Recovery from brain trauma is likely to be a lifelong process for Gabrielle Giffords.Susan Walsh/AP Photo

Congresswoman Gabrielle Giffords (Democrat, Arizona) is resting in a medically induced coma. But her brain is undergoing a frenzy of activity in an attempt to heal itself from the trauma she suffered on Saturday, when she was shot in the head in Tucson, Arizona, by a gunman who also shot 19 other people, killing 6. Although Giffords's recovery could take years, it is possible that she could one day return to politics, doctors say.

"Do I think she could return to work as a Congresswoman? Yes," said Arthur Kobrine, a neurosurgeon in Washington DC who treated Jim Brady, the White House press secretary who was shot in the head in 1981 during an assassination attempt on US President Ronald Reagan. "But possible isn't the same as likely," says Kobrine.

Lifelong consequences of a brain injury are triggered by a cascade of neurochemical events in the seconds and minutes after the injury occurs, say Kobrine and other doctors and neuroscientists.

A bullet first destroys tissue that lies in its path, which for Giffords was on the left side of the brain. But it also damages neurons that don't lie directly in its path, because it is trailed by a pressure wave that transfers the energy of the bullet into the surrounding brain tissue.

This pressure wave activates all the neurons through which it passes. The neurons then attempt to restore their resting electrochemical balance by absorbing water, resulting in brain swelling. The restoration also takes an enormous amount of energy — more than the injured brain can provide — and so creates an 'energy crisis', or energy deficit in the brain.

Giffords's doctors are addressing these complications by removing a portion of her skull to relieve the pressure of her swelling brain, and by inducing a medical coma to reduce the brain's energy demands.

Fast and slow recovery

As the brain recovers from the exhaustion of the initial injury over weeks and months, patients recover some of their brain function in regions of the brain that weren't directly damaged by the injury. Gregory O'Shanick, chairman and past national medical director of the Brain Injury Association of America in Vienna, Virginia, says that patients recover some skills rapidly in the six months that follow an injury, but subsequently recover more slowly.

Some of the recovery is attributable to rewiring of the brain. Neurons that did not die during the injury sprout new connections, attempting to regain their functions and take over functions that may have been lost by neurons that did die. Patients also learn to compensate for lost abilities — for instance, by brushing their teeth with their left hands if they can no longer do so with their right.

And David Hovda, director of the Brain Injury Research Center at the University of California, Los Angeles, says that in the past few decades, neuroscientists have found evidence that the brain can grow new neurons, especially after a brain injury. "But whether they contribute to recovering function or reducing the size of deficits we don't know," says Hovda.

Giffords could regain much of her normal function through rehabilitative therapy, say doctors. Brady's story is instructive; he initially lost all function in his left arm and most of the function in his left leg, and had difficulty controlling his emotions during speech. "He would kind of cry-talk for a while," says Kobrine. Brady also had memory and thinking deficits, such as problems recognizing people. But 30 years after the shooting, he can walk and has regained almost all of his prior speech and cognitive function, says Kobrine.

However, Giffords faces a special challenge because she is a woman. "Women tend to have a more protracted and less complete recovery than men, for reasons that nobody clearly understands," says O'Shanick.

And even if Giffords recovers most of her movement and thinking skills, she could suffer from a range of other lifelong complications; for example, she will have an increased risk of developing dementia or Parkinson's disease. Up to 50% of people who have a penetrating brain injury also go on to develop epilepsy, perhaps because bleeding in the brain after an injury exposes it to high doses of seizure-associated chemicals called haemosiderins, which arise as haemoglobins in the blood break down. Many patients with injuries to the left sides of their brains also experience depression, because a region on the left front of the brain is involved in mood control.

Perhaps the most famous brain-injury survivor in history is Phineas Gage, the American railroad foreman who lived to tell the tale after an explosion drove an iron bar through his head in 1848. He is said to have suffered from depression after the injury, and he died in 1860 as a result of epileptic seizures brought on by the event.

Whatever the complications that Giffords suffer, the road to recovery will be long. "This will undoubtedly be a lifelong issue for her," says O'Shanick.