Damage to the insula can lead to apathy, loss of libido and an inability to tell fresh food from rotten.

The bottom line, according to Dr. Paulus and others, is that mind and body are integrated in the insula. It provides unprecedented insight into the anatomy of human emotions.

Of course, like every important brain structure, the insula — there are actually two, one on each side of the brain — does not act alone. It is part of multiple circuits.

The insula itself is a sort of receiving zone that reads the physiological state of the entire body and then generates subjective feelings that can bring about actions, like eating, that keep the body in a state of internal balance. Information from the insula is relayed to other brain structures that appear to be involved in decision making, especially the anterior cingulate and prefrontal cortices.

The insula was long ignored for two reasons, researchers said. First, because it is folded and tucked deep within the brain, scientists could not probe it with shallow electrodes. It took the invention of brain imaging techniques, such as functional magnetic resonance imaging, or fMRI, to watch it in action.

Second, the insula was “assigned to the brain’s netherworld,” said John Allman, a neuroscientist at the California Institute of Technology. It was mistakenly defined as a primitive part of the brain involved only in functions like eating and sex. Ambitious scientists studied higher, more rational parts of the brain, he said.

Image Credit... Lou Beach

The insula emerged from darkness a decade ago when Antonio Damasio, a neuroscientist now at the University of Southern California, developed the so-called somatic marker hypothesis, the idea that rational thinking cannot be separated from feelings and emotions. The insula, he said, plays a starring role.