Wednesday, August 26, 1998 Published at 06:40 GMT 07:40 UK
We think therefore I am
Human brain tissue: Could contain many micro-consciousnesses
By John Newell of BBC Science
The philosopher Rene Descartes said "I think, therefore I am." Research carried out by neurologists in London now suggests that the famous dictum should be rephrased as, "We think, therefore I am."
The new idea is that, far from being a single entity, each person's consciousness is built up from many separate mini-consciousnesses at different levels in the brain.
"One is that it has nothing to do with the nervous system, it's above it as it were. That's the way philosophers have on the whole thought about it.
"The other is the approach of serious scientists who think consciousness is the product of activity in the brain. But they have tended to think of it as a unified thing, a unity."
Specialised areas of perception
But Semir Zeki and his colleagues do not agree.
"Our hypothesis is that there are many many different consciousnesses in the brain, which we call micro-consciousnesses, and that these are the results of activities at different stages in the brain.
"There are many stages leading to each area of the brain, and each area is specialised for a different kind of perception. One deals in colour, one in lettering, one in faces and so on.
"Each one of these can have a conscious correlate. The brain generates all these micro-consciousnesses and then they are bound together into a super consciousness."
One bit of evidence for the theory is that when one of the systems is destroyed, for example when the part of the brain responsible for colour perception is destroyed, then the person concerned loses the ability to see in colour but their vision is not otherwise affected.
On the other hand, brain damage that affects the whole visual centre but spares the colour centre will result in a patient who is blind, but who can nevertheless visualise colours.
If consciousness was a single entity, not an assembly of micro-consciousnesses, then you would expect the whole visual system to be affected by damage. But it isn't.
The other bit of evidence was produced by Semir Zeki and his colleague Andreas Bartels themselves. They measured the speed with which normal humans consciously perceive colour, form and motion.
They found that humans see colour about eighty thousandths of a second before they see form, and form about the same time before they see motion, even when all three are presented simultaneously.
Since each such visual percept is a conscious event, the difference in timing implies that consciousness is made up of separate conscious events. But questions remain to be answered.
"We are still left with the puzzle of what it is in the firing of the brain cells [the messages they send] that results in the experience of consciousness for each system.
"That has by no means been solved. But I think the philosophical view of consciousness will have to be modified quite substantially, by thinking about not one unique entity but many, many entities."
If the theory is accepted, then in the future, if someone suffers a brain injury, then they may be thought of as having some of their micro-consciousnesses affected but not others, rather than having their overall consciousness affected.
Eventually this may affect the way in which some mental illnesses as well as brain damage are thought of, and even the ways in which they are treated. But that is probably many years away.