Tuesday, August 02, 2005

The evanescent claustrum of consciousness

The neurology of consciousness | Crick's last stand | Economist.com

We're moving and I tossed out over 100 lbs of medical textbooks -- including 23 year old neuroanatomy notes. I don't remember much attention being paid to the 'claustrum' back then:
... The immodesty that carried Crick to the discovery of the structure of DNA in 1953 clearly never left him. His latest paper (and his last, for he died in 2004) proposes to explain, of all things, the neurological basis of human consciousness.

Mechanistic explanations of consciousness are hard to come by because consciousness is so poorly understood. Indeed, it is one of the few unexplained phenomena that are genuinely mysterious rather than merely problematical. But Crick, together with his long-time collaborator Christof Koch, of the California Institute of Technology in Pasadena, focused on a part of the mystery that seems tractable. This is the integrated nature of conscious sensation.

As the two researchers put it in their paper, which was published this week in the Philosophical Transactions of the Royal Society, “When holding a rose, you smell its fragrance and see its red petals while feeling its textured stem with your fingers.”

The part of the brain that caught the two researchers' interest is the claustrum, a thin sheet of grey matter that lies concealed beneath part of the cortex (the outer covering of the brain that carries out the computations involved in seeing, hearing and language).

The key to the researchers' claim is that most, if not all, regions of the cortex have two-way connections to the claustrum, as do the structures involved in emotion. It is plausible that the smell, the colour and the texture of the rose, all processed in different parts of the cortex, could be bound together into one cohesive, conscious experience by the claustrum. The authors liken it to a conductor who synchronises and co-ordinates various parts into a united whole.

Thus far, this is mere anatomical speculation fuelled by the fact that very little is known about what the claustrum actually does. Crick hoped that his final paper would inspire researchers to begin to develop molecular techniques to disable the claustrum in animals to observe the aftermath...
Crick must have known the end was near, and his fame and privilege allowed him to publish something so speculative. All the same, the claustrum does sound fascinating. I hope the proposed animal studies will not require chimpanzees to perform ...

The Caltech connection is interesting; I have always recalled my former roommate, Armando's, intuition that consciousness was deeply connected to motor function (1978). The claustrum, I believe, is usually described as a part of the motor cortex. One might speculate that the evolution of consciousness bears the same relationship to the motor cortex as the evolution of memory bears to the neuroanatomy of scent. Such speculation is grand fun.

If indeed the claustrum has some sort of role in conscisousness, it should be possible to study it in disorders of consciousness, such as coma and autism. Of course we will invariably that some people are more conscious than others. (With great effort I resist the temptation to relate consciousness to political choices.)

Alas, bad news on another front suggests consciousness probably does not improve with age. Much of our body regenerates, but C14 data suggests most of our brain does not. Thus brain may deteriorate even more quickly than our bodies. Not good news for those who think the retirement age may be substantially extended.

So, as we age, does our consciousness thus decline?

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