9 Furthermore, cortical activation can generate the experience of pain even in the absence of actual noxious stimulation. 9, 10 In support are functional imaging studies showing that activation within a network of cortical regions correlate with reported pain experience. 6 A lack of functional neuronal activity within the subplate calls into question the pain experience of a fetus before the penetration of spinothalamic fibres into the cortical plate.Ĭurrent theories of pain consider an intact cortical system to be both necessary and sufficient for pain experience. Spinothalamic projections into the subplate may provide the minimal necessary anatomy for pain experience, 8 but this view does not account for the transient nature of the subplate and its apparent role in the maturation of functional cortical connections. Subsequent dissolution of the subplate occurs through prolonged growth and maturation of associative connections in the human cerebral cortex. 6, 7 The major afferent fibres (thalamocortical, basal forebrain, and corticocortical) can wait in the subplate for several weeks, before they penetrate and form synapses within the cortical plate from 23-25 weeks' gestation. The subplate is a “waiting compartment,” required for mature connections in the cortex. Within the subplate, cortical afferents establish prolonged synaptic contacts before entering the cortical plate. The thalamic projections that develop from 12-16 weeks penetrate the subplate. By this stage the brain's outer layer has split into an outer cortical rim, with a subplate developing below. The first projections from the thalamus to cortex (the higher alarm) appear at 12-16 weeks' gestation. Without thalamic projections, these neuronal cells cannot process noxious information from the periphery. The neuronal cell density of the outer layer is much higher than that of a newborn infant or adult and at seven weeks' gestation has yet to receive any thalamic projections. 4, 5 The external wall of the brain is about 1 mm thick and consists of an inner and outer layer with no cortical plate. No laminar structure is evident in the thalamus or cortex, a defining feature of maturity. 3 An intact spinothalamic projection might be viewed as the minimal necessary anatomical architecture to support pain processing, putting the lower limit for the experience of pain at seven weeks' gestation.Īt this time, however, the nervous system has yet to fully mature. Whether the fetus can respond to a noxious stimulus with pain can thus be decided in part by determining when the alarm system is completely developed.įree nerve endings, the “alarm buttons,” begin to develop at about seven weeks' gestation 1, 2 projections from the spinal cord, the major “cable” to the brain, can reach the thalamus (the lower alarm) at seven weeks' gestation. The brain is the alarm that rings out pain. The electric cable from the button to the alarm is similar to the connection between the nerve endings and the brain.
WHEN DOES A FETUS GAIN SENTIENCE FREE
Viewed in this way, a noxious stimulus is an event that activates free nerve endings in the skin, similar to pushing an alarm button. Notwithstanding limitations, it is useful to view the pain system as an alarm system. The neurobiology of the fetus: anatomical pathways
The subjective experience of pain cannot be inferred from anatomical developments because these developments do not account for subjectivity and the conscious contents of pain. Although the developmental changes during these periods are remarkable they do not tell us whether the fetus can experience pain. Important neurobiological developments occur at 7, 18, and 26 weeks' gestation and are the proposed periods for when a fetus can feel pain. This paper discusses whether there is sufficient evidence to support a concept of fetal pain through an examination of fetal neurobiology and the relation to experience. Subsequent political and media discussion in the United Kingdom has debated changing abortion laws and procedures to mitigate against fetal pain. In the United Kingdom provocative images of the fetus generated by four dimensional ultrasonography have fuelled a reassessment of fetal capabilities along with suggestions that the fetus can respond both emotionally and cognitively. Doctors who fail to comply can be fined $100 000 (£57 700 €84 000) and can lose their licence and Medicaid funding. The US federal government is considering legislation that will require doctors to inform women seeking abortions that “there is substantial evidence that the process of being killed in an abortion will cause the unborn child pain.” w1 The bill mandates that a fetus of more than 22 weeks' gestational age should receive pain reducing drugs before an abortion.
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