Proceedings of The Physiological Society
Cardiff University (2009) Proc Physiol Soc 17, PC25
Noxious stimulation evokes delta brushes in human preterm infants
L. Fabrizi1, R. Slater1, S. Olhede2, A. Worley3, J. Meek4, S. Boyd3, M. Fitzgerald1
1. Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom. 2. Department of Statistical Science, University College London, London, United Kingdom. 3. Clinical Neurophysiology, Great Ormond Street Hospital for Children, London, United Kingdom. 4. Neonatal Intensive Care Unit, Elizabeth Garrett Anderson and Obstetric Hospital, University College London Hospital, London, United Kingdom.
Delta brushes are distinctive electroencephalographic (EEG) pattern of premature infants. They appear at 27 weeks, peak around 32-34 weeks and disappear around 44 weeks post-menstrual age (PMA) (1). Endogenous correlated neuronal activity and afferent inputs during prenatal and early postnatal brain development are the key factors of the organization of the functional cortical neuronal networks (2). Delta-brushes in human infants have been reported to be evoked in the controlateral somatosensory cortex by spontaneous limb movements and tactile stimulation, suggesting that they may be the result of a sensory feedback involved in the organization of the somatosensory cortex (3). While, under normal physiological conditions, sensory inputs are innocuous, premature infants in intensive care are frequently exposed to noxious stimuli, such as clinically required heel lances (4). Such intense and repeated stimulation may interfere with the normal balance of activity-dependent development of somatosensory circuits. If so, we hypothesise that noxious stimulation will alter the normal occurrence of delta-brush activity. EEG recordings were conducted on 16 premature neonates, 33-37 weeks PMA, born extremely prematurely (24-28 weeks PMA, n = 5) and prematurely (30-37 weeks PMA, n = 11) and on a control population of 7 full term newborns. Electrodes were placed at standard scalp positions according to the international 10-20 system. Five-second epochs, starting 2.5 seconds before event, corresponding to a noxious clinically-essential heel lance, an innocuous touch and no stimulation, were submitted to wavelet time-frequency analysis for automatic delta brush detection. Noxious stimulation evoked delta brush activity in 69% of the test occasions in premature infants (5/5 if born extremely prematurely and 6/11 if born prematurely), but innocuous touch in only 12% (1/5 and 1/11). Delta brush activity, when evoked by noxious stimulation, was always present in the temporal region (T3/T4) and never at the vertex (CPz/Cz) (9-54% of the times at other electrode sites). The spontaneous occurrence in premature infants was of 18% (0/5 and 3/11) and occurrence following noxious or innocuous stimulation in the control group was 14% (1/7). Noxious stimulation triggers delta brushes more frequently than innocuous stimulation, especially in the temporal region of the brain. It is therefore possible that noxious stimulation disturbs the normal organization of the somatosensory cortex during development. This is more likely in premature infants that were born extremely prematurely. However it is not clear if this is due to a longer hospitalization and related exposure to noxious stimuli or to differences in the development of the brain.
Where applicable, experiments conform with Society ethical requirements