Friday, June 18, 2010

Pardon Me, Madame: Is That My Arm Up Your Dress?

How odd that Charlie would not know that it is his arm up Mrs. Randthorpe-Fitzgerald's dress. But we all remember that Charlie suffered an infarction of his right insular cortex following a stroke last spring. Yes, of course, Charlie must be suffering from left sided neglect -- he doesn't know that his left arm is actually his.

But wait a minute! It is Charlie's right arm that is up Mrs. R-F's dress. Charlie, you dog! And why is Mrs. R-F smiling?
This is where the insula is located -- hidden beneath the temporal lobe (cut away in the illustration). It is like an island into itself, and is in many ways like a separate brain. But the insula happens to be crucial to a person's sense of self, and to his consciousness. Here is how:
The insula has increasingly become the focus of attention for its role in body representation and subjective emotional experience. In particular, Antonio Damasio has proposed that this region plays a role in mapping visceral states that are associated with emotional experience, giving rise to conscious feelings. This is in essence a neurobiological formulation of the ideas of William James, who first proposed that subjective emotional experience (i.e. feelings) arise from our brain's interpretation of bodily states that are elicited by emotional events. This is an example of embodied cognition.
Functionally speaking, the insula is believed to process convergent information to produce an emotionally relevant context for sensory experience. More specifically, the anterior insula is related more to olfactory, gustatory, vicero-autonomic, and limbic function, while the posterior insula is related more to auditory-somesthetic-skeletomotor function. Functional imaging experiments have revealed that the insula has an important role in pain experience and the experience of a number of basic emotions, including anger, fear, disgust, happiness and sadness.
Functional imaging studies have also implicated the insula in conscious desires, such as food craving and drug craving. What is common to all of these emotional states is that they each change the body in some way and are associated with highly salient subjective qualities. The insula is well situated for the integration of information relating to bodily states into higher-order cognitive and emotional processes. The insula receives information from "homeostatic afferent" sensory pathways via the thalamus and sends output to a number of other limbic-related structures, such as the amygdala, the ventral striatum and the orbitofrontal cortex, as well as to motor cortices. [45]

A study using magnetic resonance imaging has found that the right anterior insula was significantly thicker in people whomeditate[46]

It is remarkable to think that such a small, hidden patch of cortex could be so pivotal to the "soul" of each human being. Al Fin has long championed the concept of "Embodied Cognition", the idea that a mind must have a body in order to be functionally conscious. Particularly when one's consciousness rests so crucially upon a sense of self.

The insula is also thought to be important in the act of decision-making including, perhaps, the making of moral decisions. That makes sense, given the importance of the insula to one's internal body sense, or "gut sense."

Many of our decisions are based upon gut instincts, as it were. Some acts and people "make us sick", while others leave us weak, strong, or make our heads hurt. The way our bodies feel about things can influence us far more than we realise.

And so we leave the insulae of one armed Charlie and Mrs. R-F in the parlour, performing an ancient "dance of the insular cortices."

Meanwhile we may contemplate how it would be possible to insert an insula-like processor into a machine brain, to give it a sense of embodiment. It would be but a bare beginning, of course. But it would be a rational beginning.

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