Self Comes to Mind

the brain stem, and sometimes the damage trespasses into the hypothalamus. Most commonly this is caused by a stroke. We know that the damage must be located in the back part of the brain stem, the tegmentum, and more specifically in its upper tier. The upper tier of the tegmentum houses nuclei involved in life regulation but not those that are indispensable to maintaining breathing and cardiac function. In other words, when the damage involves the lower tier of the tegmentum as well, the result is death, not coma.
    When the damage occurs in the front part of the brain stem, the result is also not coma but rather locked-in syndrome , a horrible condition in which the patient is entirely conscious but almost completely paralyzed. The patient can communicate only through blinking, sometimes with only one eye, sometimes through the upward movement of one eye. Yet they see perfectly well whatever is brought in front of their eyes and thus can read. They can hear perfectly well too and appreciate the world in fine detail. Their prison is nearly complete; only a dulling of the background emotional reactions somehow transforms a terrifying situation into a painful but barely tolerable one.
    We know about those patients’ unique experiences from a few dictated reports that some intelligent and observant patients had the courage to pursue, with expert help. The reports were not really dictated but rather “blinked,” one letter a blink. I used to think that Lou Gehrig’s disease (amyotrophic lateral sclerosis) was the cruelest of neurological diseases. In Lou Gehrig’s disease, which is a degenerative brain condition, equally conscious patients gradually lose the ability to move, to speak, and eventually to swallow. But once I saw my first patient with locked-in syndrome, I realized that it manages to be worse. The two best books by locked-in patients are small and simple but humanly rich. One of them, by Jean-Dominique Bauby, was turned into a surprisingly accurate movie, The Diving Bell and the Butterfly , directed by the painter Julian Schnabel. It offers nonspecialists a satisfactory documentary of the condition. 17
    Coma often transitions into a somewhat milder condition called vegetative state. The patient is still unconscious, but as previously noted the condition differs from coma on two counts. First, patients have sleep-wakefulness alternations, and when sleep or wakefulness occurs, its signature electroencephalographic pattern is present too. The patients’ eyes can be open during the awake part of the cycle. Second, the patients do produce some movements and may respond with movements. But they do not respond with speech, and the movements they execute have no specificity. Vegetative state can transition into recovery of consciousness or remain stable, in which case it is called persistent vegetative state. In addition to damage to the brain-stem tegmentum and hypothalamus, which is the typical pathology of coma, vegetative state can result from damage to the thalamus and even from widespread damage to the cerebral cortex or underlying white matter.
    How do coma and vegetative state relate to the PMC role, given that the causative lesions are located elsewhere? That question has been addressed in functional imaging studies aimed at investigating how generalized or restricted the functional changes are in the brain of patients in those conditions. The usual suspects do turn up, as revealed by major reductions of the function of the brain stem, the thalamus, and the PMCs, but the reduction of local metabolic rate for glucose observable at the PMCs is especially pronounced. 18
    But there is another relevant finding to report. Patients in a coma commonly either die or improve quite modestly into a persistent vegetative state. Some patients, however, are more fortunate. They emerge gradually from their state of profoundly impaired consciousness, and, as they do, the most significant changes in brain metabolism occur at the PMCs. 19 This suggests that the level of activity in this area is well correlated with the level of consciousness. Given that the PMCs are so highly metabolic, one might be tempted to dismiss this finding as the result of wholesale improvement of brain activity. The PMCs would improve first merely because of their high metabolism. But that would not explain why consciousness is regained at the same time.
A Closing Note on the Pathologies of Consciousness
     
    The pathologies of consciousness