Doctors saw some evidence of brain damage in Indiana Gov. Frank O'Bannon (search), a hospital spokeswoman said Tuesday, a day after O'Bannon suffered a massive stroke.

With the 73-year-old governor in a drug-induced coma and on a ventilator, doctors said Monday that the next day or two would be critical.

Northwestern Memorial Hospital (searchspokeswoman Kelly Sullivan said Tuesday that doctors saw reflex movement that indicates brain damage. "It's too soon to tell exactly the extent of the damage," she said.

"This is up to Mother Nature and his own ability to bounce back, his own brain's ability to recover," Dr. Hunt Batjer, chairman of neurological surgery at Northwestern, said earlier.

Lt. Gov. Joe Kernan (search) assumed O'Bannon's duties as acting governor. "I would just ask all Hoosiers to join hands and say a prayer," he said.

And Indiana's first lady thanked residents for their support.

"We have often said there is no limit to where we can go when we go together," Judy O'Bannon said in a statement. "Words cannot describe the comfort we feel from the people of Indiana and beyond and we truly feel we are on this journey together."

O'Bannon, a Democrat in his second term, was found Monday morning on the floor of his Chicago hotel room in his pajamas. He was unconscious and near death when he was rushed to the hospital, doctors said. He remained in critical condition midmorning Tuesday.

O'Bannon suffered a cerebral hemorrhage, a type of stroke caused by bleeding in the brain. Pressure on the brain is a major complication of such an injury and patients are often placed in drug-induced comas to help relieve the pressure and allow the brain to rest and heal.

O'Bannon is expected to remain under the sedation for at least several days, Sullivan said.

Dr. Wesley Yapor said surgeons removed blood from both sides of O'Bannon's brain during three hours of surgery Monday. Some of the bleeding probably came from an injury, suggesting that the governor fell after becoming ill, he said. Sullivan said the surgery was successful.

Doctors said it was too early to predict the likelihood of O'Bannon fully recovering. The outcome depends on how much bleeding occurs, how much of the brain is affected, and how long the patient goes without treatment.

Strokes are the nation's leading cause of disability in the United States and the No. 3 killer. Most are ischemic strokes, caused when arteries feeding the brain are blocked, but some are caused by bleeding in the brain. Survivors often suffer permanent disability including paralysis and loss of speech.

O'Bannon was staying at the Palmer House Hilton in Chicago to attend a conference of the Midwest U.S.-Japan Association (search).

Kernan became acting governor under a provision in the state constitution that allows him to temporarily carry on business without a formal transfer of power.

State officials said Tuesday they believe the formal transfer, which requires a petition from legislative leaders and state Supreme Court approval, would be needed if O'Bannon was never able to return to work.

In his seven years as governor, O'Bannon, a moderate known for grandfatherly charm, has forged alliances to reform education and try to improve the state's economy.

The governor coasted to re-election in 2000, but his popularity began to slide in his second term as the economy faltered. He is barred by term limits from running again next year.

"It will be a real shock if he doesn't recover," said Kim Self, sales manager at Magdalena's Restaurant & Gourmet Gift Shop in the southern town of Corydon, O'Bannon's home.

The last time Indiana had an acting governor for any length of time was in 1924, when the incumbent, Gov. Warren McCray, was forced to resign after being convicted of mail fraud.