Dreadwing and Skyquake were twins with a split spark. When Skyquake was awakened and killed, Dreadwing felt it too. In Armada we saw how when Starscream's clones got hurt the original felt the pain. In human biology identical twins are similar to clones, it seems the same way in cybertronian biology. So it stands to reason that those protoforms that starscream discovered had no sparks. When they became clones....they used starscream's spark, since their deaths and pain was linked to the original, much like Skyquake/Dreadwing. If the clone managed to kill starscream it may have killed itself...simply because that's where its spark is... But since the clones and starscream didn't share memories after the clones were created it seems that the brain of the cybertronian contains the memories.