CINCINNATI (AP) _ An infant has shown increased development in the nine weeks since since surgeons removed half his brain in an attempt to end his potentially deadly seizures, his doctor says.

Dr. Kerry Crone said Monday it is too soon to tell much about the eventual mental development of Brent Hammergren. But since the surgery was performed so early in his life, the 7-month-old boy's body will naturally transfer some functions of the brain's missing right side to the remaining left half, Crone said.

Crone said Brent's development remains about three months behind because of time lost to the seizures.

''There will be some weakness, I'm sure, but I think it'll be functional for him,'' Crone said.

Brent's mother, who cuddled the cooing boy at a news conference Monday, said she has noticed remarkable improvement in his reactions since the surgery.

''He never used to follow me and smile when I was in the room. Now, to look at him and see him smile - it just melts you,'' Kimberly Hammergren said. ''He reaches for his toys. He has oodles of toys, but he never played with them.''

Crone, a pediatric neurosurgeon, said he and other doctors at Children's Hospital Medical Center performed the Dec. 30 operation because the infant suffered from a rare developmental ailment that caused frequent and potentially deadly seizures. Drug treatments did not stop the seizures.

Crone said removing the right side of the brain from an older person would paralyze the body's left side and eliminate other functions associated with the brain's right side, including creativity.

The child, who returned to his suburban Evendale home Jan. 16 with his mother and father, Thomas, is to begin outpatient therapy this week, said Crone, who has been seeing the infant three times a week to monitor his progress.

Hospital officials said it is the first known case in the United States - the second worldwide, after one in Scotland - in which a child with Brent's disorder not only survived the surgery but apparently benefited from it.

Two similar operations have been performed since 1978 in Canada and Germany, Crone said. In one case, the child died shortly after surgery. In the other, the child lived 2 1/2 years after the operation but exhibited almost no functions, Crone said.

Brent began having seizures 13 days after he was born July 21. The seizures continued and increased in number and intensity, totaling up to 130 in a row before his operation, his parents said. Doctors identified his disease as hemimegalencephaly.

He was suffering virtually constant seizures, putting him in a coma-like state, Crone said.

The space left in Brent's head by removal of the brain portion was filled partly by expansion of the remaining brain part and by fluids the surgeons injected, Crone said.