Consciousness

Consciousness is a quality of the mind generally regarded to comprise qualities such as subjectivity, self-awareness, sentience, sapience, and the ability to perceive the relationship between oneself and one's environment. Philosophers divide consciousness into phenomenal consciousness which is experience itself and access consciousness which is the processing of the things in experience (Block 2004).

Cognitive neuroscience approaches

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 derived from various localized functions that are bound together with a unitary awareness.

Related Topics:
Psychological - Statistical studies - Case studies - Lesion - Stroke - Injury - Surgery - Sense - Cognition - Mind - Bound

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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 an individual 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. Some electroneurobiological interpretations of consciousness characterize this loss of consciousness as a loss of the ability to resolve time (similar to playing an old phonographic record at very slow or very rapid speed), along a continuum that starts with inattention, continues on sleep and arrives to coma and death.

Related Topics:
Persistent vegetative state - Electroneurobiological - Death

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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 (or loss of time resolution) 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 interact with non-mental reality in the first place.

Related Topics:
Epileptic seizure - General anaesthesia - Sleep

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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.

Related Topics:
Midazolam - Anexate

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Many other drugs (such as heroin, cocaine, LSD, MDMA) have a consciousness-changing effect.

Related Topics:
Heroin - Cocaine - LSD - MDMA

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There is a neural link between the left and right hemispheres of the brain, known as the corpus callosum. This link is sometimes surgically severed to control severe seizures in epilepsy patients. This procedure was first performed by Roger Sperry in the 1960s. Tests of these patients have shown that after the link is completely severed, the hemispheres are no longer able to communicate, leading to certain problems which usually arise only in test conditions. For example, while the left side of the brain can verbally descibe what is going on in the right visual field, the right hemisphere is esentially mute, instead relying on its spatial abilities to interact with the world on the left visual field. Some say it is as if two separate minds now share the same skull, but both still represent themselves as a single "I" to the outside world.

Related Topics:
Corpus callosum - Completely severed

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The bilateral removal of the Centromedian nucleus (part of the Intra-laminar nucleus of the Thalamus) appears to abolish consciousness, causing coma, PVS, severe mutism and other features that mimic brain death. The centromedian nucleus is also one of the principal sites of action of general anaesthetics and anti-psychotic drugs.

Related Topics:
Centromedian nucleus - Brain death

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Neurophysiological studies in awake, behaving monkeys performed by neuroscientists (e.g., Steven Wise, Mikhail Lebedev, Nikos Logothetis) point to advanced cortical areas in prefrontal cortex and temporallobes as carriers of neuronal correlate of consciousness.

Related Topics:
Neuroscientists - Mikhail Lebedev

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