What does it mean to “feel?” By what process do we gauge our emotions? In other words, how is it that we know we are angry, sad, hungry, fearful, tired, excited, etc.?
A brief examination of what is referred to by Drs. Craig, Critchley, Garfinkel, and others as “interoception” may provide some helpful insights into these questions.
Unlike the common five exteroceptive senses (sight, hearing, touch, smell, and taste), the vestibular system (movement), and the proprioception system (body awareness), interoception has been referred to as the eighth sensory system and encompasses the physiological process whereby we detect and can then respond to the ever-changing conditions within us. It also differs from proprioception (our ability to sense body position).
In his article “Interoception: The Eighth Sensory System,” neurologist Dr. Manuel Casanova explains the physiological basis for the interoceptive system:
The interoceptive system has specialized cells or receptors located throughout most of the tissues in the body, in your heart, lungs, stomach, bladder, genitals, muscles, skin, bones and so forth. These receptors gather information and send it to an area in the brain called the insula. The insula uses the incoming information to help you identify conditions like pain, hunger, fullness, itch, coldness, warmth, nausea, need for the bathroom, physical exertion, sexual arousal, anger, calmness, distraction or fear.
There is currently discussion among neuroscientists about the relationship between these physical indicators and emotional stimuli. Bechara and Naqvi summarized some of the discussion about this in an article published in Nature Neuroscience.
James and Lange suggested that feelings are the consequence of these body sensations, but philosophers have argued that the two differ because they have different objects. Body sensations involve awareness of the body's internal state; feelings are directed toward objects in the external world. Damasio has argued, however, that emotional feelings require the two objects—the body, which provides a substrate for feeling, and the external object that triggers the body changes in the first place, and toward which the feeling is directed.
Bechara and Naqvi go on to point out that it is the “neural patterns that represent changes in the body's response to an emotional stimulus” that help to produce what we experience as the emotion. They continue:
Critchley and colleagues now provide data suggesting that the subjective experience of emotions results from brain activity caused by such body states. Using functional magnetic resonance imaging (fMRI) and voxel-based morphometry (which estimates the size of a brain region), they identified brain areas engaged when subjects tried to sense whether their heartbeat was in sync with a series of tones. The size and activity of the right anterior insular cortex were related to individuals' accuracy in sensing the timing of their own heartbeats. Activity in this region was also correlated with an individual's propensity to subjectively experience certain emotions. These findings provide important validation of the theoretical view of James and Lange that neural systems supporting the perception of body states are a fundamental ingredient in the subjective experience of emotions.
Since emerging research appears to be validating the long-suspected theory that the process of interoception underlies our feelings and emotions, further practical knowledge in this area could eventually prove successful in diagnosing and treating any number of emotional disorders and behavioral difficulties. (For example, see Martin Paulus and Murray Stein’s article “Interoception in Anxiety and Depression.”)
One area this research is already beginning to help is in the understanding of self-regulation issues. To quote again from Dr. Manuel Casanova:
Clear internal information is essential for management of both body states like hunger, thirst and need for the bathroom as well as management of emotions like anxiety, anger. Specifically speaking, if you are able to notice and give meaning to internal signals it, in turn, alerts you that your internal balance is off and motivates us to take action — to do something that will restore the internal balance and help us feel more comfortable…On the contrary, if internal sensations are confusing, vague or absent, it can lead to a delayed or nonexistent urge for action.
While there is research beginning to indicate that mindfulness-based stress reduction (MBSR) methods may improve certain aspects of interoceptive awareness (e.g., see here and here), this is still a subject open to further exploration. For now, the prospects are exciting, but much more work needs to be done in this potentially ground-breaking field of research.