I was interviewed for a column appearing in today’s Wall Street Journal on an intriguing case of possible conscious states in a vegetative patient (“There May Be More To a Vegetative State Than Science Thought” by Sharon Begley).
In the case in question, scientists recorded brain activity in a vegetative patient in response to being asked to imagine playing tennis.
Remarkably, this made neurons fire in the premotor cortex, a region that hums with activity when you mentally practice sophisticated movement, from a jump shot to a backhand. 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.
I think that if the same activity also shows up in patients under general anesthesia, then that activity doesn’t suffice for consciousness. The proposal that people under general anesthetic are conscious after all is an intolerable skeptical hypothesis (do you really want to believe that people suffer their major surgeries?). Only a tiny bit of my point got into the article, though:
There also is the possibility that people in other mental states regarded as unconscious, such as patients under general anesthesia, may show similar brain activity, suggests philosopher Peter Mandik of William Paterson University, Wayne, N.J., who studies consciousness.
Lamme et al (1998) suggest that the responses elicited by stimuli in anesthetized animals constitute merely feed-forward activation of representations in perceptual networks and lack feed-back activations from representations higher in the processing hierarchy. I suggested (but it didn’t make it into the article) that a good case for consciousness in the vegetative patient could be made if the following was found in the vegetative but not anesthetized patients: reciprocal activity of higher-level representations (like abstract representations of tennis) and lower-level representations (like motor-representations in a body-centered reference frame) as in Mandik (2005).
(Cross-posted at Brain Hammer)
References:
Begley, S. There May Be More To a Vegetative State Than Science Thought. Wall Street Journal September 8, 2006.
Lamme, V. A. F., et al. (1998). Feedforward, horizontal, and feedback processing in the visual cortex. Current Opinion in Neurobiology, 8, 529 – 535.
Mandik, P. (2005) Phenomenal Consciousness and the Allocentric-Egocentric Interface. In: R. Buccheri et al. (eds.); Endophysics, Time, Quantum and the Subjective. World Scientific Publishing Co.
“I think that if the same activity also shows up in patients under general anesthesia, then that activity doesn’t suffice for consciousness. The proposal that people under general anesthetic are conscious after all is an intolerable skeptical hypothesis (do you really want to believe that people suffer their major surgeries?).”
Why not rather postulate that there are various levels or degrees, or even different varieties, of consciousness, and that those conscious states that persist under anaesthesia are too low-level, or just not of the right sort, to permit the experiencing of pain?
I have argued that one cannot be conscious without having a spatiotopic brain representation of egocentric space. Retinocentric and somatocentric activation patterns cannot do the job. This is because all phenomenal events are experienced from an egocentric perspective. So the fMRI activity found in premotor cortex and parahippocampal gyrus of the vegetative patient after verbal commands is not decisive evidence that egocentric representations (phenomenal/conscious experiences) have been evoked.
References:
Owen, A. M., et al, (2006) Detecting Awareness in the Vegetative State. *Science*, 313, 1402.
Trehub, A., Space, self, and the theater of consciousness. (In press) *Consciousness and Cognition*.
Alan, the answer is because whatever reasons there are for saying they do not experience pain are also the same sorts of reasons for saying they do not experience anything else.
What I find interesting about the case is that it vividly shows how at least some types of “willed” behavior may be preconscious. (Begley wrote that “the vegetative state isn’t what it used to be,” but she might have said the same thing about the will.)