The September edition of Scientific American Mind features an excerpted chapter that has definitely sharpened my appetite for the book. The Blakeslees discuss the point that this region is found only in primates and by extension, us. Frogs, even other mammals like dogs etc, even though they can act sometimes as if they can feel everything the way we do, can't/don't. But first they explain the system. Here is a small part of it:
Just as a road atlas is full of maps that represent real-world locations, your brain is full of body maps that represent aspects of yourself, inside and out. In contrast, the main goal of exteroception, externally oriented perception, is to create maps and models of your body, the world around your body, and your body's relation to the world. Your brain creates and maintains maps of your skin surface, limb position, joint movement and musculoskeletal system so that you can move about and interact with objects and people. You have distinct fibres in your spinal cord that carry such information in both directions: up from your body to your sensory maps and back down from your motor maps to your muscles.
Interoception is a separate realm of somatic sensation that is oriented inward. It has two sources. The first is the internally mapped state of your body. Bring your attention to the sensation these maps are generating in you right at the moment. Think about your heart, lungs, stomach, intestines, rectum, larynx, throat. Try to feel their activity if you can. All your innards have receptors that send information up to your brain for mapping your "gut" feelings of hunger, thirst, air hunger and other visceral sensations.
The second source of your interoceptive maps consists of a different class of receptors found on your body's surface, including your teeth, gums and tongue. Unlike the touch receptors that deal in pressure and vibration and are tied mainly to deliberate touch and action, these other receptors carry information about the "homeostatic" condition of your body - temperature, pain, itch, muscle ache, sexual arousal, crude touch and sensual touch. Homeostasis refers to your body's ability to maintain internal balance. Your spinal cord contains an evolutionary older set of fibres that carries this information to and from your brain.
This may seem strange at first, because many of your body parts end up being mapped by both systems. If someone pinches your arm, the pressure and pain will be represented in your primary touch map. But the pain will be rerepresented in your insula. Why is pain from one pinch mapped in two places? Because your insular maps serve a different function from your primary touch and motor maps. They are the command center for homeostatic self-regulation. For example, to run your body's thermostat properly - to keep your body temperature constant - your brain needs to know not just about your core temperature, but also about air touching your skin. Pain in your muscles, lungs and joints is important for marshaling your body's resources during exertion, but so are sensations of strain and movement and resistance in your joints and skin. So the primary brain maps for homeostatic signals from your body surface - about itch, sharp pain, dull pain, burning pain, tickle, sensual touch, heat and cold - as well as the sensations arising from your body's interior, are mapped in your insula, not in your primary touch cortex. You use those feelings less to deal with the outside world than to seek balance within your body and put your internal sensations in context. And as Critchley's results imply, interoception does far more for you than just letting you know your are hungry or exhausted or sexually sated. It is also a crucial ingredient in some of the most important aspects of human beingness: sentiment, sentience and emotional awareness.
The take home point here, is, keep your handling of patients, above all, kind.
Let kindness and slowness and non-invasiveness and invitation to move be the first and the main kinesthetic food you feed your patients' insulae, and all will be well.
This is the part of the brain you really need to impress with what a wonderful manual therapist you are, by being kinesthetically non-noceboic. Because it picks up emotional content so easily, make darn sure you are operating from your own best/highest emotional ground - THIS is the part of your patient's brain that can read your intention, emotionally. Give it NO reason to be suspicious of you in any way whatsoever. Make sure you get to know your own insula intimately, and inspect and repair the fence you put up around it, daily. These are your personal boundaries. In no way should your patient ever come to know what its contents are. What's in your own insula is absolutely none of their business.
"A memory is a moment when the past meets the future in the present" - Joseph LeDoux