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Understanding comas and consciousness

Dr. Michael A. Williams is medical director of the Sandra and Malcolm Berman Brain & Spine Institute at LifeBridge Health.
Dr. Michael A. Williams is medical director of the Sandra and Malcolm Berman Brain & Spine Institute at LifeBridge Health. (Courtesy of LifeBridge Health, Baltimore Sun)

Bobbi Kristina Brown, daughter of the late Whitney Houston and Bobby Brown, has spent more than a month in a medically induced coma since being discovered Jan. 31 unconscious and face-down in a bathtub. People can survive a coma, with their chances largely depending on the level of brain damage they suffered, according to Dr. Michael A. Williams, medical director of the Sandra and Malcolm Berman Brain & Spine Institute at LifeBridge Health. He explains the meaning of consciousness and the different states of unconsciousness.

What is the definition of consciousness?

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Consciousness is defined as awareness of oneself and the environment. Consciousness can be divided into wakefulness (being awake) and awareness (being aware). When evaluating consciousness, neurologists determine that patients are awake when their eyes open spontaneously or when they open in response to a stimulus. Neurologists determine that patients have awareness if they are able to perceive a stimulus in their environment and make a response that requires the ability to think, such as holding up two fingers when asked to do so.

What part of the brain is responsible for wakefulness and awareness, and what happens when they are damaged?

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The part of the brain responsible for wakefulness is the reticular activating system (RAS), a group of neurons located in the upper brainstem. When the RAS stimulates the brain, a person's eyes open. If the RAS is not functioning normally, the eyes will not open. Although wakefulness is necessary for consciousness, wakefulness alone is insufficient for consciousness. Signs of awareness must also be present.

Awareness is the ability to perceive oneself and the environment and to respond to it purposefully. However, when awareness is absent, a patient is capable of only automatic reflex responses. By examining patients carefully, neurologists can distinguish between purposeful and reflex movements that may appear similar.

The parts of the brain responsible for awareness are the neurons (brain cells), mostly in the cerebral cortex — the grey matter at the surface of the brain. The billions of neurons make trillions of connections to each other via axons (communicating projections) in the white matter. Awareness is not a function of any single area of the brain; it requires the coordinated function of many different brain areas. Severe and widespread injury to the cortex, white matter, or other areas of the brain will result in unconsciousness, even if the RAS is functioning normally. However, consciousness is possible when only limited areas of the cortex are injured.

What are the different states of unconsciousness?

The three major disorders of consciousness are coma vegetative state, and minimally conscious state. In coma, which typically is present for the first one to two weeks after brain injury, patients are not awake or aware, meaning that they do not open their eyes, have only reflex responses and are unaware of those around them.

If a coma lasts more than two or three weeks, it evolves into the vegetative state. In this state, unlike coma, wakefulness is present, which means that patients' eyes open either spontaneously or in response to stimulus. However, as in coma, awareness is not present. If the vegetative state persists for more than three to six months, the term persistent vegetative state is applied.

If patients recover from the vegetative state, a condition known as the minimally conscious state may occur. In this state, patients may have subtle or inconsistent purposeful responses, such as attempting to speak or reach out for something. Some of these patients continue to improve, but others remain in this state and have severe neurologic impairment.

What are the chances that patients regain consciousness from each state?

Doctors and family members are understandably concerned when patients are in a coma. However, the presence of coma early after injury does not always predict whether patients will regain consciousness, stay in the vegetative state or die despite treatment. Patients in coma as a result of severe brain injury, such as with drowning or cardiac arrest, are less likely to regain consciousness, particularly if the coma lasts more than two weeks and evolves into the vegetative state.

The less severe the brain injury, the better the chances that patients will regain consciousness. Even though some may be in coma for more than two weeks, with time, they may regain consciousness.

An individual patient's potential to regain consciousness is difficult to predict in the first few days of coma, and doctors must carefully and repeatedly look for signs of worsening or improvement to determine the prognosis.

Patients' ability to recover from coma can be enhanced with the right care from appropriate specialists during each stage of coma and recovery. Initially, patients are treated in intensive care units with efforts to support the brain. After patients leave the hospital, they benefit from therapies at specialized rehabilitation centers.

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