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Anxiety and the Insular Cortex: A Budding Relationship

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Sunday, 18 October 2009

I wrote an article not too awful long ago that summarized a bit of research by Dr. Jack Nitschke of the University of Wisconsin-Madison. Dr. Nitschke's work focused upon the role of the element of uncertainty in intensifying reactions to disturbing events, as well as increasing overall levels of anxiety. Nitschke noted a piece of brain anatomy known as the insular cortex. I didn't know much about it, so I did some digging. And here's what I found.

The insular cortex (a.k.a. insula, insulary cortex) is a mass of neurons that lie in the midst of the temporal, parietal, and frontal lobes. Even though there are actually two insula, as they're contained in both brain hemispheres, I'll be using the term "insula," in the singular. Incidentally, the word "insula" comes from the Latin for island.

Now, some authorities view the insula as a lobe of its own, and others see it as part of the temporal lobe. Yet others, who assign it to the limbic system, consider the insula and the other components of the limbic system, a separate limbic lobe. The insula is divided into two parts, an anterior and smaller posterior section. As you read this article, always remember the insula is all about subjective human experience. Indeed, it's been said the insula is responsible for what it feels like to be human, as opposed to just another mammal.

To say the very least, the insula is very well connected. It receives input from the brain's great sensory hub, the thalamus; as well as from the very headquarters of our fear and emotion circuitry, the amygdala. And the communication with the amygdala is actually two-way. There's also a bilateral line of communication with the primary sensory cortex. Given these landmarks it's obvious the insula is deeply involved with a wide variety of functioning linked to emotion and the maintenance of homeostasis, our body's ability to maintain a relatively stable state of internal regulation and equilibrium. And, yes, it's a frequent contributor to assorted psychopathology, particularly anxiety. Hey, I find it terribly interesting that scans have shown the right anterior insula is significantly thicker in people who meditate.

Well, since the insula is involved in such a wide variety of sensation and functioning, we're going to take a look at things categorically. And though the information is certainly available, I'm going to consider the insula's functioning as a whole, rather than specifying the anterior and posterior sections. One last note. The insula is very much in the mix with regard to motor control and, as I cited, homeostatis. However, I won't be going into detail on either.

Interoception
Interoception is the sensing of stimuli arising from within our bodies, especially from the major organs of the trunk. A great example is the ability to time your own heartbeat. The insula is also activated upon physical exertion and becomes involved with blood pressure control, especially after exercise. Other interoceptive dynamics involving the insula are: perceived intensity of pain, how we imagine pain would feel in our own bodies when we observe images of painful events involving others, the degree of the skin's non-painful warmth or coldness, sensations of a distended stomach and full bladder, loss of balance, vertigo, and the sensations involved with passive listening to music, laughter, crying, and language.

Emotion
The insula is receiving more and more attention as it applies to its role in body representation and subjective emotional experience (e.g.: feelings). The insula is thought to process a convergence of stimuli, formulating an emotionally relevant context for all the hub-bub. It's also very much involved in sensing feelings of anger, fear, disgust, happiness, and sadness. And let's not forget about conscious desires such as food and drug craving. Absolutely, the insula is a player in addiction and addictive behavior. Just one example is the insula's ability to read body states like hunger and craving; ultimately pushing people to reach for that second sandwich, cigarette, or line of cocaine.

Believe me, giving the insula its due would require a book. And that's why I had to make this particular presentation short and to the point. But, go ahead, do some research. No doubt, the insula is a fascinating and still mysterious accumulation of neurons. However, as I said earlier, it's receiving more and more attention. I liken it to the development of interest in the amygdala. It actually began in earnest in the 1930's, and with the invention and development of imaging instruments and techniques, the research continued. Of course, now we know the amygdala as the epicenter of our emotions and fears. And having this knowledge at hand opens all sorts of doors for creative and effective relief and curative measures for, as it applies to us, panic and anxiety.

So here's to tomorrow and the insular cortex. I'm thinking bunches of great news is just around the corner.

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