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Disorders of consciousness are medical conditions that produce cognitive impairment and inhibit consciousness.[1] Some define disorders of consciousness as any change from complete self-awareness to inhibited or absent self-awareness. This category generally includes minimally conscious state and persistent vegetative state, but sometimes also includes the less severe locked-in syndrome and more severe chronic coma.[1][2] Differential diagnosis of these disorders is an active area of biomedical research.[3][4][5] Finally, brain death results in an irreversible disruption of consciousness.[1] While other conditions may cause a moderate deterioration (e.g., dementia and delirium) or transient interruption (e.g., grand mal and petit mal seizures) of consciousness, they are not included in this category.

Characteristics[edit | edit source]

Locked-in syndrome[edit | edit source]

Main article: Locked-in syndrome

In locked-in syndrome the patient has awareness, sleep-wake cycles, and meaningful behavior (viz., eye-movement), but is isolated due to quadriplegia and pseudobulbar palsy. Locked-in syndrome is a condition in which a patient is aware and awake but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles and the body except for the eyes. Total locked-in syndrome is a version of locked-in syndrome where the eyes are paralyzed as well.

Minimally conscious state[edit | edit source]

Main article: Minimally conscious state

In a minimally conscious state, the patient has intermittent periods of awareness and wakefulness and displays some meaningful behavior.

Persistent vegetative state[edit | edit source]

Main article: Persistent vegetative state

In a persistent vegetative state, the patient has sleep-wake cycles, but lacks awareness and only displays reflexive and non-purposeful behavior. It is a diagnosis of some uncertainty in that it deals with a syndrome. After four weeks in a vegetative state (VS), the patient is classified as in a persistent vegetative state. This diagnosis is classified as a permanent vegetative state (PVS) after approximately 1 year of being in a vegetative state.

Chronic coma[edit | edit source]

Main article: Chronic coma

In chronic coma the patient lacks awareness and sleep-wake cycles and only displays reflexive behavior. In medicine, a coma (from the Greek κῶμα koma, meaning deep sleep) is a state of unconsciousness, lasting more than six hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light, sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as comatose. Although, according to the Glasgow Coma Scale, a person with confusion is considered to be in the mildest coma.

Although a coma patient may appear to be awake, they are unable to consciously feel, speak, hear, or move.[2] For a patient to maintain consciousness, two important neurological components must function impeccably. The first is the cerebral cortex which is the gray matter covering the outer layer of the brain. The other is a structure located in the brainstem, called reticular activating system (RAS or ARAS). Injury to either or both of these components is sufficient to cause a patient to experience a coma. The cerebral cortex is a group of tight, dense, "gray matter" composed of the nucleus of the neurons whose axons then form the "white matter", and is responsible for the perception of the universe, relay of the sensory input (sensation) via the thalamic pathway, and most importantly directly or indirectly in charge of all the neurological functions, from simple reflexes to complex thinking. RAS, on the other hand, is a more primitive structure in the brainstem that is tightly in connection with reticular formation (RF). The RAS area of the brain has two tracts, the ascending and descending tract. Made up of a system of acetylcholine-producing neurons, the ascending track, or ascending reticular activating system (ARAS), works to arouse and wake up the brain, from the RF, through the thalamus, and then finally to the cerebral cortex. A failure in ARAS functioning may then lead to a coma. It is therefore necessary to investigate the integrity of the bilateral cerebral cortices, as well as that of the reticular activating system (RAS) in a comatose patient.

Brain death[edit | edit source]

Main article: Brain death

Brain death is the irreversible end of all brain activity, and function (including involuntary activity necessary to sustain life). The main cause is total necrosis of the cerebral neurons following loss of brain oxygenation. After brain death the patient lacks any sense of awareness; sleep-wake cycles or behavior, and typically look as if they are dead or are in a deep sleep-state or coma. Although visually similar to a comatose state such as persistent vegetative state, the two should not be confused. Patients classified as brain dead are legally dead and can qualify as organ donors, in which their organs are surgically removed and prepared for a particular recipient.

Brain death is one of the deciding factors when pronouncing a trauma patient as dead. Determining function and presence of necrosis after trauma to the whole brain or brain-stem may be used to determine brain death, and is used in many states in the US.

Disorders of agency[edit | edit source]

Main article: Disorders of agency

A different sense of consciousness is the ownership of one's experience. Whereas minimally conscious states and persistent vegetative states are medical disorders that affect creature consciousness, disorders of agency affect consciousness in the sense that they rob patients of feelings of ownership over their experiences.

Schizophrenia[edit | edit source]

A common positive symptom of schizophrenia is thought insertion or the experience of thoughts one does not feel agency over. The patient may sometimes be unable to distinguish between their own thoughts and those inserted into their minds. A patient who is diagnosed with this disorder is found to be convinced of their beliefs and unwilling to accept such diagnosis.

Schizophrenia is typically treated with a combination of antipsychotics and psychotherapy.

Anarchic Hand Syndrome[edit | edit source]

Anarchic hand and related alien hand syndrome are neurological disorders in which the afflicted person's hand appears to take on a mind of its own. Anarchic hand syndrome and alien hand syndrome are two similar but separate disorders. In both there are unintended but purposeful and autonomous movements of the upper limb and intermanual conflict. Anarchic hand is usually diagnosed as opposed to alien hand syndrome because it tends to be more associated with motor impairments as the patients acknowledge the hand as theirs but are frustrated by its unintended actions. In alien hand syndrome the individual tends to display more sensory deficits as they dissociate themselves from the hand and its actions, frequently remarking on the hand's behaviour as if it does not belong to them.

Differential diagnosis[edit | edit source]

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Society and culture[edit | edit source]

Locked-in syndrome is chronicled in The Diving-Bell and the Butterfly by Jean-Dominique Bauby and Johnny Got His Gun by Dalton Trumbo.

Research directions[edit | edit source]

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See also[edit | edit source]

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References[edit | edit source]

  1. 1.0 1.1 1.2 Bernat JL (8 Apr 2006). Chronic disorders of consciousness. Lancet 367 (9517): 1181–1192.
  2. Bernat JL (20 Jul 2010). The natural history of chronic disorders of consciousness. Neurol 75 (3): 206–207.
  3. Coleman MR, Davis MH, Rodd JM, Robson T, Ali A, Owen AM, Pickard JD (Sep 2009). Towards the routine use of brain imaging to aid the clinical diagnosis of disorders of consciousness. Brain 132 (9): 2541–2552.
  4. Monti MM, Vanhaudenhuyse A, Coleman MR, Boly M, Pickard JD, Tshibanda L, Owen AM, Laureys S (18 Feb 2010). Willful modulation of brain activity in disorders of consciousness. N Engl J Med 362 (7): 579–589.
  5. Seel RT, Sherer M, Whyte J, Katz DI, Giacino JT, Rosenbaum AM, Hammond FM, Kalmar K, Pape TL, et al. (Dec 2010). Assessment scales for disorders of consciousness: evidence-based recommendations for clinical practice and research. Arch Phys Med Rehabil 91 (12): 1795–1813.

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