What is a defining feature of coma?

A defining feature of coma is deep prolonged unconsciousness. In a state of coma, an individual cannot be aroused and fails to respond to stimuli in a purposeful manner. They are unresponsive to both external stimuli (like sound or touch) and internal stimuli (like pain). This condition represents a severe alteration in consciousness where the person does not exhibit awareness of themselves or their environment.

While other states like vegetative states or minimally conscious states might present some level of responsiveness, coma is characterized by the absence of such awareness. The duration of coma can vary significantly; however, it is generally understood as a profound and extended state of unresponsiveness, distinguishing it from states involving shorter lapses in consciousness or reduced sensory perception. Thus, deep prolonged unconsciousness is the hallmark of a coma, making it the correct answer.