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Consciousness is notoriously difficult to define or locate. Many cultures and religious traditions place the seat of consciousness in a soul separate from the body. Conversely, 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.
Because humans express their conscious states using language, it is tempting to equate language abilities and consciousness. There are, however, speechless humans (infants, feral childrenFeral children are children who have lived isolated from human contact starting from a very young age. Their separation from society may be the result of being lost, abandoned, or even taken away by animals. Sometimes abandonment is apparently due to pare, aphasicsAphasia is a loss or impairment of the ability to produce or comprehend language, due to brain damage. It is usually a result of damage to the language centres of the brain and can be caused by a stroke or physical injury. Depending on the area and extent), 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 macaquessee text The macaques form the genus Macaca of Old World monkeys. Aside from humans (genus Homo , the macaques are the most widespread primate genus, ranging from northern Africa to Japan. Nineteen macaque species are currently recognised, and they includ, has been used extensively by scientists and philosophers in their quest for the neural correlates of the contents of consciousness.
Several studies point to common mechanisms in different clinical conditions that lead to loss of consciousness. Persistent vegetative stateA persistent vegetative state (or PVS) is a condition of patients with severe brain damage in whom coma has progressed to a state of "wakefulness without awareness". The term was introduced by two doctors in 1972 to describe a syndrome that seemed to have (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. Some non-Angloamerican traditions in electroneurobiology (a technical term to search the Web for them) view 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.
Loss of consciousness also occurs in other conditions, such as general (tonic-clonic) epileptic seizures, in general anaesthesiaIn modern medical practice, general anaesthesia is a complex procedure involving: preanaesthetic assessment administration of general anaesthetic drugs cardirespiratory monitoring analgesia airway management fluid management Preaneasthetic evaluation Moni, 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.
Brain chemistry affects human consciousness. Sleeping drugs (such as MidazolamMidazolam also known by the trade name Versed, is an benzodiazepine with an imidazole structure. Used commonly as an anxiolytic, amnesiac and sedative, this medication provides an effect similar to diazepam, but with a quicker onset and shorter duration. = 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.
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.
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