karl_lembke (karl_lembke) wrote,

Vegetative States

(From the Science Journal column of the Wall Street Journal, Sept 8, 2006 — subscription required for access.)

Sharon Begley has a weekly science column for the WSJ, and this week, she looks at the hot research on the brain of one young accident victim who's been diagnosed as being in a persistent vegetative state (PVS).

One of the problems with PVS, highlighted in the case of Terri Sciavo, is that:
Patients in a vegetative state open their eyes and seem to be awake, yet show no sign of being aware of themselves or of their surroundings. They don't move or respond to stimuli except in a reflexive way. [Terri's] smiles and reflexes convinced her parents, not to mention many powerful politicians, that she was conscious. But in a vegetative state, the mind is thought to be AWOL.

Now, here's another patient in a PVS, only this one's been examined using functional MRI (fMRI). fMRI uses a tracer while MRI images are made to detect activity in certain tissues, particularly the brain. The technique is precise enough to detect increases and decreases of activity in the brain, and has been used to explore what happens in the brain when people undertake various mental tasks.
In the case of this patient:
When the scientists spoke to her ... her brain registered activity in regions responsible for decoding language, just as the brains of normal volunteers do. When they used sentences with homonyms, which require more complicated semantic processing, the appropriate parts of her brain lit up, again, just like the healthy brains.
Either response might be dismissed as automatic and therefore unconscious. After all, some people in a vegetative state retain "islands" of preserved neural function...but not in areas involved in higher mental function.
So they asked her to imagine playing tennis. Remarkably, this made neurons fire in the premotor cortex, a region that hums with activity when you mentally practice a sophisticated movement...
Then they asked her to imagine walking through each room of her house. This time her parahippocampal gyrus, which generates spatial maps, became active, again just as in healthy volunteers.

Neither of these responses is in any automatic. They require "the willed, intentional action of the participant", according to researchers.
But we can't generalize this finding to other PVS patients.
Indeed, 60 previous patients in a vegetative state show no such brain activity...
When the Terri Sciavo fight was going on, it occurred to me that PVS is the 21st century's version of the fear of being buried alive. What we're looking at is the fear, hinted at in this case, of being conscious at some level, but of being locked in a body that won't do what you tell it to do.
Fear of live burial waned with the advent of techniques for determining with certainty whether a patient was actually dead (and of course, practices like embalming, following which the patient is certainly dead). The fear of being wrongly diagosed in PVS will fade after we develop techniques for reliably determining whether or not the mind is AWOL.
Most scientists believe that consciousness means knowing that you know, even being conscious that you are conscious. Figuring out how to determine that has only just begun.
Tags: medicine, politics

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