Coma: Characterized by the absence of arousal and consciousness, it is an unresponsive state in which the patient’s eyes are closed, he or she is not able to be aroused, and is unaware of himself or herself and his or her surroundings. Unlike the vegetative state, stimuli in comatose patients do not produce spontaneous awakening and eye opening. To be distinguished from syncope, concussion, and other transient states of impaired consciousness, coma must last at least 1 hour. Overall, surviving comatose patients awaken and recover within 2 to 4 weeks. This recovery time can be longer than the vegetative or minimally conscious state, or it can be short or long before full consciousness is restored. Vegetative state: Patients in a vegetative state can awaken but are unaware of themselves and their surroundings. Persistent vegetative state is defined as remaining in a vegetative state for 1 month after acute traumatic brain injury or non-traumatic brain damage. It does not imply irreversibility. A permanent vegetative state is irreversible. PVS is defined by the Multi-Society Task Force as remaining in a vegetative state 3 months after a non-traumatic brain injury or 12 months after a traumatic brain injury. The British Medical Association (BMA) considers the following clinical criteria to be met: no evidence of awareness of self or environment; no response to visual, auditory, tactile, or other stimuli indicating a conscious purpose; inability to understand language or make meaningful expressions; a distinct sleep-wake cycle; and preserved hypothalamic and brainstem function to maintain respiratory and circulatory functions. Minimal consciousness state: manifests as limited but clear awareness of self and surroundings, based on repeatability or persistence, with at least one of the following behaviors: execution of simple instructions; expression of yes/no responses with gestures or speech (whether correct or not); comprehensible speech; purposeful behavior (including actions or valid behaviors related to environmental stimuli, not caused by reflex activity). The emergence of a minimally conscious state is defined as the ability to communicate or use objects functionally. It is more likely to progress further than a persistent vegetative state. However, there are some patients who are permanently in a minimally conscious state.