By David Brown
Washington Post Staff Writer
Monday, January 10, 2011; 10:20 PM
The single most important thing that will determine how much damage Rep. Gabrielle Giffords (D-Ariz.) suffered in Saturday's shooting is the precise path the bullet took through her brain - a detail not yet revealed by her physicians.
A general description of the wound and Giffords's condition suggests the bullet may have missed the language and vision regions of her brain. But it may have damaged a region responsible for controlling parts of the right side of her body, as well as areas involved in understanding sensations and planning movements.
Her long-term outcome, however, also depends on numerous other variables, some of which will be known soon and others not for months. They include whether the brain swells further and complications such as wound infection or pneumonia can be avoided, as well as the skill and duration of rehabilitative therapy and how hard the patient works at it.
"It's speculative and difficult to predict what will happen," said Michael R. Yochelson, medical director for brain injury programs at National Rehabilitation Hospital, in Washington. "More than in any other field of medicine the response to this kind of injury is so individualized."
Nevertheless, the brain is the most precisely organized organ in the body. Regions are responsible for specific actions, often very different ones even when the regions are near each other. The left side of the brain, where Giffords is injured, functions somewhat differently from the right. Bullets whose trajectories differ by a few degrees of an angle or are fractions of an inch apart can have profoundly different consequences.
As a result of this functional topography, it's possible to describe the general sort of disability that might result from a wound.
A back-to-front bullet track, as Giffords's appears to be, would have more devastating consequences the closer it is to the neck. A path near the top of the head would cause both less and different damage. Giffords's wound appears to be more like the latter than the former.
The evidence for that is her ability to respond to the spoken request to display a certain number of fingers. Many parts of the brain are involved in that task, but language comprehension resides mostly in what's known as Wernicke's area, which is part of the temporal lobe near the temple and ear.
The bullet appears to have passed above that area. It may have entered high enough to also miss the visual cortex, which ends about halfway up the back of the head. Asked whether Giffords's vision was impaired, her neurosurgeon at University Medical Center in Tucson, Michael Lemole, said it hadn't been tested but "the hope is that it won't be affected."
A trajectory going back to front at that level on the left side of the head would pass through through the parietal and frontal lobes, large regions involved in complicated mental actions.
The bullet would hit the left visual association area at the back of the head first. That region is responsible for determining the meaning of what one sees. Damage can result in so-called neglect syndromes in which a person is unaware of objects on one side. The person may fail to eat food on the right side of a plate, and in severe cases may not even recognize a right arm or leg as his or her own.
That region is also involved in comprehension of symbols, such as the numbers and hands on a clock. A person also may not be able to put in correct order a series of pictures, such as ones showing a full plate of cookies, a boy next to a half-empty plate and an empty plate.
Farther forward, the bullet would hit the somatic sensory cortex, which is responsible for comprehending touch. A person with damage there may not be able to identify that a quarter placed in the hand is a coin.
Forward of that is the motor cortex, which contains brain cells that control specific muscles. Which parts of the body - toes, leg, arm, finger, face - may be permanently weakened or paralyzed depends on exactly where the bullet passes. The left side of the brain controls the right side of the body, so any disability would be on the right.
Forward of that are areas responsible for planning complex movements, such as walking, and for controlling eye movements. Closest to the forehead is a section of the brain responsible for mood, self-control and creative thought.
Giffords is on a ventillator and sedated most of the time to minimize stress to her brain. The extent of her disabilities isn't known. But the fact she can follow directions is extremely encouraging, several experts said.
"Her prognosis for maintaining the function that she has is very good. It's over 50 percent," said Army Col. Geoffrey Ling, a neurological intensive care physician at the Uniformed Services University in Bethesda who flew to Tucson on Monday to consult on the case.