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Babies’ capacity for pain may form around time of birth

Sept. 8, 2011
Courtesy of Cell Press
and World Science staff

A new study sug­gests in­fants may de­vel­op the abil­ity to sense pain a few weeks be­fore their nor­mal due dates.

“Ba­bies can dis­tin­guish pain­ful stim­u­li as dif­fer­ent from gen­er­al tou­ch from around 35 to 37 weeks gesta­t­ion—just be­fore an in­fant would nor­mally be born,” said Lo­ren­zo Fab­rizi of Uni­vers­ity Col­lege Lon­don. Re­port­ing their find­ings on­line Sept. 8 in the re­search jour­nal Cur­rent Bi­ol­o­gy, Fab­rizi and col­leagues say the re­sults may have im­plica­t­ions for clin­i­cal care. They might al­so be cited in de­bates over wheth­er abor­tion should be le­gal.

The researchers meas­ured preterm in­fants’ re­sponses to a pain stim­u­lus that they said was med­ic­ally un­avoid­a­ble for them—a prick of the heel to get a blood sam­ple. Since ba­bies can’t tell you wheth­er some­thing hurts, the re­search­ers used record­ings of elec­tri­cal brain ac­ti­vity, a tech­nique called elec­tro­en­ceph­a­lo­graphy. 

Ac­cord­ing to the in­ves­ti­ga­tors, re­cent stud­ies have em­pha­sized the im­por­tance of bursts of nerve ac­ti­vity, both spon­ta­ne­ous and stim­u­lus-evoked, as func­tion­al brain cir­cuit­ry forms. The burst­ing pat­tern shifts in de­vel­opment to adult-like re­sponses that are more spe­cif­ic to par­tic­u­lar sen­so­ry in­puts.

Tests on in­fants be­tween 28 and 45 weeks gesta­t­ion show the brain starts to re­spond dif­fer­ently to a sim­ple tou­ch and the heel prick at about 35 to 37 weeks, the in­ves­ti­ga­tors said. Ba­bies’ due dates are based on 40 weeks of preg­nan­cy, and ba­bies are gen­er­ally con­sid­ered full term at 37 weeks.

The re­sults may have im­plica­t­ions for the treat­ment, care, and de­vel­opment of prem­a­ture new­borns, Fab­rizi said, not­ing that these chil­dren can of­ten grow up to be ei­ther more or less sen­si­tive to pain than usu­al.

“Re­peated nox­ious stimula­t­ion of the kind used in this study is a fea­ture of ne­o­na­tal in­ten­sive care,” the re­search­ers wrote. “Our find­ing that nox­ious heel lance [prick] in­creases neu­ronal burst­ing ac­ti­vity in the brain from the ear­li­est age raises the pos­si­bil­ity that ex­cess nox­ious in­put may dis­rupt the nor­mal forma­t­ion” of brain cir­cuits. The work, they added, also suggests such dis­rup­tion could ex­plain “the long-term neu­ro­de­vel­opmental con­se­quenc­es and al­tered pain be­hav­ior in ex-preterm chil­dren.”


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A new study suggests infants may develop the ability to sense pain a few weeks before their normal due dates. “Babies can distinguish painful stimuli as different from general touch from around 35 to 37 weeks gestation—just before an infant would normally be born,” said Lorenzo Fabrizi of University College London. Reporting their findings online Sept. 8 in the research journal Current Biology, Fabrizi and colleagues say the results may have implications for clinical care. They may also bear on debates over whether abortion should be legal. Fabrizi and colleagues measured infants’ responses to a pain stimulus that was medically unavoidable for them, in which the heel was pricked to get a blood sample. Since babies can’t tell you whether something hurts, the researchers used recordings of electrical brain activity, a technique called electroencephalography. According to the investigators, recent studies have emphasized the importance of bursts of nerve activity, both spontaneous and stimulus-evoked, as functional brain circuitry forms. The bursting pattern shifts in development to adult-like responses that are more specific to particular sensory inputs. Tests on infants between 28 and 45 weeks gestation show the brain starts to respond differently to a simple touch and the heel prick at about 35 to 37 weeks, the investigators said. Babies’ due dates are based on 40 weeks of pregnancy, and babies are generally considered full term at 37 weeks. The results may have implications for the treatment, care, and development of premature newborns, Fabrizi said, noting that these children can often grow up to be either more or less sensitive to pain than usual. “Repeated noxious stimulation of the kind used in this study is a feature of neonatal intensive care,” the researchers wrote. “Our finding that noxious heel lance [prick] increases neuronal bursting activity in the brain from the earliest age raises the possibility that excess noxious input may disrupt the normal formation of cortical circuits, and that this is a mechanism underlying the long-term neurodevelopmental consequences and altered pain behavior in ex-preterm children.”