We are a Cartesian civilization. We truly are at the point of I think therefore I am. It is the basis of our laws that allows us to turn off life support. When the brain does not function you are no longer a person. And I don't mean retardation or alzheimers or any other bullshit strawman you are going to pull out of your ass. I mean that when the higher brain function ceases or is not there in the first place we are not persons. Terry Schiavo was a prime example of this. Her brain had shrunk, her optical nerves had died and rotted away in her head. She had ONLY brainstem function which means she had NO awareness. People talked about her smiling, that is brainstem activity and children that are born anacephalitic also smile and even suckle because it is all lower brain activity. The difference between a person and a fetus is that the fetus is not even capable of higher brain activity.
Second-trimester brains do not have the full complement of neurons yet, and thus do not have the gyri and sulci (cords and grooves, giving more surface area) on the surface of the brain. Fetal movements become possible in the 4th month. Spinal-level reflexes (the kind elicited by the doctor with the rubber hammer) can occur in the 2nd trimester, but some reflexes aren't fully mature until after birth. Cerebellum and spinal cord are also developing, and coordinated movement takes longer to develop.
http://www.io.com/~wwwomen/abortion/develop.html