Friday, March 09, 2007

Disconnecting the brain from the body: Anosognosia

Mrs. M. is adamant. People are saying her left side is paralyzed, and she knows they are wrong. Several days ago the 76-year-old Californian suffered a stroke. She now sits in a wheelchair while a doctor in a crisp cream-colored suit bends over her, asking questions. She answers them with perfect coherence. Does she know where she is? Yes, she is in a hospital, brought here by her daughter. Does she know what day of the week it is? Of course. It is Tuesday afternoon.

Then the doctor starts in again about her hands. Can she use her right hand? Yes. Her left? Yes, of course. He asks her to use her right hand to point to a student who is taking notes, and she obliges. He asks her to point to the student with her left hand instead. This time she doesn’t move.

Mrs. M., why didn’t you point? asks the doctor. For the first time, she hesitates.

Because I didn’t want to, she answers.

In fact, fibers in the motor cortex on the right side of her brain, which controls movement on her left side, have been irreparably damaged by the stroke, and she will never use her left arm again. But Mrs. M. is not a stubborn old woman refusing to admit a difficult truth. A few minutes later Mrs. M. looks at her left hand, resting inertly in her lap.

Doctor, she asks, whose hand is this?

Whose hand do you think it is?

Well, it certainly isn’t mine!

Then whose is it?

It is my son’s hand, Doctor.

Mrs. M.’s claim would be peculiar enough if her son were in the room, but he is miles away, unaware that in his mother’s mind his hand has become attached to her arm. Mrs. M. is suffering from a condition called anosognosia, which sometimes appears when a stroke has cut off blood being supplied to the brain through the middle cerebral artery. The stroke damages regions in the brain’s right hemisphere that include a territory called the right parietal cortex, a patch of neurons about two-thirds of the way back along the brain. The two parietal cortices (there is one in the left hemisphere also) are known to be involved in directing the brain’s attention to movements, objects, and sensations on the opposite side of the body, as well as in the perception of that entire side of the body in space.

While otherwise clearheaded, patients with damage to the right parietal cortex are unable--not just unwilling--to acknowledge the radical change that has overcome the left side of their body. (The term anosognosia derives from nosos and gnosis, the Greek words for disease and knowledge.) One of the best-known victims of the condition was Supreme Court justice William O. Douglas, who suffered a right-hemisphere stroke in 1974 that paralyzed his left side and eventually forced his retirement. He initially dismissed the paralysis as a myth, and weeks later he was still inviting reporters to go on hiking expeditions with him. When one visitor asked about his left leg, he claimed that he had recently been kicking 40- yard field goals with it in the exercise room and soon planned to try out for the Washington Redskins.

Mrs. M.’s form of anosognosia is even more extreme: she not only flatly denies she is paralyzed, she refuses to admit that the limp limb on the left has anything at all to do with her. One such anosognosiac became so incensed that somebody else’s leg was cluttering up his hospital bed that he heaved the thing out and was subsequently amazed to find himself on the floor. Another claimed that the arm on the left belonged to his daughter, who was trying to seduce him.

We are used to thinking of our bodies as our selves, says Vilayanur Ramachandran--the inquisitive doctor in the cream-colored suit. Something has gone wrong here that calls that fundamental truth into question.....................Whole article here.


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