One of the separated Egyptian twins has sat up for the first time in his life.
His brother is set to be removed from a mechanical ventilator by a medical team, doctors said on Monday.
Dr James Thomas, director of critical care at Children's Medical Centre in Dallas where Ahmad and Muhammad Ibrahim were separated on 12 October, said the two-year-old boys were following a different path to recovery.
They were both in remarkable condition after being separated at the crown of their head by a team of 18 doctors in a 34-hour operation, he said.
Muhammad, who has recovered at a quicker pace, was able to sit up with the help of a therapist.
Due to the way the boys were joined at the head, it was impossible for them to sit, and without separation surgery, they probably would have never been able to walk.
"Because the boys are twins, people focus on their similarities and expect them to follow similar clinical courses," said Thomas.
"However, the two boys are different in many ways, including their responses to complex neurological surgery."
Thomas said doctors were hoping to take Ahmad off a mechanical ventilator on Monday.
Muhammad was removed from the device on Sunday and has been a little more alert than his brother.
Both boys were listed in critical but stable condition and they are both running a low-grade fever. Thomas said doctors may soon upgrade the boys' condition to guarded from critical.
Dr Thomas says doctors may soon
upgrade the boys' condition to
guarded from critical
It will take weeks to see if the boys suffered any brain damage from an operation where a team of five neurosurgeons separated brain material they shared, as well as the shared circulatory systems that feed blood to their brains.
One of the major challenges for doctors will be reconstructing the area at the top of their heads where there is no skull - but there is a flesh covering. Both boys will soon be fitted for protective helmets.
"Compared to their dramatic improvement of the past week, the twins' progress now may seem slower," Thomas said.
The boys were born in a town 800km south of Cairo on 2 June 2001.