The 1-year-old Guatemalan twins born joined at the head and separated in a lengthy surgery opened their eyes and began moving Thursday, one of their doctors said.

Maria de Jesus Quiej Alvarez and sister Maria Teresa remained on breathing devices and in critical condition at the University of California Los Angeles Medical Center.

Both have opened their eyes and move in response to stimulation, said Dr. Andy Madikians, head of pediatric intensive care at UCLA's Mattel Children's Hospital.

"I think what we're seeing is what we expect to see at this point," Madikians said.

Maria Teresa, who had nearly five additional hours of surgery because of blood on the brain, wasn't moving as much as her sister, the doctor said.

Maria de Jesus was the first to show some movement. Earlier Thursday, the hospital said she fluttered her eyes after doctors took the twins off the paralyzing drugs they had been given to prevent coughing and other movement that could injure their brains.

"We remain cautiously optimistic about the long-term prospects of Maria Teresa and Maria de Jesus," Madikians said. "There are still many medical hurdles to cross."

The girls were born in rural Guatemala to Alba Leticia Alvarez, 23, and Wenceslao Quiej Lopez, a 21-year-old banana packer.

The girls were attached at the top of the skull and faced opposite directions. They shared bone and blood vessels but had separate brains. Cases like theirs happen in fewer than one in 2.5 million live births.

The two still face follow-up operations to reconstruct their skulls.

Healing the Children, a nonprofit group in Spokane, Wash., brought the babies to the hospital, and many UCLA doctors donated their services. But $1.5 million in hospitalization costs remain to be covered.