26 March 2011

Constructing Your Own Cartesian Theatre

Cartesian Theater

The Cartesian Theatre is the place inside your head where you sit and watch the world unfold before your very eyes. Well, not really. In order for cognitive scientists to better understand how our brains create an interactive conscious experience, they actually had to demolish the Cartesian Theatre in order to assemble a structure of brain and mind that better fit with the research.

The search for the seat of consciousness has been a long and tumultuous journey, and by no means have humans come near the hidden prize. But some ideas are better than others -- some have thought the thing through more clearly than others, incorporating more of the confirmed research data into more elegant theories.

In "Self Comes to Mind," Antonio Damasio reveals some of his deepest and most recent ideas regarding the origin of the conscious self. It is worth quoting from Chapter 9 of the book to illustrate Damasio's search for the origin of self:
Several possible structures come to mind, but only a few can be seriously considered. An important candidate is the thalamus, a perpetual presence in any discussion of the neural basis of consciousness, specifically its collection of associative nuclei. The intermediate position of the thalamic nuclei, between the cerebral cortex and the brain stem, is ideal for signal brokering and coordination.

Although the associative thalamus is busy enough constructing the background fabric of any image, it plays a very important, albeit perhaps not the lead, role when it comes to coordinating the contents that define the autobiographical self. I will say more about the thalamus and coordination in the next chapter.

What are the other likely candidates? A strong contender is a composite collection of regions in both cerebral hemispheres that is distinguished by its connectional architecture. Each region is a macroscopic node located at a major crossroads of convergent and divergent signaling. I described them as convergence-divergence regions or CDRegions in Chapter 6 and indicated that they are made of numerous convergence-divergence zones. CDRegions are strategically located within high-order association cortices but not within the image-making sensory cortices. They surface in sites such as the temporoparietal junction, the lateral and medial temporal cortices, the lateral parietal cortices, the lateral and medial frontal cortices, and the posteromedial cortices. These CDRegions hold records of previously acquired knowledge regarding the most diverse themes. The activation of any of these regions promotes the reconstruction, by means of divergence and retroactivation into image-making areas, of varied aspects of past knowledge, including those that pertain to one’s biography, as well as those that describe genetic, nonpersonal knowledge.

...One of the main CDRegions, the posteromedial cortices (PMCs), appears to have a higher functional hierarchy relative to the others and exhibits several anatomical and functional traits that distinguish it from the rest. A decade ago I suggested that the PMC region was linked to the self process, albeit not in the role I now envision. Evidence obtained in recent years suggests that the PMC region is indeed involved in consciousness, quite specifically in self-related processes, and has provided previously unavailable information regarding the neuroanatomy and physiology of the region. (The evidence is discussed in the last sections of this chapter.)

...The final candidate is a dark horse, a mysterious structure known as the claustrum, which is closely related to the CDRegions. The claustrum, which is
located between the insular cortex and the basal ganglia of each hemisphere, has
cortical connections that might potentially play a coordinating role. Francis Crick was convinced that the claustrum was a sort of director of sensory operations charged with binding disparate components of a multisensory percept. The evidence from experimental neuroanatomy does reveal connections to varied sensory regions, thus making the coordinating role quite plausible. Intriguingly, it has a robust projection to the important CDRegion that I mentioned earlier, the PMC. The discovery of this strong link occurred only after Crick’s death and was thus not included in the posthumously published article that he wrote with Christof Koch, in which he made his case.1

The problem with the claustrum’s candidacy as coordinator resides in its small scale when we consider the job that needs to be performed. On the other hand, given
that we should not expect any of the structures discussed earlier to perform the
coordinating job single-handedly, there is no reason why the claustrum should not make a relevant contribution to the construction of the autobiographical self. _Self Comes to Mind
Damasio also describes a number of other key brain structures -- including the brain stem -- in connection with their role in constructing a conscious self. The path to consciousness is serpentine, and feeds back upon itself in intricate ways.
Antonio Damasio


What is the point to this? Simply, if you want to understand the mind -- your own or someone else's -- there are a number of things which you will need to process almost simultaneously, at various levels of basic and emergent logic. You cannot do that without having done a great deal of reading, thinking, experiencing, observing, and experimenting. Fortunately for non-scientists, the entire human world is a great experimental laboratory for studying cognition.

Secondarily, if you want to create a machine consciousness, you may want to understand how the only proof of concept in the known universe -- the human brain -- manages to achieve the task at variable levels of competence.

Readings:

For an introduction to consciousness, Susan Blackmore's intro to the topic is one of the best places to start.

Antonio Damasio's book, Self Comes to Mind, is an interesting progression beyond an introductory review on consciousness.

At a somewhat deeper level, Gyorgy Buszaki's Rhythms of the Brain will connect many elements of neuronal structure and activity with higher levels of brain function.

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1 Comments:

Blogger Divine Potentate Lord Ossel said...

Rhythms was a great read, I'm rereading it at the moment. I'd also recommend the works of ray jackendoff, dealing with language and consciousness.

Sunday, 03 April, 2011  

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