Ask the expert

Q Can anything help a person in a coma?

A Coma is a state of prolonged deep unconsciousness lasting at least hours, caused by severe and extensive loss of brain function.

It can have a variety of causes and the underlying cause is critical in determining whether or not the coma can be reversed.

One can recover from comas arising from metabolic causes (such as diabetes or drug intoxication) or profound hypothermia (abnormally low body temperature).

However, it is rare to recover from a coma due to a massive stroke, massive circulatory failure (such as a heart attack that causes oxygen starvation to the brain), brain trauma, brain complications of cancer or a serious brain infection.

Regardless of the underlying cause of coma, the initial unconsciousness does not persist beyond weeks, giving way to a "persistent vegetative state", where the eyes are open, giving the semblance of normalcy, but the patient stares blankly into space, making few, if any, intelligible responses.

There are many false beliefs about recovery from coma arising from desperation.

One of these is that speaking to a person will help. A person who is lightly asleep or in a light state of unconsciousness has preferential response to his name relative to other sounds but, by definition, a person in a coma is unresponsive to the external environment.

• Professor Michael Chee, director, Centre for Cognitive Neuroscience, Duke-NUS Medical School.

• Have a burning science question? E-mail us at STscience@sph.com.sg

A version of this article appeared in the print edition of The Straits Times on February 26, 2016, with the headline 'Ask the expert'. Print Edition | Subscribe