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Table of contents
1 Introduction
2 Consciousness and language
3 Cognitive neuroscience approaches
4 Philosophical approaches
5 Quantum Mechanical Approaches
6 Other relevant entries
7 Further reading
8 External links


Agreed upon definitions of consciousness are notoriously difficult to come by. While no single definition for the term 'consciousness' exists, it is generally regarded to comprise qualities such as self-awareness, sentience, sapience, and the ability to perceive the relationship between oneself and one's environment. In common parlance, consciousness denotes being awake and responsive to one's environment; this contrasts with being asleep or being in a coma.

Many cultures and religious traditions place the seat of consciousness in a soul separate from the body. Converesely, many scientists and philosophers consider consciousness to be intimately linked to the neural functioning of the brain.

An understanding of necessary preconditions for consciousness in the human brain may allow us to address important ethical questions. For instance, to what extent are non-human animals conscious? At what point in fetal development does consciousness begin? Can machines ever achieve conscious states? These issues are of great interest to those concerned with the ethical treatment of other beings, be they animals, fetuses, or in the future, machines.

Consciousness and language

Because humans express their conscious states using language, it is tempting to equate language abilities and consciousness. There are, however, speechless humans (infants, Kaspar Hauser, aphasics), to whom consciousness is attributed despite language lost or not yet acquired. Moreover, the study of brain states of non-linguistic primates, in particular the macaques, has been used extensively by scientists and philosophers in their quest for the neural correlates of consciousness.

Cognitive neuroscience approaches

Several studies point to common mechanisms in different clinical conditions that lead to loss of consciousness. Persistent vegetative state (PVS) is a condition in which a person loses the higher cerebral powers of the brain, but maintains sleep-wake cycles with full or partial autonomic functions. Studies comparing PVS with healthy, awake subjects consistently demonstrate an impaired connectivity between the deeper (brainstem and thalamic) and the upper (cortical) areas of the brain. In addition, it is agreed that the general brain activity in the cortex is lower in the PVS state.

Loss of consciousness also occurs in other conditions, such as general (tonic-clonic) epileptic seizures, in general anaesthesia, maybe even in deep (slow wave) sleep. The currently best supported hypotheses about such cases of loss of consciousness focus on the need for 1) a widespread cortical network, including particularly the frontal, parietal and temporal cortices, and 2) cooperation between the deep layers of the brain, especially the thalamus, and the upper layers; the cortex. Such hypotheses go under the common term "globalist theories" of consciousness, due to the claim for a widespread, global network necessary for consciousness to exist in the first place.

Brain chemistry affects human consciousness. Sleeping drugs (such as Midazolam = Dormicum) can bring the brain from the awake condition (conscious) to the sleep (unconscious). Wake-up drugs such as Anexate reverse this process. Many other drugs (such as heroin, cocaine, LSD, MDMA) have a consciousness-changing effect.

Philosophical approaches

Philosophers distinguish between phenomenal consciousness and psychological consciousness. Some suggest that consciousness resists or even defies definition. There are many philsophical stances on consciousness, sometimes known as 'isms', including: behaviorism, cognitivism, dualism, functionalism, phenomenalism, physicalism, pseudonomenalism, and mysticism.

Phenomenal consciousness

There is, in the view of very many philosophers, one mental function that accompanies some, or perhaps all, mental events, namely, consciousness. In a philosophical context, the word "consciousness" means something like awareness, or that a mind is directed at something. (That sounds more like a definition of that philosophical term "intentionality" often referred to with the layman's term "aboutness".) So when we perceive, we are conscious of what we perceive; when we introspect, we are conscious of our thoughts; when we remember, we are conscious of something that happened in the past, or of some piece of information that we learned; and so on.

In this philosophical sense of the word "conscious", we are conscious even when we are dreaming; we are conscious of what's happening in the dream. But sleep researchers believe there is a sleep stage that happens, called "deep sleep", in which apparently we are not conscious of anything in any sense. No mental processes that involve consciousness in an ordinary or in a philosophical sense are going on. So dreamless deep sleep is an instance in which one is alive and one's brain is functioning, but there are no mental events occurring in which there is any element of consciousness.

Modern investigations into and discoveries about consciousness are based on psychological statistical studies and case studies of consciousness states and the deficits caused by lesions, stroke, injury, or surgery that disrupt the normal functioning of human senses and cognition. These discoveries suggest that the mind is a complex structure of various localized functions held together by a unitary awareness.

There has been some debate about the following question: Must one be conscious, in the philosophical sense, whenever a mental event occurs? For example, is it possible to have a pain that one does not feel? Some people think not; they think that in order for something to be a pain, one has to feel it and hence be aware of it. Similarly, if anything is a thought, then one has to be aware of that of which one is thinking (indeed, that seems nearly a tautology); if there is no consciousness, then one is not thinking. This raises these questions: do mental events necessarily involve consciousness? What about functioning of the brain of which we are unaware?

Suppose we answer "No." Then, of course, what we'd be saying is that there are some mental events that do not include an element of consciousness. These events are going on even though we aren't aware of them. In other words, part of the mind is unconscious. Cognitive scientists believe that many cognitive processes are unconscious in this manner; we are aware of only some of the events that are occurring in our minds.

Some view consciousness as an emergent phenomenon, somehow arising from a hierarchy of unconscious processes. These are fairly recent views, made popular only after Freud.

Quantum Mechanical Approaches

The physicist Roger Penrose, in his book The Emperor's New Mind, argued for a quantum mind approach, suggesting that non-local quantum mechanical effects within sub-neural structures give rise to conscious states. He has argued for the need for a fundamentally new physics in order to explain consciousness.

Penrose was not the first to suggest a link between consciousness and QM; Michael Lockwood and Henry Stapp got there first, and so did Brian Flanagan. Before them there was Bohr, the father of quantum mechanics (QM), who, as David Bohm tells us, "suggests that thought involves such small amounts of energy that quantum-theoretical limitations play an essential role in determining its character." Also of interest are the ideas of Weyl, Wigner, and Schrodinger.

However, the 'hypothesis' that consciousness relies upon quantum mechanics is a view discounted by all but a tiny number of scientists. No real evidence has been found to support any relationship between quantum mechanics and the phenomenon of consciousness.

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