Vegetables

In the May edition of Scientific American, there's an article about consciousness of coma / vegetable patients. It's titled "Eyes Open, Brain Shut", and written by Steven Laureys.

When people slip into a coma, they don't open their eyes, but some of them may show some reflex movements of the limbs. If people come out of their coma, they can enter a vegetative state, in which they remain unconscious; they are awake, but not aware. For instance, they have sleep/wake cycles, and some form of movement which is not purposeful but only reflexive.


How do you measure the awareness of a patient? How do you diagnose a vegetative state? This may be helpful to distinguish between patients who may recover or not. A MRI or CT scan can show how damaged the brain is, but it's impossible to see if the patient has some level of consciousness. An EEG (ElectroEncephaloGram) measures the brain's electrical activity which is able to show the state of wakefulness, but not a reliable change in awareness.

With the use of a PET (Positron Emission Tomography) scanner, the metabolic activity can be viewed (measured by its consumption of glucose). In the vegetative state this metabolism is lower. When the patient is at rest, it can't successfully distinguish between the vegetative and minimally conscious state. This changes when external stimuli like pain and spoken words are added to the equation. This makes sense, because the awareness in a vegetative state is lower then in a minimally conscious state.
Persons in a vegetative state may very well understand commands: there is a "conscious linguistic processing in the vegetative patient". Furthermore, in some "mental imagery tasks", the patient understood the tasks (tasks like: imagine walking through the rooms of your house). These responses were indistinguishable from that seen in the healthy subjects. However, there may be a possibility that the patient was transitioning to a minimally conscious state, in which the awareness is raised.

It's a well written article; so if you have access to it, I'd recommend reading it.