The recent news about smoking was sensational: some people with damage to a prune-size slab of brain tissue called the insula were able to quit cigarettes instantly.
Suppose scientists could figure out how to tweak the insula without damaging it. They might be able to create that famed and elusive free lunch — an effortless way to kick the cigarette habit.
That dream, which may not be too far off, puts the insula in the spotlight. What is the insula and how could it possibly exert such profound effects on human behavior?
According to neuroscientists who study it, the insula is a long-neglected brain region that has emerged as crucial to understanding what it feels like to be human.
They say it is the wellspring of social emotions, things like lust and disgust, pride and humiliation, guilt and atonement. It helps give rise to moral intuition, empathy and the capacity to respond emotionally to music.
Its anatomy and evolution shed light on the profound differences between humans and other animals.
The insula also reads body states like hunger and craving and helps push people into reaching for the next sandwich, cigarette or line of cocaine. So insula research offers new ways to think about treating drug addiction, alcoholism, anxiety and eating disorders.
Of course, so much about the brain remains to be discovered that the insula's role may be a minor character in the play of the human mind. It is just now coming on stage.
The activity of the insula in so many areas is something of a puzzle. "People have had a hard time conceptualizing what the insula does," said Martin Paulus, a psychiatrist at the University of California, San Diego.
If it does everything, what exactly is it that it does?
For example, the insula "lights up" in brain scans when people crave drugs, feel pain, anticipate pain, empathize with others, listen to jokes, see disgust on someone's face, are shunned in social settings, listen to music, decide not to buy an item, see someone cheat and decide to punish them, and determine degrees of preference while eating chocolate.
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 Paulus and others, is that mind and body are integrated in the insula. It provides unprecedented insight into the anatomy of human emotions.
The brain's netherworld
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.
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