DALLAS (Reuters) -- One of the Egyptian twins formerly conjoined at the crown of their heads was put back on a mechanical ventilator, and his brother was recovering strength in his limbs, doctors said on Wednesday.

Dr. James Thomas, chief of critical care services at Children's Medical Center in Dallas where 2-year-old Ahmed and Mohamed Ibrahim were separated on Oct. 12, said Ahmed was placed back on the ventilator after being removed from the device on Tuesday.

Ahmed initially did well after being removed and smiled at his father, Thomas said, but swelling in his throat made it difficult for him to breathe on his own.

"This represents a minor complication of mechanical ventilation and doesn't affect his neurological recovery," Thomas said.

Mohamed has been off a ventilator since the weekend and is regaining movement in the right side of his body, which has been weak since he regained consciousness last week.

"Physicians, nurses and therapists caring for the boys continue to be optimistic about their progress," Thomas said.

Both boys have shaken a low-grade fever and have been taken off of antibiotics.

It will take weeks to determine if they suffered any brain damage from an operation in which a team of five neurosurgeons separated brain material the boys shared as well as the shared circulatory systems that fed blood to their brains.

The boys were born in a town 500 miles south of Cairo on June 2, 2001.