Some ethicists say a human life begins when the brain stem is born. The development of the brain stem probably is responsible for most of the embryo’s movements, which begin about six weeks after conception and include a general fluttering of the body, known as the startle reflex.Īt this point, the embryo does not have the upper portions of the brain that allow a person to intentionally move a part of his body, according to Michael Bennett, neuroscience chairman at Albert Einstein Medical School in the Bronx, N.Y. This portion of the brain-once a person is born-regulates breathing, blood pressure, heartbeat and primitive reflexes such as swallowing and the pupils’ response to light.Ī new study by O’Rahilly has shown that by eight weeks the brain stem of the embryo looks “extraordinarily similar to that of a newborn baby.” About this point, the 1 1/4-inch embryo has a face, hands and feet that also look, at first glance, like those of a human baby. When an embryo reaches the seventh week, the first fully developed nerve cells, called neurons, can be found topping the spinal cord and forming the brain stem, according to Ronan O’Rahilly, director of the Carnegie Laboratories of Embryology at UC Davis. (All ages of embryos or fetuses in this article are days or weeks since conception, not gestational age.) The first brain cells do not appear in a human embryo until close to the third week after conception, and studies indicate that the thinking and sensing portions of the brain where awareness resides do not click on until after the 28th week.
When does a fetus have brain activity full#
“Prenatal life is full of changes, by nature, and any of those changes may be of moral significance,” Flower added. “What we take ourselves to be as persons,” said developmental biologist Michael Flower of Lewis and Clark College in Portland, Ore., “are capacities made possible by our brains.” In a recent paper, Flower outlined the stages of brain development in the embryo and fetus and their implications for the abortion debate. The Roman Catholic Church claims conception is life’s starting point, whereas most current abortion laws are keyed to when the fetus might survive if born prematurely (at the end of the second trimester).īut armed with the latest findings on fetal development, some scientists argue that “brain birth” in the fetus should mark the beginning of human life, just as “brain death” already is used to define the end of life. As the dramatic abortion debate plays out in courtrooms and legislatures across the nation, a basic and vitally important question arises ever more insistently-when does human life begin?