Robert Soussignan

Bottle-fed neonates prefer an odor experienced in utero to an odor experienced postnatally in the feeding context

The head-orientation response of 2- and 4-day-old bottle-feeding neonates was studied in paired-choice odor tests. Three tests were conducted at Days 2 and 4 after birth to assess the development of the relative response between two salient odors from the prenatal and postnatal environments: (a) amniotic fluid (AF) versus formula milk (FM), (b) FM versus control stimulus (distilled water), and (c) AF versus control stimulus. At both ages, AF and FM elicited positive orientation when presented simultaneously with the control stimulus, indicating that both odors were detectable and attractive to the infants. However, when AF and FM were presented concurrently, the infants expressed significantly longer orientation response toward AF odor than toward FM odor at the age of 2 and 4 days. Within the first 4 days of life, bottle-feeders thus display olfactory preference for a prenatal substrate over a postnatal substrate to which they were recurrently exposed in the feeding situation.

Orientation responses to biological odours in the human newborn. Initial pattern and postnatal plasticity

The initial pattern and development of odour preference was studied in infants simultaneously exposed to amniotic fluid (AF) and maternal lacteal secretion (L). Five groups of varying age (range: 1-5 days) and breast-feeding experience (range: 0-32 feeds) were studied. Before postnatal day 3, no evidence of differentiation of AF and L was apparent. After 3 days and 7-12 breast-feeding episodes, a significant preference for L arised. The initial stage (days 1-3) may reflect fetal acquisition of AF odour and sensory/motivational equivalence of AF and L odours. The second stage (days 4-5) may reflect the infants perception of change in milk quality and increasing experience with milk. This sequential development attests to a high plasticity in the initial stage of human olfactory development.