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By SANDRA BLAKESLEE

Published: August 2, 2005

Dr. Anna Berti sits facing a patient whose paralyzed left arm rests in her lap next to her good right arm. "Can you raise your left arm?" Dr. Berti asks.

"Yes," the patient says.

The arm remains motionless. Dr. Berti tries again. "Are you raising your left arm?" she asks.

"Yes," the patient says. But the arm still does not move.

Dr. Berti, a neuroscientist at University of Turin in Italy, has had many such conversations with stroke patients who suffer from denial syndrome, a strange disorder in which paralyzed patients vehemently insist that they are not paralyzed.

This denial, Dr. Berti said, was long thought to be purely a psychological problem. "It was a reaction to a stroke: I am paralyzed, it is so horrible, I will deny it," she said.

But in a new study, Dr. Berti and her colleagues have shown that denial is not a problem of the mind. Rather, it is a neurological condition that occurs when specific brain regions are knocked out by a stroke.

Patients deny the paralysis because a closely related region of the brain that is still intact appears to tell them that their bodies are responding normally.

The study, published in the July 15 issue of Science, may also shed new light on the nature of consciousness. Self-awareness, the researchers say, is not located in a unique brain structure or mechanism, but instead is distributed in many parts of the brain. As a result, there are different kinds of awareness for functions like movement, vision, awareness of the body and the space around the body.

Dr. Christof Koch, a neuroscientist and expert on consciousness at the California Institute of Technology in Pasadena, said the research was also interesting because it helped answer a fundamental question, namely, "What gives me the feeling that I know I am moving my hand or feel that I move my hand?"

Denial, Dr. Berti said, is usually considered to be a subfeature of a more common neurological syndrome called neglect. In neglect, patients suffer a stroke in the right side of the brain that results in paralysis of the left side of the body. Damage is pronounced in a region toward the back of the brain where personal space around the body is literally mapped and encoded by cells.

Neglect patients ignore everything, including their paralyzed limbs, in the left side of space, Dr. Berti said. But if their attention is purposefully drawn to that space, they recognize that their arm is paralyzed. They do not deny their situation.

But because denial and neglect can occur independently, Dr. Berti said she decided to see if patients who exhibited denial showed different underlying brain pathology.

For the study, 30 stroke patients underwent anatomical brain scans to pinpoint the source of their brain damage. All were paralyzed on the left side. Twelve patients exhibited neglect. Another 17 showed neglect and denial. One patient displayed only denial.

By comparing brain images, the researchers hoped to subtract denial from neglect, to see where the disorder resides in brain circuitry. As expected, neglect frequently involved damage to a region toward the back of the brain called the parietal lobe, as well as to nearby structures. Damage was also seen below the brain's mantle, or cortex, in tissue called white matter.

But to the researchers' surprise, brain damage in the patients who displayed denial tended to occur in the front part of the brain, particularly in the circuits that control movements and the planning of movements and in a region that helps produce feelings about the body.

Dr. Berti said these regions appeared to work together to generate, plan and perceive actions. They also generate self-awareness of actions.

Denial seems to arise from the fact that in patients who display the disorder, a related brain area is less affected or unaffected, Dr. Berti said. Called the supplementary motor area, it is involved in the mental simulation of movements. When athletes close their eyes and imagine a golf swing or skiing motion, this part of the brain is activated.

When patients who display denial are asked to raise an arm or clap their hands, the region that imagines these movements produces a familiar pattern of brain activation, showing normal or close to normal function, Dr. Berti said.

But the regions that maintain awareness of movements and carry them out are not working. The conflict between these regions, she said, becomes overwhelming.

The sense of having moved is powerful but awareness is absent. The solution for the paralyzed patient is to confabulate. If prodded for hours, patients will make up stories to explain their lack of action, Dr. Berti said.

One man said his motionless arm did not belong to him. When it was placed in his right visual field, he insisted it was not his.

"Whose arm is it?" Dr. Berti asked.

"Yours," he said.

"Are you sure?" Dr. Berti persisted. "Look here, I only have two hands."

The patient replied: "What can I say? You have three wrists. You should have three hands."

http://www.nytimes.com/2005/08/02/science/02deni.html?ex=1124164800&en=86ee7ef49dcd3325&ei=5070