Human Foetuses Learn Odours from their Pregnant Motherís Diet

Benoist Schaal, Luc Marlier and Robert Soussignan

Olfactory responsiveness was assessed in 24 neonates born to mothers who had or had not consumed anise flavour during pregnancy. Both groups of infants were followed-up for behavioural markers of attraction and aversion when exposed to anise odour and a control odour immediately after birth and on day 4. Infants born to anise-consuming mothers evinced a stable preference for anise odour over this period, whereas those born to anise non-consuming mothers displayed aversion or neutral responses. This study provides the first clear evidence that through their diet human mothers influence the hedonic polarity of their neonatesí initial olfactory responses. The findings have potential implications for the early mother-to-infant transmission of chemosensory information relative to food and addictive products.

During the embryonic or foetal stages, the environment constrains the perceptual information available to the growing brain and thus influences the behaviour of the newborn (Smotherman and Robinson, 1988; Lecanuet et al., 1995; Gottlieb, 1997). In humans, for example, the way vocal and speech sounds are processed by the newborn depends on prenatal exposure to maternal voice or specific speech sequences (De Casper and Spence, 1986; Fifer and Moon, 1995). Whether this foetal ability is indicative of mechanisms specific to audition and language processing or of more general learning mechanisms applicable to a broad range of perceptual inputs remains unclear. We investigated whether the human foetus can acquire information from olfactory cues, which are involved in other psychobiological realms such as ingestive behaviour, emotional stability and early attachment (Schaal, 1988).

The ability to learn olfactory cues has been demonstrated in the foetuses of various mammals, such as rats (Pedersen and Blass, 1982; Smotherman, 1982; Smotherman and Robinson, 1987; Hepper, 1988; Molina et al., 1995), rabbits (Bilků et al., 1994; Semke et al., 1995) and sheep (Schaal et al., 1995a). In these species, the introduction of odorants into the amnion either by direct infusion or maternal ingestion affects later infantile responses to the same stimuli. These studies in non-primate species highlight the fact that chemosensory information is part of the normal experience of the foetus. It is the aim of the present study to examine whether similar prenatal facilitative or inductive processes [in the sense of Gottlieb (Gottlieb, 1983)] might operate in the formation of the earliest selective responses to odours in human infants.

Taking advantage of the widespread use of anise flavour in the local Alsatian cuisine and of the fact that it is readily perceived by newborns immediately after birth (Stirnimann, 1936; Engen and Lipsitt, 1965), we studied odour-elicited responses in infants born to mothers who had regularly consumed anise flavoured sweets or drinks during late pregnancy and infants born to mothers who had not ingested such products during pregnancy.

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