I recently attended the Wisconsin Symposium on Emotion (Now in its 14th year). Its topic was "Emotion, Consciousness and Psychopathology." I want to mention the talk given by A.D.(Bud) Craig, which was a real tour de force, the kind of science I feel I can integrate with my own personal experience. Its title was "How do you feel? The neurobiological basis for human awareness of feelings from the body." I have referenced Craig's work in previous posts, also check here. Here are PDFs of his two recent review articles in Trends in Cognitive Science (2005) and Nature Reviews Neuroscience (2002) which I recommend.
His view is that in our nervous systems, there is a fundamental bilateral partitioning or separation, from basic spinal cord and brain stem homeostatic systems to our highest prefrontal lobe functions, in which the right side spends energy and the left side brings it in. This reflects the relative activities of the sympathetic versus parasympathetic nervous systems. (enter 'parasympathetic' in the google search box in the left column to see some previous mindblog posts on autonomic regulation of chilling out versus getting excited).
The right and left insula appear to be central in processing feelings, all the way from basic (interoceptive) body sensing (posterior insula) up through subjective feelings, disgust, trust, anger, social hurt, empathic happiness, lust, pain, etc. All of these are homeostatic emotional currency that help regular body balance all the way from from blood pressure, glucose, heart rate, salt regulation, up through social self image. Here is a graphic from his 2005 article that shows the central role of the left and right anterior insula (which act as the sensory cortex of limbic system) in receiving information about body state and feeling from sympathetic and parasympathetic input and then interacting with anterior cingulate (the motor cortex of the limbic system) and frontal cortex. (click to enlarge):
Positive emotions (pleasant music, maternal emotions) correlate with enhanced left parasympathic, left anterior insula, left anterior cingulate and left frontal activation, while negative emotions (anger, fear, etc.) enhance activation of the corresponding structures on the right side.
Some very simple manipulations can stroke the relative activation of these two systems. Slowing one's breathing, as usually happens during meditation dials up the left anterior insula system, while breathing more rapidly increases anxiety and right anterior insula activity. In fact, giving instruction to a subject to breathe more slowly or more rapidly can change their emotional reaction to stimuli. In one experiment mentioned by Craig, a picture of a baby seal elicited warm nuturing emotions when breathing was slowed, but when breathing was increased, subjects were more likely to suspect the seal might attack or bite them! Experiments are now being attempted to measure whether oxytocin (the affiliative, trusting hormone) correlate with left insular activation while right insula activation correlates with cortisone (the stress hormone) release.
This sort of global description fascinates me, because it instructs us in how integrated a package we are, and how attention to some of the basement details of our daily life (such as breathing) can fundamentally alter our mood and temperament.