Consciousness 1: The neural correlates of consciousness (neurological perspective) (v1.0)

This is the highlight of an article from the economist that I thought was interesting. 

The greatest question posed in science is what is consciousness? "I think, therefore I am." Rene Descartes’ aphorism has become a cliche. As Descartes observation suggests, a conscious being knows he/she is conscious. But he cannot know that any other being is. Consciousness is subjective. Other apparently conscious individuals might be zombies programmed to behave as if they were conscious, without actually being so (though for other humans it is farfetched to believe so). It gets even muddier with other species. Are chimpanzees conscious? Dogs? Codfish? Bees? It is hard to know how to ask them in a meaningful way.

Blindsight is an interesting neurological disorder - it happens when blindness is caused due to certain damage to visual cortex in the brain. Those who have blindsight have no conscious awareness of being able to see. They are nevertheless able to point to, and even grasp, objects in their visual field. This illustrates how apparently conscious actions can occur without consciousness. 

There are many dimensions to a study of consciousness in humans (like evolutionary perspective, neurological perspective, philosophical perspective, and psychological perspective). Here I will focus on only neurological aspects. The views here are not harmonized with views from other dimensions. 

There has been a search for the neural correlates of consciousness. A person could suffer the loss of the cerebellum or large bilateral portions of the medial temporal lobes, including amygdala and hippocampus complex, and would not become unconscious. This points to specific areas related to consciousness. Cortical lesions for example can result in such specific impairments of consciousness where one may no longer be able to speak, perceive color, or identify parts of themselves as their own. 

One potential neural correlates of particular interest are claustrum (one in each hemisphere). In 2003, Crick (father of DNA) and Koch formed a hypothesis about the central role of Claustrum in consciousness. The claustrum has extensive connections to other parts of the brain. The pair are thin sheets of nerve cells tucked below the cerebral cortex that have connections both to and from almost every area of the cortex. They are the only structures that link the various parts of the cortex in this way. A crucial property of consciousness is that it integrates many sorts of experiences, both sensory and internally generated. In 2005 a paper looked at this problem. They suggested they act like orchestral conductors, coordinating the activities of the cortical components and thus solving the integration problem. In 2014 Mohamad Koubeissi, an American neurologist while studying a epilepsy patent, put an electrode near a claustrum. When the switch was turned on, the patient lost consciousness. When turned off, consciousness returned. He got the same results when tried multiple times. A relatively recent paper suggests more specifically how claustrum may be involved in consciousness in the temporal arena: Claustrum, consciousness, and time perception - ScienceDirect 

Another clue is gamma waves. Gamma waves (electrical impulses at 40HZ that beat in synchrony in different parts of the brain) is strongest during conscious concentration on tasks, and always present when conscious, but largely disappear when asleep unless the person is dreaming. Many neuroscientists suspect gamma wave synchrony means they are acting like the clock in a computer processor, coordinating the activities of different parts of the brain.

Yet another potential neural correlate is temporoparietal junction (one in each hemisphere). The brain consists of multiple lobes including the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe. The place where the temporal and parietal lobes come together is called the temporoparietal junction. Damage to this part of the brain (or turning it off temporarily with transcranial magnetic stimulation - TMS) creates strange effects that include out of body experiences in which a person's conscious perception of himself appears (from his point of view) to detach itself from his body. It also reduces one's ability to empathize with the mental state of others. That suggests this part of the brain helps generate "theory of mind" - the ability to recognize that other creatures too, have minds. Since the only model available to a mind that wishes to understand another’s is itself, a theory of mind necessarily requires self-awareness. Human babies are able to do so from 18 months on. 

Finding the neural correlates of consciousness, or even understanding what it is for and how it evolved may eventually get resolved but does not truly address the question of what it actually is— what is it people are experiencing while they are conscious. This question has come to be known as the “hard problem” of consciousness (so dubbed in 1995 by David Chalmers, an Australian philosopher). It is both hard to resolve and at the same time its resolution is the heart of the matter. This really hard problem of consciousness is the problem of experience. When we think and perceive, there is a whir of information-processing, but there is also a subjective aspect. As Nagel (1974) has put it, there is something "it is like" to be a conscious organism. Here is Chalmers paper: Microsoft Word - facing.doc (consc.net)