Interoception and nociception

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Chapter 10 endnote 19, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

The prominent neuroanatomist A. D. (Bud) Craig, who knows more about this circuitry than just about anyone else, argues that nociception is a form of interoception...

The Nobel laureate British neurophysiologist Charles Sherrington created a typology of sensations based on experience. He distinguished sensory inputs that relate to the world outside the body (exteroception) and sensory inputs that relate to the world inside the core of the body (interoception). Exteroception was divided into vision and hearing (teloreception), vs. taste and smell (chemorception). In exteroception, Sherrington also included sensory inputs that relate to limb position in space (proprioception), temperature (thermoreception), sensations deriving from touch (the somatosensory system), and sensory inputs that come from tissue damage, or threat of damage (nociception). Textbooks in anatomy and physiology continue to do the same.

Bud Craig revised the definition of interoception, based on anatomy, as all the sensations that represent the information carried by a set of neurons that are small in diameter and that run throughout the entire body (not only from the internal organs or viscera, but also from muscles, joints, teeth and skin). Craig argues that the skin, as an organ of the body, is important for keeping your body budget in balance (for example, the skin plays a crucial role in temperature regulation, hydration, and electrolyte balance which is important for your neurons to fire normally), and therefore classifies some somatosensory sensations as interoception.[1] Ditto for nociception. All interoceptive sensory inputs (nociception included) moves from the body (skin, muscle, and even bone) to the brain via neurons whose axons are small in diameters and that are either unmyelinated or lightly myelinated (meaning that the signal will move slowly along each axon, but signals from different neurons can influence one another as their signals move along the axons themselves and not just at the synapses[2]); this information is important for guiding ongoing changes in blood flow, respiration, metabolism, and so on. These small diameter neurons are follow a different path in the spinal cord than the large diameter neurons that guide the movements of the muscles attached to your skeleton to move your limbs (large diameter neurons signal skin contact with external stimuli, such as pressure, velocity, stretch, and frequency of vibration, as well as info from joints and muscles about force, position, etc). These two neural pathways are anatomically, genetically and embryologically distinct.

Primary nociceptive cortex (the dorsal, posterior part of the insula) is physically in the same bit of cortex as primary interoceptive cortex. The regions of the brain that control body-budgeting (and therefore interoception) via predictions are very likely the same as that modulate nociception.

Notes on the Notes

  1. Craig, A. D. 2015. How Do You Feel? An Interoceptive Moment with Your Neurobiological Self. Princeton, NJ: Princeton University Press.
  2. Damasio, Antonio, and Gil B. Carvalho. 2013. “The Nature of Feelings: Evolutionary and Neurobiological Origins.” Nature Reviews Neuroscience 14 (2): 143–152.