In the April Report on Progress “Waking Up from Coma: New Treatments, New Hope,” Dana Alliance member Clifford B. Saper, M.D., Ph.D., explains current research on comas and what happens to the brain in this state.
“After a couple of weeks in coma due to damage to the arousal system, the remaining structures in the brainstem and the forebrain reorganize their activity, and the patient recovers apparent wake-sleep cycles, with eye opening and faster EEG waves during the day. However, if the cerebral cortex itself has been damaged, for example by severe traumatic brain injury or a period of not getting enough oxygen, then the patient will go through “empty” wake-sleep cycles, where the eye opening is not accompanied by signs of cognition (responding to events in the environment). After a month in such a state, the patient is said to be in a “persistent vegetative state.”
Dr. Saper focuses on patients that show clear, although minimal sign of cognitive, recovery because they have a greater potential for more substantial recovery.
You can find a list of all the Reports on Progress here: http://dana.org/news/reportonprogress/