Their views came after Rep. Gabrielle Giffords, D-Ariz., was shot in the head and severely injured during a shooting spree in Arizona that killed 6 people.

“I have seen every foreign body in the world pass through the brain, and I never cease to be amazed that some seem to survive and do amazingly well,” said Dr. Ian Armstrong, who is now on the staff at Cedars-Sinai Medical Center in Los Angeles but was a trauma neurosurgeon at Texas Medical Center at a time when it had the highest rate of penetrating head trauma in the country.

A bullet to the brain “for us, is almost a weekend occurrence, and some of them survive,” said Dr. Rafael Quinonez, a trauma neurosurgeon at Providence Holy Cross Medical Center in Mission Hills.

The most crucial factor in a brain injury is which part of the brain is hit. The worst area is the brain stem, which is critical to control of breathing and other bodily functions. A bullet that passes through the brain stem is typically immediately lethal.

Next most serious would be if the bullet passes through both hemispheres of the brain, striking the diencephalon, which connects the two hemispheres and which is the critical area for a number of functions, such as consciousness and awareness. That is usually also fatal.

Media reports indicate that Giffords, is responding to commands from her doctors following surgery. If the bullet had gone through that area, “she would not be following commands,” said Dr. Neil A. Martin, chair of Neurosurgery at UCLA’s Reagan Medical Center. “That’s a very favorable finding.”

The bullet, according to the doctors treating her, passed through the head and back out. Experts said that was fortunate because surgeons didn’t have to dig it out and it didn’t break up into smaller pieces that could do more damage.

There are other areas of the brain, he noted, called “eloquent areas,” where damage can cause significant neurological deficits, such as problems moving arms or legs, speech problems or the like.

President Ronald Reagan’s press secretary James Brady, for example, suffered such damage when he was shot in the head during the assassination attempt on Reagan. If those regions were spared, Giffords could have a significant recovery.

Quinonez noted that, a couple of years ago, he treated a Palmdale carpenter who accidentally embedded six nails in his brain with a nail gun because those regions were spared.

Assuming the damage to the congresswoman’s brain is minimal, there are still many potential complications her physicians will have to watch out for, Martin said, such as infections and brain swelling.

Surgeons might, for example, have to remove some bone to allow the brain to enlarge a little bit if swelling occurs.

Vasospasm, a reaction of the blood vessels in the brain to the shock wave of the bullet and the subsequent bleeding, could occur as long as a week later, causing the vessels to contract and leading to a stroke.

Also, any injury to the brain could lead to a seizure, Martin said, so they will put her on medication to prevent them. “Her future looks reasonably promising, but there is a lot to watch for over the next week.”