In a Time magazine article, which profiled the brothers, the scientific mission was discussed as well (Mikhail Kornienko is a cosmonaut on the ISS):
On this flight, the time for distractions may be especially tight, thanks to the battery of 10 medical and psychological tests that will be on the agenda for both Scott and Kornienko in orbit and for Mark on the ground. Flight surgeons will run studies of cardiovascular efficiency, blood-oxygen levels and blood volume. Bone density will be monitored, as well as cellular aging and fluid shifts in the body. Sonograms will be taken of the eye and optic nerve to determine how those shifts affect vision.
Mood and mental shifts will also be measured throughout the mission. All of which should contribute to a better understanding of the effects of space travel. I doubt NASA has many twin astronauts waiting in the wings, so this is a unique opportunity to prepare for future manned space travel. We will all be watching.
