Disorders of consciousness

1. What two parts of the brain are responsible for consciousness?
2. What is a coma? How does it show up on EEG?
3. What is the mortality for comas lasting >6hrs? When does a coma generally evolve into a vegetative state (VS)? How can you tell this evolution has occurred?
4. What is a VS? When is it called a persistent VS or a permanent VS?
5. What are the characteristics of VS?
6. What is the neuropathology behind VS?

Answers:
1. The cerebral cortex and the ascending reticular activating system (cell bodies in the upper brain stem that project to cortex via thalamic and extrathalamic pathways).
2. A coma is an unconscious state in which the patient can't be aroused and there is no self or environmental awareness, no spontaneous purposeful movement, no localization of noxious stimuli, no language comprehension. EEG shows no sleep-wake cycles.
3. After >6hrs in coma, 50% patients die. In 2-4 weeks, comas evolve into vegetative states, which signals the return of brain stem arousal mechanisms in the face of thalamic, cortical and/or subcortical damage. Coma and VS are both characterized by absence of cerebral cortex activity. Transition to VS is signaled by eye opening, visual tracking, and spontaneous control of autonomic functions (respiration, CV, thermoregulation, neuroendocrine).
4. VS is loss of capacity to interact with environment despite preserved spontaneous or stimulus-induced arousal. It is called persistent VS >1 month after brain injury. It is called permanent VS either >3 months after nontraumatic brain injury or >12 months after TBI.
5. In VS, patient will open eyes, EEG shows sleep-wake cycles, no purposeful behavior, no signs of communication.
6. VS is related to diffuse cortical injury. Bilateral thalamic lesions are prominent findings.