In humans, as in many animal species - whether birds, crocodiles or mammals - the fetus is able to perceive external stimuli, and in particular sounds, at least at the end of its development. The perceived sounds can be natural (like the mother's voice), or artificial (music). And the fetus can differentiate between those that are familiar and unfamiliar to it. This prenatal sensory experience is naturally memorized. So much so that from birth, the young man recognizes his mother's voice, and he may even show a preference for music that she listened to at the end of her pregnancy.
IThere is therefore “transnatal” transmission, that is to say from the fetal stage to the postnatal stage. And this is true for different sensory modalities. An example ? Very young rats whose mothers were placed in zero gravity during gestation will exhibit disturbed balance. In fact, the behavior and physiology of their mothers are a major source ofsensory experiences for the fetus: if she feels emotions while performing a task, then changes in heart rate are observed in her.
How well can he memorize associations?
Capable oflearning by association - by memorizing the link between a stimulus and its feeling - the fetus is therefore sensitive to the emotions felt by its mother. But until now, no study has made it possible to bring these two processes together. To what extent can the fetus associate perceived stimuli at the same time as the emotions felt by its mother, and then memorize this association? This is precisely the question we asked ourselves in the laboratories Physiology, Environment and Genetics for Animals and Livestock Systems) and Animal and Human Ethology.
To answer, we chose a animal model : the pig. With the idea of testing whether the sounds broadcast to the mother during gestation, while giving her more or less positive experiences on an emotional level, could then have an impact on the reactions of the little ones when listening to these same ones. sounds. Having a very developed hearing and recognized cognitive capacities, while being the object of breeding and being easily manipulated, the pig was the ideal model. We therefore read texts broadcast over loudspeakers, while associating them with positive or negative emotional experiences in pregnant sows. Then we observed the reaction of the piglets to these same texts, just after their birth and in the following weeks.
In total, during the last month of gestation, 38 sows were subjected daily to 10 minutes of petting or other sources of positive emotions in the morning, then 10 minutes of sudden gestures or other sources of negative emotions afterwards. midday. Three groups were formed. In two "test" groups, composed of 10 sows each, these treatments were associated with a particular human voice (voice A for the positive treatment and voice B for the negative treatment for group 1, voice B for the positive and voice A for the negative for group 2). Finally, in a “control” group, also comprising 10 sows, these same treatments were applied without voices being broadcast. The sows heard no other voices, as the keepers were instructed never to speak to them.
After birth, three observations
After birth, the piglets were subjected to five-minute social separation tests, then being placed alone in a room. Such a situation usually leads them to utter "cries of distress" which indicate their level of stress. However, we were able to make three observations.
First, whether they were two days or three weeks old, piglets who heard human voices before birth were less stressed than control piglets when these same voices were played to them during the test: these voices were therefore perceived as "familiar". , after having been memorized in utero.
Second, when a new voice reading the same text was played, it also had a calming effect, proof that the piglets had generalized the effect of a voice to any human voice.
Third, finally, the piglets were more stressed by a voice associated by their mother with a negative emotion than linked to a positive emotion. They had therefore memorized the association between their mother's voice and their feelings, and this memory had a major impact on their reactions.
Ultimately, these results are the first demonstration of in utero learning by association between a sensory stimulus and the emotional state of the mother. And they should have major fallout. First, because they highlight the potential impact of the voice of caregivers on pregnant mothers of domestic or captive species. Secondly, because they can be extended to humans. We could use it to soothe newborns in difficult circumstances - for example, in the event of premature birth - by making them listen to certain music. And we should probably reconsider the usual recommendations around pregnancy.
Alban Lemasson, Professor at the University of Rennes 1, director of the animal and human ethology laboratory (EthoS), Rennes 1 University et Martine Hausberger, Research director at CNRS. Leads the PEGASE research team within the animal and human ethology laboratory (EthoS), Rennes 1 University
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