Timing of babies distinguishing touch from pain identified
MedWire News: Infants begin to distinguish between touch and pain just before birth, at between 35 and 37 weeks of gestation, report researchers who explain that before this time, neonatal brains merely exhibit nonspecific neuronal bursts.
The findings of the study, involving term and preterm neonates, indicate that excess amounts of noxious (painful) activities undertaken during neonatal intensive care could disrupt the normal formation of babies' cortical circuits.
Furthermore, this could be the mechanism "underlying the long-term neurodevelopmental consequences and altered pain behavior in ex preterm children," suggest Lorenzo Fabrizi (University College London, UK) and colleagues.
Recent studies in developing brain networks show the importance of neuronal bursting in the formation of functional circuits, as they precede the onset of sensory functions, remarks the team in the journal Current Biology.
However, evidence of these processes in the human brain and the timing of infant discrimination between touch and pain are lacking.
Fabrizi and co-investigators therefore characterized the brain activity of 18 term infants aged 37-45 weeks gestation and 21 preterm infants aged 28-36 weeks gestation in their response to tactile (touch), and noxious (clinically necessary heel lance for blood sampling) input, using electroencephalograms (EEGs).
Principal component analysis showed that the percentage of preterm infants with specific neural activity on the EEG relating to tactile- or noxious-specific input was significantly lower than that seen in term infants, at 7% and 33%, versus 30% and 63%, respectively.
The respective latencies between touch or noxious input and brain activity were an average 31 and 40 ms shorter in full-term infants than in preterm infants.
Next, the research team investigated the occurrence of neuronal bursts - defined as a significant change from the baseline energy occurring simultaneously in the low-frequency and high-frequency bands at any electrode site within the first 1.5 s after stimulation.
Spontaneous neuronal bursts were recorded in 13% of 30 background EEG epochs in preterm infants, while both touch and noxious lance increased the occurrence of bursts, and did so to a greater extent following noxious lance than touch, at 57% versus 27%.
In full-term infants, fewer (10% of 30 background EEG epochs) showed neuronal bursting activity, and increases in the response after stimulation was significantly less common than among preterm infants, at 10% and 13% after touch and noxious lance, respectively.
"The clearly defined specific noxious-evoked potentials recorded in older infants in response to heel lance, in contrast to the nonspecific increase in neuronal bursts characteristic of early prematurity, are therefore likely to reflect the maturation of the functional brain circuitry that enables the human brain to discriminate noxious stimuli from other forms of sensory input," conclude Fabrizi and co-authors.
By Sarah Guy