Understanding Schiavo, a tutorial for Frist
(shout out to Pharyngula for letting me steal the image)
On Terri's CT scan, the big empty butterfly-shape in the middle are her ventricles, grossly enlarged and filled with fluid; in the healthy brain they are small, shaped like little boomerangs. Terri's cortex is also atrophied (the squiggly blue wormlike lines around the edge of her brain, which you can't see in the normal brain because all the space is filled).
So how do we account for Terri's eye movements? After all, genius physicians like Senate Majority Leader Bill Frist (R-Focus on the Family) can watch a videotape and conclude that because she made eye movements she must have been conscious. Well, Dr. Frist may be one hell of a heart surgeon, but he doesn't know shit about brain physiology.
A portion of the brainstem called the superior colliculus (SC) also receives visual input from the retina. This visual input bypasses the cortex and goes to the SC, which is responsible for automatic visually evoked saccades, which is a fancy way of saying "spastic, jerky eye movement". So basically, the SC plays a role in orienting your gaze to things that draw your attention. This happens reflexively; in fact, higher cortical structures in the frontal lobe are responsible for planned eye movements and active inhibition of those involuntary, reflexive eye movements. One of the most well-characterized higher cortical areas involved in making eye movements is known as the FEF, or Frontal Eye Fields (the occipital lobe, by contrast, tends to do more information processing and less motor control). Without cortical control/inhibition from the FEF and adjacent areas, we would reflexively orient our gaze to every new change in our visual fields!
Now what happens when these higher visual processing centers are destroyed? Your eyes are free to be controlled by your brainstem's SC, meaning that when somebody enters the room, you'll look at them. (I know, it's creepy.) In fact, the brain is wired with all sorts of redundant, partially overlapping control mechanisms for virtually every type of stimulus, explaining why Terri would respond to sounds or touch in a jumpy fashion, as if surprised; her inhibitions were removed when her higher processing centers died, and all that was left were brainstem and spinal reflexes.
Neuroscience is a convoluted field, and this is precisely why we need to let physicians do their jobs even when our common sense tells us something might be up. Heck, even a cardiologist is out of his league when it comes to the finer points of brain function! Now give the cardiologist a conservative