When do humans begin to feel pain?

The U.S. House Of Representatives recently passed a bill that would restrict abortions starting at 20 weeks after fertilization, or the stage of development shown in the picture on the right. Formally called the “Pain-Capable Unborn Child Protection Act,” the legislation has stirred debate over when humans begin to feel pain. The act passed with 97% of Republicans voting for it, and 97% of Democrats voting against it. President Obama has issued a veto threat.

The bill states “there is substantial medical evidence that an unborn child is capable of experiencing pain at least by 20 weeks after fertilization, if not earlier.” However, Dr. Stuart Derbyshire, the director of Pain Imaging at the U.K.’s University of Birmingham and a frequently cited authority on this issue,has affirmed that humans cannot truly feel pain until one year after birth. Contrastingly, Dr. Maureen Condic, an associate professor of neurobiology and anatomy at the University of California, Berkeley, recently testified before a congressional subcommittee that humans feel pain “in some capacity” starting “from as early as 8 weeks of development.”

In sorting out these conflicting assertions and others on the continuum between them, there are certain scientific facts about human development that provide a basic foundation for understanding this issue:

• In the 6th and 7th weeks after fertilization, the brain’s “cerebral hemispheres and cerebellum are developing.” [Gray’s Anatomy: The Anatomical Basis of Medicine and Surgery]
• By 7 weeks, pain “sensory receptors appear in the perioral [mouth] area.” [New England Journal of Medicine]
• By 10 weeks, “All components of the brain and spinal cord are formed, and nerves link the stem of the brain and the spinal cord to all tissues and organs of the body.” [Encyclopedia of Human Biology]
• By 12 weeks, “the fetus sucks its thumb, kicks, makes fists and faces, and has the beginnings of baby teeth.” [Human Genetics: Concepts and Applications]
• By 14 weeks, “Limb movements, which occur at the end of the embryonic period (8 weeks), become coordinated….” [Before We Are Born: Essentials of Embryology and Birth Defects]
• By 16 weeks, “Eye movements begin.” [Embryology: Board Review Series]
• By 18 weeks, pain sensory receptors spread to “all cutaneous [skin] and mucous surfaces….” [New England Journal of Medicine]
• By 20 weeks, the fetus “now sleeps and wakes and hears sounds.” [American Medical Association Complete Medical Encyclopedia]

Additionally, evidence from the burgeoning field of fetal surgery has shown that preborn humans react to physical provocations (like being jabbed with a needle) in the same ways as children and adults, which includes releasing stress hormones, shunting blood to the brain, and pulling away from the source of the provocation. Per a 2012 paper in the journal Fetal Diagnosis and Therapy, “A physiological fetal reaction to painful stimuli occurs from between 16 and 24 weeks’ gestation on.” Likewise, a 2001 paper in the journal Anesthesiology explains that “the human fetus from 18-20 weeks elaborates pituitary-adrenal, sympatho-adrenal, and circulatory stress responses to physical insults.”

Taken together, the facts above would seem to imply that by 20 weeks or earlier, humans have the capacity to feel pain. However, some scientists have argued otherwise using two main lines of reasoning. Both of these have critical flaws.

The first argument centers upon the development of the cerebral cortex, which is the portion of the brain associated with functions such as reasoning, language, and memory. In the words of a panel convened by the U.K.’s Royal College of Obstetricians & Gynecologists, the cortex is essential to “perception or awareness,” and therefore, a connection from the body’s pain receptors to the “cortex is necessary for pain perception.” Since these connections “are not intact before 24 weeks of gestation,” the “fetus cannot experience pain in any sense prior to this gestation.”

This issue gets complicated, but in short, there may well be communication between the body’s pain receptors and the cortex long before 24 weeks; it’s just that the connections and cortex are not fully developed. As explained in a 2012 paper in Fetal Diagnosis and Therapy, “From 16 weeks’ gestation pain transmission from a peripheral [pain] receptor to the cortex is possible and completely developed from 26 weeks’ gestation.” Per correspondence with an author of this paper, these developmental milestones (16 weeks and 26 weeks) are measured from the last menstrual period, which equates to 14 weeks and 24 weeks after fertilization.

Far more importantly, the claim that the cortex is essential to “perception or awareness” has been undercut by recent research, which has shown that children born with little or no functional cortical tissue (a condition called hydranencephaly) do, in fact, have perception and awareness. Although the cortex is commonly called the “organ of consciousness,” a 2006 paper in the journalBehavioral and Brain Sciences has shown that:

• “An infant born with hydranencephaly may initially present no conspicuous symptoms,” and “occasionally the condition is not diagnosed until several months postnatally, when developmental milestones are missed.”
• These children are not only awake and often alert, but show responsiveness to their surroundings in the form of emotional or orienting reactions to environmental events…. They express pleasure by smiling and laughter, and aversion by ‘fussing,’ arching of the back and crying (in many gradations), their faces being animated by these emotional states. … The children respond differentially to the voice and initiatives of familiars, and show preferences for certain situations and stimuli over others, such as a specific familiar toy, tune, or video program….”
• “The evidence and functional arguments reviewed in this article are not easily reconciled with an exclusive identification of the cerebral cortex as the medium of conscious function. … The tacit consensus concerning the cerebral cortex as the ‘organ of consciousness’ would thus have been reached prematurely, and may in fact be seriously in error.”

In summarizing the above evidence along with other facts relevant to this issue, a 2006 article inPain: Clinical Updates states, “Multiple lines of evidence thus corroborate that the key mechanisms of consciousness or conscious sensory perception are not dependent on cortical activity. Consistent with this evidence, the responses to noxious stimulation of children with hydranencephaly are purposeful, coordinated, and similar to those of intact children.”

The second argument, as articulated by the Royal College of Obstetricians & Gynecologists (RCOG), is that “the fetus never experiences a state of true wakefulness in utero and is kept, by the presence of its chemical environment, in a continuous sleep-like unconsciousness or sedation.” Ten pages into RCOG’s study, it is disclosed that this conclusion is “derived largely from observations of fetal lambs.”

Opposing that line of evidence are studies of humans that have found conscious, deliberate behaviors from as early as 14 weeks gestation. Revealingly, in a 2010 study published in the journal PLoS ONE, a cross-disciplinary team of scientists used 4-D ultrasound to record and scrutinize the interactions of preborn twins. They found that:

• “Starting from the 14th week of gestation twin fetuses plan and execute movements specifically aimed at the co-twin.”
• These “early contacts do not occur accidentally, but reflect motor planning.”
• “These findings force us to predate the emergence of social behavior….”

An article in the journal Science summarized the study as follows: “The findings suggest that twin fetuses are aware of their counterparts in the womb and prefer to interact with them.”

In summary, the scientific evidence converges upon the conclusion that preborn humans can feel pain from 20 weeks after fertilization or earlier. While this does not rise to the level of 100% certainty, it rests upon factually solid ground.

The article originally appeared at JustFacts and is reprinted with permission.