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NEONATAL SOCIETY ABSTRACTS

Noxious stimulation causes functional activation of the somatosensory cortex in newborn infants

Presented at the Neonatal Society 2004 Summer Meeting (programme).

Slater R1, Gallella S2, Boyd S3, Meek J2, Fitzgerald M1

1 Department of Anatomy and Developmental Biology, University College London, London, UK
2 Department of Paediatrics, University College London Hospital, London, UK
3 Neurosciences Unit, Institute of Child Health, London, UK

Introduction: Noxious sensations can clearly stimulate the central nervous system, producing reflex movements and a biochemical response, at a very early age (Fitzgerald, 1999, Smith, 2000). The true experience of pain requires functional maturation of higher brain centres, however, it is unclear at what CNS level this response is produced. Here we report on the use of near infra red spectroscopy (NIRS) to study the maturation of the cortical response to noxious sensation.

Aim: To use NIRS to investigate cortical pain processing in neonates using the haemodynamic response in the somatosensory cortex to noxious stimulation.

Methods: Eleven preterm infants were studied during routine phlebotomy. All infants had normal appearances on cranial ultrasound scans. The haemodynamic response to the heel lance was measured using a double channel NIR spectrophotometer. The optodes were positioned symmetrically on each side of the head over the somatosensory cortex and changes in oxyhaemoglobin (HbO2), deoxyhaemoglobin (HHb) and total haemoglobin (HbT) concentrations were measured.

Results: A haemodynamic response was successfully measured in seven infants with a mean post menstrual age (pma) of 36.3 weeks. Four studies were excluded due to motion artefact. Following the heel lance there was an increase in HbT in the contralateral somatosensory cortex and a decrease in the ipsilateral somatosensory cortex.


Table: showing maximum change in HbT in the contralateral and ipsilateral somatosensory cortex following painful stimulation. Figure: a sample trace of the evoked response in one infant.

Conclusion: Infants between 29 and 42 weeks pma show a large localised somatosensory response to painful stimulation. The magnitude of the evoked responses is similar to those obtained using visual and olfactory stimuli. This study shows that noxious stimulation evokes neural activity in the somatosensory cortex at this age and that both preterm and term infants are able to mount a cortical response to painful stimuli.

References:
1. Smith RP, Gitau R, Glover V, Fisk NM. 2000 Pain and stress in the human fetus.
Eur J Obstet Gynecol Reprod Biol. 92:161-5.
2. Fitzgerald M. 1999 The developmental neurobiology of pain. The textbook of pain, 4th edition. Ed Wall PD and Melzack R, Churchill Livingstone. pp 235-252

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