From times immemorial, it has been noticed that a woman wants to gobble up a baby placed in her arms, even if the baby is not hers.

Reward circuit
For their experiment, the researchers presented two groups of 15 women with the odours of others' newborns while the women were subjected to brain imaging tests. The first group was composed of women who had given birth 3-6 weeks prior to the experiment, and the other group consisted of women who had never given birth. All the women were non-smokers. The odours of the newborns were collected from their pyjamas two days after birth.
Although the women in both groups perceived the odour of newborns with the same intensity, brain imaging showed greater activation in the dopaminergic system of the caudate nucleus of mothers compared to the women who had never given birth. Located in the centre of the brain, the caudate nucleus is a double structure straddling the thalamus in both hemispheres. "This structure plays a role in reward learning," explains Frasnelli. "And dopamine is the primary neurotransmitter in the neural reward circuit."
This system reinforces the motivation to act in a certain way because of the pleasure associated with a given behaviour. "This circuit makes us desire certain foods and causes addiction to tobacco and other drugs," says the researcher. "Not all odours trigger this reaction. Only those associated with reward, such as food or satisfying a desire, cause this activation."
Dopamine is also associated with sexual pleasure and other forms of gratification. Laboratory rats whose dopamine levels are stimulated by electrodes become so addicted that they stop eating.
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Questions remain
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It is also not known whether this reaction is specific to mothers, since men were not part of the experiment. "What we know now and what is new is that there is a neural response linked to the status of biological mother," he says.
Source-Eurekalert