where the synchronous rhythms come.

The function of the thalamus is already in the old metaphor " gateway to consciousness " expressed. Whether this gate is wide open or closed or only slightly open, playing for the content of consciousness, of course, a crucial role.

Progress and technical limits

Considering the current state of research on the neural correlates of consciousness, so there is no uniform picture. In addition to conducting research results are spectacular numerous problems, one of which is not clear whether and how they can be solved. The result is that in the current literature well verified data are not only highly speculative basis theories.

Successes in the search for neural correlates arise in particular from the partially modular way the brain works: It is possible to make some regions in the brain that are selectively active in certain states of consciousness. Examples include the fusiform face area, which is active in visual perceptions and the parahippocampal place area, responsive to homes and visual scenes. Activities in these regions therefore allow conclusions about the content of perception. More detailed knowledge of the current state of awareness can be achieved by measuring the activity of individual neurons. Thus, neurons were found that respond only to the faces of a particular celebrity. In a patient about a neuron was found, which was on average only active when the images of Bill Clinton. At 50 presented images, the neuron responded only to a cartoon of Bill Clinton, his official portrait and a group picture with Clinton. Similar results were also obtained at pictures of other celebrities.

This progress is offset by a number of limitations. These limits are partly technical reasons: The measurement of the activity of single neurons in the human brain is rarely possible. Mostly working with imaging techniques, in particular functional magnetic resonance imaging (fMRI ). Now, however, fMRI provides only a limited temporal and spatial resolution, so it may be that many relevant differences can not be measured. In addition, the fMRI is very expensive and immobile measurements to conscious states are therefore measurements in artificial laboratory situations.

Holism and atomism

In addition to these technical limitations, there are problems that arise from the way the brain works. Although some brain regions can be found, which are highly specialized, so you will still need to pull activities very different regions considered in many states of consciousness. An example: You will not find a neuron in the brain that is active only when one has the idea that the President of Mexico yesterday was unusually badly shaved. Rather, it will be measured a distributed activity in the brain and it is very controversial whether a well circumscribed subset of activities can be found as a neural correlate of thought.

One can distinguish roughly between two hypotheses: Holistic theories claim that it is not possible in most states of consciousness to provide a well- circumscribed number of neurons that can be considered as a neural correlate. In its most radical form of holism asserts that it is possible to specify as a neural correlate of a conscious state only the overall condition of the brain. Atomistic approaches are, however, based on the assumption that relatively small sets of neurons - can be determined as neural correlates - ideally, individual neurons. The dispute between these two approaches is not decided and there are no well in the near future the data to bring about a decision. However, almost all researchers agree that neither a radical holism ( one must always consider all neurons ) nor a radical atomism ( you always have to consider only one neuron ) is plausible. This, however, is not decided whether the brain works in a more holistic or a more atomistic way.

Philosophical problems

Externalism and heeled Cognitive Science

Some researchers exert a more fundamental criticism: They argue that not even suffice the overall condition of the brain to find a correlate of consciousness. One line of argument is based on the externalism in the philosophy of mind Externalisten argue that the content of a thought depends also on the environment in which a person is located. If this theory is true, the overall condition of the brain does not determine what thoughts a person has. Such assertions may seem strange at first glance, but can be better understood if one considers that many of the properties of people depend on the environment and not alone of internal states. The property of being the greatest man in a room depends on the size of the person (internal status ) and the sizes of the other people in the room from ( external conditions ). Externalisten now argue that it is similar to the case with regard Thoughts: A thought about Lily depended about not only by the internal states in the brain but also by the current biological theory. If would be changed to a taxonomic reform of the scope of the genus " Lily", this would the content of the thoughts about lilies change - even though many people would not notice this reform and therefore it would be no change in the brain condition of the people. However, it may be that before the reform of the sentence was true, after the reform wrong: That the content alters, one could see a change in the truth-values ​​" All lilies are less than two meters. ".

Representatives of the so-called embodied or heeled cognitive science argue that one should not be limited to the view of the brain: the example put forward by Alva Noë and Evan Thompson criticism is directed against all the models that include no active action component in their theories. So you can not see ourselves as passive representations of the outside world by Noë and Thompson perceptions. Rather, perception is a fundamentally active process that arises from the interaction with the world. However, if the action component is constitutive of perceptions, it could not deliver the desired results, limited to the brain examination.

The logic of correlations

Correlations are relationships between two or more variables. The fact that A and B are correlated with each other, initially said only that a link between the occurrence of A and B exist. A correlation does not imply that A and B are identical, or that can be reduced to B A. An example may make this clear: the movement of my arm is correlated with the movement of the shadow of my arm, but my arm and its shadow are not identical or reducible to each other. On the other hand, a correlation based on identity. The fact that the actions of Benjamin Franklin are correlated with the actions of the inventor of the glass harmonica, is that Benjamin Franklin and the inventor of the glass harmonica are identical. Philosophical and conceptual one can grasp this fact by saying that correlative relationships are ontologically neutral. A correlation of A and B is possible, when A and B are identical but ( improper correlation) is also possible if they are different entities. It is this ontological neutrality, which has made the search for neural correlates to a widely accepted program - neural correlates are compatible with almost any position in the philosophy of mind. Even dualists can accept neural correlates, they only need to find arguments that there are two ontological essence moderately different entities at A and B.

The so-called materialized or heeled cognitive science ( known under the keywords " enactive " or " sensorimotor " cognition ) criticizes the assumption of neural correlates to the effect that an explanation of the phenomenon of consciousness must always involve the body and especially the specific environment. A second important observation is that it is nichtexplikative relations with correlates. By noting that A and B are correlated with each other, is not made clear why they are correlated. This has consequences for the theory of neural correlates of consciousness. Even if you did find such correlations, has not yet explained why states of consciousness with certain neural processes go hand in hand. For the correlation may in turn give different explanations: the identity of A and B makes a correlation immediately understandable, but A and B could be linked also about by a causal process.

Correlations are ontologically neutral and nichtexplikativ, but they can play a central role in physicalist and reductionist projects. Indeed, it is a plausible assumption that finding a correlation is often the first step in a reductive explanation. This connection can be made clear by a simplified example. Can be found in the chemical analysis of water is always H2O, so this discovery contains no reductive explanation of water. Nevertheless, it can be the first step on the path to such a declaration, such a discovery. Now it is namely to explore the properties of H2O to ultimately explain the properties of water by an adequate chemical theory. If this succeeded, as well as a reductive explanation is successful. Now, one can imagine that finding the neural correlates of the first step in a reductive explanation is in a similar way: Had the neural correlates of consciousness is found, you had the opportunity to study such structures in more detail. A detailed knowledge of this same neuronal processes could lead to some explanation of the phenomenon of consciousness after conception.

Experience and reference to reality

Many philosophers and scientists keep the reductionist optimism just described as exaggerated. They argue that even a detailed knowledge of neural processes are not able to close the explanatory gap between consciousness and the biological processes going. The explanatory gap arises from the fact that states of consciousness are distinguished by special characteristics - notably through the Qualia. Under " qualia " refers to the subjective experience levels of states of consciousness, or about the subjective experience of pain or joy. Now it is argued that no can do, however detailed description of the neural events to understand why something is experienced subjectively. One can show just only that certain activities in the brain occur at about headaches. This is however not explained why it come to the experience of pain in this activity. , This meant, however, that a neuroscientific theory of the experience not explain precisely and therefore can not be reduced.

A similar argument against reductionism based on the concept of intentionality. By " intentionality " is meant that some mental processes refer to objects or situations in the world. It is this reference that thoughts like sentences can be true or false. An example: The idea that Salamanca has the oldest university in Spain, can be related to the historical facts that Salamanca has the oldest university in Spain. It is this relation that makes the ideas come true. Now, some philosophers argue that neural processes are not to Salamanca or fact about Salamanca relate and therefore can not be true or false. Since thoughts have the property of intentionality, neuronal processes, however, are non-intentional, worrying could not be reduced to neural processes. This is also not possible if one has found and explored the neural correlates of thoughts.

Not all philosophers and scientists accept these arguments against the reducibility of consciousness. In particular, the phenomenon of intentionality many researchers consider neuroscientific explanations possible. Often such explanations refer to the concept of representation: Some neuronal processes are representations of facts. Through such representations an intentional reference being manufactured, and the processes could be called true or false. Such explanations assume, however, that you can explain the concept of representation in a non-intentional vocabulary. It remains controversial whether this is possible. The phenomenon of qualia is considered more urgent by many researchers, it is in fact difficult to understand how a reductive explanation of subjective experience salary might look like. Some philosophers, such as Daniel Dennett and Paul Churchland deny the existence of qualia. Many researchers do not want to go as far as Dennett and the Churchlands and still want to hold on to the possibility of a reductive explanation. They often argue with the analogy of the scientific explanation of life: Even the phenomenon of life has long been regarded as a ( scientific ) inexplicable, leading to mysterious sounding positions like that of vitalism. With the advances of modern biology but disappeared in much of the explanatory gap, so that today life is no longer a fundamentally mysterious and inexplicable phenomenon is considered. While some researchers believe they may expect a similar development in terms of awareness, others reject this analogy. Too big, the differences between the then problems with the explanation of life and the problems of today with a declaration of consciousness. However, there are still philosophers ( eg representatives of neo-scholasticism ), which continue to hold not only awareness, but also life only by an immaterial substance such as spirit or the soul, for sufficiently explained.