Cornelissen, L.L.; (2011) Spinal sensory processing in the human infant: development of the flexion withdrawal reflex. Doctoral thesis , UCL (University College London).

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Abstract

Immature spinal sensory reflexes have lower mechanical thresholds and are poorly coordinated and exaggerated compared to adult reflexes. However, little quantitative data is available on how these spinal sensory circuits develop in the human infant. This thesis investigates the development of cutaneous flexion withdrawal reflexes in preterm and fullterm human infants following noxious and non-noxious stimulation of the heel, and tests whether flexion withdrawal reflex activity is modulated by the commonly administered analgesic, oral sucrose, in a randomised controlled trial. The studies were undertaken in infants aged 28-45 weeks gestation (GA), in-patients at University College Hospital, London. The noxious stimulus was a clinically required heel lance; non-noxious stimulation was either a light touch of the heel or application of calibrated von Frey hairs to the heel. Flexion withdrawal reflex activity was recorded with surface EMG electrodes placed over the biceps femoris muscle. Video recordings of facial expression were recorded for clinical pain assessment. Noxious heel lance evoked bilateral withdrawal reflex activity across all ages, but the peak amplitude was greater in preterm infants (<37 weeks GA) than full-term infants (>37 weeks GA). Nociceptive reflex activity occurred even when there was no change in facial expression. Non-noxious touch evoked a significantly smaller reflex response than noxious stimulation. The von Frey hair cutaneous mechanical threshold for flexion withdrawal reflex activity increased with gestational age. Repeated stimulation with von Frey hairs at suprathreshold intensities caused greater habituation in full term than preterm infants. Flexion withdrawal reflex properties were not altered by administration of oral sucrose before a heel lance, despite significant reduction in clinical facial expression scores. In conclusion, human spinal sensory circuits undergo significant postnatal development that alters their behavioural responses to touch and pain. The commonly used neonatal analgesic, oral sucrose, does not affect sensory processing at the level of the spinal cord.

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