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.