Cerebral Hemodynamic Response to Unpleasant Odors in the Preterm Newborn Measured by Near-Infrared Spectroscopy

Abstract

Newborn infants in intensive care units are exposed to several unfamiliar smells, mostly related to the nosocomial environment. How the preterm baby perceives these olfactory stimulations remains unclear. Near-infrared spectroscopy can be performed noninvasively above the olfactory cortex to monitor changes of cerebral blood flow as an indicator of cortical activation. The aim of this study was to explore by near-infrared spectroscopy how odorous substances routinely used in the neonatal intensive care unit influence bilateral cortical hemodynamics in the olfactory region of the brains of preterm infants. Specifically, a detergent (Neomidil) and an adhesive remover (Remove) have been tested. Twenty preterm neonates of gestational age 30 -37 wk (mean 33.7 Ϯ 2.3 SD) and postconceptional age 32-37.3 wk (mean 35.5 Ϯ 2.75 SD) were monitored by near-infrared spectroscopy. Two optode pairs were placed above the anterior orbitofrontal gyri, which is involved in olfactory processing, on each side of the skull. Fifteen babies were exposed to the smell of a disinfectant and five babies to that of a detergent, both applied to small cotton pads. Changes of oxygenated Hb and deoxygenated Hb were recorded before, during, and after a 10-s stimulus. In 17 out of 20 babies, there was a decrease in oxygenated Hb and total Hb after the exposure to the substances. The decrease was significantly greater in the right side than in the left side. This change was different from that observed in our previous study after exposure to colostrum and the pleasant smell of vanilla, which elicited an increase in blood oxygenation in the same region. The biologic significance of this finding is unknown. We conclude that cortical hemodynamic modifications occur in the preterm newborn after exposure to preparations commonly used in the neonatal intensive care unit. A lateralization seems to occur in processing unpleasant olfactory cues. The newborn infant is exposed to a multitude of nonphysiologic environmental stimuli, which are perceived, processed, and elaborated in the form of different responses, both physiologic and behavioral. Some of these stimuli have been shown to affect the growth, development, and survival of the neonate, especially the premature infant treated in the NICU (1-5). Most studies have focused on responses to visual (3, 5, 6), auditory (3,5,7,8), and tactile stimulation (1, 3, 5). However, there is little information about the responses to a large variety of pungent and artificial odorous compounds (i.e. disinfectants, detergents, adhesive removers) to which the premature baby is exposed. In a recent study by our group, we found that unfamiliar, but likely pleasant, olfactory cues such as colostrum and vanilla can elicit a hemodynamic cortical response in healthy newborns. This suggests olfactory processing (9).The olfactory system is well structured from 32-34 wk of gestation and distinct behavioral responses to olfactory stimuli

The Emergence of Human Consciousness: From Fetal to Neonatal Life

“…Near infrared spectroscopy recordings in the left anterior orbitofrontal gyri of newborns (from 6 to 192 h) in a quiet awake state show increased hemodynamic response during exposure to smells like that of colostrum or of vanilla compared with water (43). Conversely, a decreased response, which was significantly greater in the right than in the left side, was noticed when the babies were exposed to the smell of a disinfectant or of a detergent (44).…”

Assessing infants' cortical response to speech using near-infrared spectroscopy

“…Evidence that there is a relationship between hemodynamics and neural activity (Gratton et al, 2001), and that NIRS produces results consistent with other imaging techniques (fMRI and PET) used simultaneously (Kleinschmidt et al, 1996;Strangman et al, 2002b;, provides converging evidence that NIRS can provide a reliable estimate of brain activity. Occasionally, researchers find an increase, rather than a decrease, in HbR (Bartocci et al, 2001;Chen et al, 2002;Hoshi and Tamura, 1993;Jasdzewski et al, 2003;Kato et al, 1993;Sakatani et al,1999; in targeted cortical areas. Although it is not entirely clear why an increase in HbR is sometimes observed, in infants it is assumed to be a less mature hemodynamic response.…”

Near infrared spectroscopy to study the brain: an overview

“…There are few reports in the literature on hemodynamic effects in neonates, visual cortex [66][67][68], auditory cortex [69][70][71][72], speech frontal cortex [73], olfactory stimulation [74,75], pain [76][77][78], and motor cortex [14]. Bartocci's [75] findings during the presentation of unpleasant smells to infants are highly particular, because a decrease in O 2 Hb concentration was observed, while the HHb concentration remained approximately constant.…”