Babies can learn what to fear from the first days of life simply by smelling their distressed mothers, a new study has shown. This doesn't only work after the pregnancy, but also during it and even before - if a mother experiences something specific which makes her fearful.
It's the first direct observation of this kind - University of Michigan and New York University researchers studied mother rats who had learned to fear the smell of peppermint - theyalso showed that the mothers passed this fear on to their offspring and also pinpointed the exact area of the brain where the learning of fear takes places in the first days of life.
This may help explain something which has puzzled biologists for decades - how is it that a mother's traumatic experiences are passed on to her offspring?
"During the early days of an infant rat's life, they are immune to learning information about environmental dangers. But if their mother is the source of threat information, we have shown they can learn from her and produce lasting memories," says Jacek Debiec, M.D., Ph.D., the U-M psychiatrist and neuroscientist who led the research.
So in a way, even before they can actually accumulate knowledge of their own, they get a taste (or rather, a smell) of their mothers' experience.
"Our research demonstrates that infants can learn from maternal expression of fear, very early in life," he adds. "Before they can even make their own experiences, they basically acquire their mothers' experiences. Most importantly, these maternally-transmitted memories are long-lived, whereas other types of infant learning, if not repeated, rapidly perish."
In order to figure this out, they devised an experiment which involved making mother rats fear the smell of peppermint by exposing them to non harmful, but unpleasant electric shocks while they smelled the scent, before they were pregnant. Then after they gave birth, the team exposed the mothers to just the minty smell, but didn't deliver the shocks. They found that newborns quickly picked up on the fear - even though they had no direct reason to fear it. They could learn their mothers' fears even when the mothers weren't present.
Using special brain imaging, and studies of genetic activity in individual brain cells and cortisol in the blood, they found that this learning takes place in the lateral amygdala. The amygdala is present in virtually all evolved mammals, playing a complex role in the in the processing of memory, decision-making, and emotional reactions.
Researchers now hope to conduct the same kind of study for mothers and their babies, but they have every reason to believe they will get similar results.