Sen. Tim Johnson has been transferred out of intensive care and has started to speak, his doctor said Thursday, nearly a month after the South Dakota Democrat suffered a brain hemorrhage.

An MRI on Tuesday showed the speech centers in the senator's brain were spared injury in the initial hemorrhage Dec. 13, said Johnson's neurosurgeon, Dr. Vivek Deshmukh.

"This is confirmed by the fact that he is following commands and has started to say words," Deshmukh said in a statement released by Johnson's office.

Johnson will be participating in "aggressive therapy" in the inpatient rehabilitation unit at George Washington University Hospital, the statement said.

"The fact that Tim is beginning to use words is remarkable as is his strength and determination," said his wife, Barb Johnson. "He even maintains his sense of humor when I share e-mails about his grandsons' adventures."

On Monday the senator's condition was upgraded from critical to fair, and his doctors said he no longer needed a ventilator to help him breathe. He is being weaned off the tracheotomy tube that remains in his neck, his office said Wednesday.

His office has said that his recovery is expected to take several months.

Johnson was diagnosed with the arteriovenous malformation, a condition, often present from birth, that causes arteries and veins to grow abnormally large, become tangled and sometimes burst. He was rushed to the hospital after becoming disoriented on a phone call with reporters, and he underwent emergency surgery hours later.

His long-term prognosis is unclear. Doctors have said he is steadily improving and has been responsive to his family and physicians, following commands, squeezing his wife's hand and understanding speech. He needed the ventilator to assist with his breathing after fluid developed in his lungs as a consequence of his initial hemorrhage, his doctors said.

In cases like Johnson's, doctors often depend on the patient's ability to answer questions to assess any cognitive damage caused by the hemorrhage.

Johnson's sudden illness raised questions about the Democrats' one-vote majority in the upcoming Senate session. South Dakota's Republican governor, Mike Rounds, would appoint a replacement if Johnson's seat were vacated by his death or resignation.

A Republican appointee would create a 50-50 tie and could effectively allow the GOP to retain Senate control because of Vice President Dick Cheney's tie-breaking vote.