Pubdate: Tue, 06 Feb 2007
Source: New York Times (NY)
Copyright: 2007 The New York Times Company
Contact:  http://www.nytimes.com/
Details: http://www.mapinc.org/media/298
Author: Sandra Blakeslee

A SMALL PART OF THE BRAIN, AND ITS PROFOUND EFFECTS

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 give up 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 Dr. 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 a 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 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.

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.

Another neuroscientist, Arthur D. Craig at the Barrow Neurological 
Institute in Phoenix, went on to describe exactly the circuitry that 
connects the body to the insula.

According to Dr. Craig, the insula receives information from 
receptors in the skin and internal organs. Such receptors are nerve 
cells that specialize in different senses. Thus there are receptors 
that detect heat, cold, itch, pain, taste, hunger, thirst, muscle 
ache, visceral sensations and so-called air hunger, the need to 
breathe. The sense of touch and the sense of the body's position in 
space are routed to different brain regions, he said.

All mammals have insulas that read their body condition, Dr. Craig 
said. Information about the status of the body's tissues and organs 
is carried from the receptors along distinct spinal pathways, into 
the brain stem and up to the posterior insula in the higher brain or cortex.

As such, all mammals have emotions, defined as sensations that 
provoke motivations. If an animal is hot, it seeks shade. If hungry, 
it looks for food. If hurt, it licks the wound.

But animals are not thought to have subjective feelings in the way 
that humans do, Dr. Craig said. Humans, and to a lesser degree the 
great apes, have evolved two innovations to their insulas that take 
this system of reading body states to a new level.

One involves circuitry, the other a brand new type of brain cell.

In humans, information about the body's state takes a slightly 
different route inside the brain, picking up even more signals from 
the gut, the heart, the lungs and other internal organs. Then the 
human brain takes an extra step, Dr. Craig said. The information on 
bodily sensations is further routed to the front part of the insula, 
especially on the right side, which has undergone a huge expansion in 
humans and apes.

It is in the frontal insula, Dr. Craig said, that simple body states 
or sensations are recast as social emotions. A bad taste or smell is 
sensed in the frontal insula as disgust. A sensual touch from a loved 
one is transformed into delight.

The frontal insula is where people sense love and hate, gratitude and 
resentment, self-confidence and embarrassment, trust and distrust, 
empathy and contempt, approval and disdain, pride and humiliation, 
truthfulness and deception, atonement and guilt.

People who are better at reading these sensations -- a quickened 
heart beat, a flushed face, slow breathing -- score higher on 
psychological tests of empathy, researchers have found. The second 
major modification to the insula is a type of cell found in only 
humans, great apes, whales and possibly elephants, Dr. Allman said. 
Humans have by far the greatest number of these cells, which are 
called VENs, short for Von Economo neurons, named for the scientist 
who first described them in 1925. VENs are large cigar-shaped cells 
tapered at each end, and they are found exclusively in the frontal 
insula and anterior cingulate cortex.

Exactly what VENs are doing within this critical circuit is not yet 
known, Dr. Allman said. But they are in the catbird seat for turning 
feelings and emotions into actions and intentions.

The human insula, with its souped-up anatomy, is also important for 
processing events that have yet to happen, Dr. Paulus said. "When you 
decide to go outside on a cold day, your body gets ready before you 
hit the cold air," he said. "It starts pumping blood to where you 
need it and adjusts your metabolism. Your insula tells you what it 
will feel like before you step outside."

The same goes for drug addicts. When an addict is confronted with 
sights, sounds, smells, situations or other stimuli associated with 
drug use, the insula is activated before using the drug.

"If you give cocaine to an addict, you are affecting their brain's 
reward system, but this is not what drives the person to keep using 
cocaine," Dr. Paulus said. The craving is what gets people to use.

For example, smokers enjoy whole-body effects, said Nasir Naqvi, a 
student at the University of Iowa Medical Scientist Training Program, 
who was the lead author of the recent article on smoking. It is not 
just nicotine binding to parts of the brain, he said, but sensations 
- -- heart rate, blood pressure, a tickle in the lungs, a taste in the 
mouth, the position of the hands, all the rituals.

The insula's importance makes it an ideal target for many kinds of 
treatment, Dr. Paulus said, including drugs and sophisticated 
biofeedback. But methods to quell insular activity must be approached 
carefully, he said. People might lose the craving to smoke, drink 
alcohol or take other drugs, but they could simultaneously lose 
interest in sex, food and work.

As clinicians explore the possibilities, Dr. Craig is thinking about 
the insula in grander terms.

For example, lesions in the frontal insula can wipe out the ability 
to appreciate the emotional content of music. It may also be involved 
in the human sense of the progress of time, since it can create an 
anticipatory signal of how people may feel as opposed to how they 
feel now. Intensely emotional moments can affect our sense of time. 
It may stand still, and that may be happening in the insula, a 
crossroads of time and desire.
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MAP posted-by: Beth Wehrman