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Next to all of this, the idea of using development of the brain, whose qualities ultimately distinguish us as human beings, to determine personhood seems eminently reasonable. And, says Sass, for the purpose of having a safety net we should pick "the earliest possible date, namely the first indication of formation of synapses in isolated areas of the brain." ¹⁶ Sass offers the date of seventy days after conception, saying this is when integrated brain functioning begins to emerge.

This date probably does provide for a generous margin of error, as embryologists place the date for earliest brain function a full two weeks later. "At about twelve weeks, electrical activity can be detected in the brain of the fetus, which could signal the dawn of consciousness," writes Austin. He, too, notes the symmetry between brain life and brain death. "Here, we would seem to have a very logical stage marking the start of a person, for the cessation of electrical activity in the brain ('brain death') is accepted in both medical and legal circles as marking the termination of a person — as an indication that life no longer exists in victims of accidents or in patients with terminal illnesses." ²

It is this electrical activity that members of the pro-life movement refer to when they claim — erroneously — that "brain waves are present before six weeks." ¹³ However, we are still talking about the most basic sort of brain activity, such as can be found in any living animal from tadpoles to antelope. It is not in any sense unique to humans, and therefore is subject to challenge as an appropriate factor for determining personhood.

Returning, then, to the development of the early embryo:

... a structure forms that biologists call the neural tube. It is a hollow cord of cells that runs along the central axis of the body, complete from head to tail after the first month (human embryos have tails for a while). One end of this tube bulges like the far tip of a long thin balloon being inflated. This area is called the brain, although until the second month of development the cells there do not become nerves; there are no special connections among them and there can be no thoughts. During the third and fourth months, nerve cells appear. Simple reflexes form first. The largest and most complex area of the brain, the cerebrum, develops last of all. ¹¹

Elaborating upon this, Sagan says, "thinking occurs ... principally in the top layers of the convoluted 'gray matter' called the cerebral cortex. The roughly one hundred billion neurons in the brain constitute the material basis of thought. The neurons are connected to each other, and their linkups play a major role in what we experience as thinking. But large-scale linking up of neurons doesn't begin until the twenty-fourth to twenty-seventh week of pregnancy — the sixth month." ¹⁹ Gardner concurs: "In the cerebrum, the mature brain cell pattern is not seen until the sixth or seventh month." ¹¹

"By placing harmless electrodes on a subject's head," continues Sagan,

... scientists can measure the electrical activity produced by the network of neurons inside the skull. Different kinds of mental activity show different kinds of brain waves. But brain waves with regular patterns typical of adult human brains do not appear in the fetus until about the thirtieth week of pregnancy — near the beginning of the third trimester. Fetuses younger than this — however alive and active they may be — lack the necessary brain structure. They cannot yet think. ¹⁹

Taking issue with misleading pro-life terminology, Grobstein says, "by brain waves, one usually means the kinds of regular electrical patterns that can be observed in adults. These do not exist in the early fetus. Until roughly thirty weeks you don't see the kind of regular patterns that are characteristic of EEGs in adults." ¹³

What this boils down to is "an early period of fetal development when you don't have to worry about a sentient being, because there's no anatomical or physiological basis for it. From eight to twenty weeks, the central nervous system is so extremely immature — especially the brain — that there seems no possibility of any awareness." ¹³

Then we have the period from twenty to thirty weeks, which Grobstein describes as "uncertain." "Once past the twenty-week mark, the brain is maturing and there are some connections between neurons in the cortex. We can be doubtful but we can't be sure there's no inner experience. That's where we need lots more information." Grobstein therefore suggests setting the "boundary of sentience" at twenty-six weeks to provide a safety margin, adding that on the evidence now available, "the dawn of sentience is far more likely to be later than ... earlier." ¹³

"If we are forced to choose a developmental criterion," say Sagan and Druyan, "then this is where we draw the line: when the beginning of characteristically human thinking becomes barely possible. It is, in fact, a very conservative definition: Regular brain waves are rarely found in fetuses... . If we wanted to make the criterion still more stringent, to allow for precocious fetal brain development, we might draw the line at six months." ¹⁹

Of course, at six months the fetus is unmistakably, even startlingly, human in appearance, a fact which has emotional connotations reaching far deeper than any application of logic. Still, it cannot hurt to keep this in mind:

The conscious mind is dauntingly complex, and [though] its workings are just now beginning to be understood, [w]e do know that the structure of the brain — the types and locations of its nerve cells and their interconnections — is intimately related to the function of the brain. The higher faculties must develop very late. Thoughts and feelings must arise very gradually. Thus, an embryo may have fingers, hands, a nose and eyes, even reflex movements, but still have no mind. ¹¹

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