When Infants Gain the Capacity for Pain

ScienceDaily (Sep. 8, 2011) — A new study has for the first time revealed the time in development when infants appear able to tell the difference between pain and basic touch. The researchers, who report their findings online in the Cell Press journal Current Biology on Sept. 8, say that the results, based on recordings of brain activity in preterm infants, may have implications for clinical care.

The evidence suggests that developing brain networks become mature enough to identify pain as distinct from touch fairly late in development.
"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.
Infants can't actually tell you whether something hurts or not, so the researchers relied on recordings of brain activity by electroencephalography (EEG).
According to the researchers, recent studies have emphasized the importance of bursts of neuronal activity, both spontaneous and evoked, during the formation of functional brain circuitry. That bursting pattern of activity shifts in development to adult-like responses that are more specific to particular sensory inputs.
EEG recordings of infants between the ages of 28 to 45 weeks gestation show that the brain begins to produce distinct responses to a simple touch versus a clinically essential heel lance considered as painful at about 35 to 37 weeks gestation. (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 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."

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Story Source:

The above story is reprinted from materials provided by Cell Press, via EurekAlert!, a service of AAAS.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.

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Journal Reference:

1. Lorenzo Fabrizi, Rebeccah Slater, Alan Worley, Judith Meek, Stewart Boyd, Sofia Olhede, Maria Fitzgerald. A Shift in Sensory Processing that Enables the Developing Human Brain to Discriminate Touch from Pain. Current Biology, 2011; DOI:10.1016/j.cub.2011.08.010

summary here

A Shift in Sensory Processing that Enables the Developing Human Brain to Discriminate Touch from Pain

article here

Current Biology, Volume 21, Issue 18, 1552-1558, 08 September 2011
Copyright © 2011 Elsevier Ltd All rights reserved.
10.1016/j.cub.2011.08.010

Authors

Lorenzo Fabrizi,Rebeccah Slater,Alan Worley,Judith Meek,Stewart Boyd,Sofia Olhede,Maria FitzgeraldSee Affiliations

• Highlights
• The human brain may discriminate touch from pain from 35–37 weeks gestation
• Before 35–37 weeks, touch and noxious lance evoke nonspecific neuronal bursts
• After 35–37 weeks, touch and noxious lance evoke modality-specific potentials

Summary

When and how infants begin to discriminate noxious from innocuous stimuli is a fundamental question in neuroscience [1]. However, little is known about the development of the necessary cortical somatosensory functional prerequisites in the intact human brain. Recent studies of developing brain networks have emphasized the importance of transient spontaneous and evoked neuronal bursting activity in the formation of functional circuits [2,3]. These neuronal bursts are present during development and precede the onset of sensory functions [4,5]. Their disappearance and the emergence of more adult-like activity are therefore thought to signal the maturation of functional brain circuitry [2,4]. Here we show the changing patterns of neuronal activity that underlie the onset of nociception and touch discrimination in the preterm infant. We have conducted noninvasive electroencephalogram (EEG) recording of the brain neuronal activity in response to time-locked touches and clinically essential noxious lances of the heel in infants aged 28–45 weeks gestation. We show a transition in brain response following tactile and noxious stimulation from nonspecific, evenly dispersed neuronal bursts to modality-specific, localized, evoked potentials. The results suggest that specific neural circuits necessary for discrimination between touch and nociception emerge from 35–37 weeks gestation in the human brain.