Mothers involuntarily teach their babies what to fear, through a sense of commons

Babies can quickly learn what to fear, and what not to fear, through a sense of odour, which is emitted from their mother, says a group of researchers from the United States.

This depends completely on their mother's past experiences. These experiences could have happened to the mother many years before the birth of the baby, but the fear still remains. Hence, when the mother experiences such a feeling, near the baby, she unknowingly emits a smell, which the baby picks up, and in the process, learns when to be afraid.

"Our research demonstrates that infants can learn from maternal expressions of fear, very early in life," said Jacek Debiec, MD, PhD, a U-M Neuroscientist and Psychiatrist who was also the leader of the research, in a press release. "Before they can make their own experiences, they basically acquire their mother's experiences. Most importantly, these maternally transmitted memories are long-lived, whereas other types of infant learning, if not repeated, rapidly perish."

The study, which was published in Proceedings of the National Academy of Sciences, was conducted by a team of researchers from the New York University and the University of Michigan Medical School.

The researchers used their lab rats in the experiments to delve into the psyche of mother-child relationship. The mother rats were given mild electric shocks, while they were exposed to the smell of peppermint. In other words, the smell of peppermint triggered some traumatic experience in the mother's memory. These mother rats were trained to fear the smell of the peppermint long before they were even pregnant.

As a control, they also kept another group of mother rats who were not given electric shocks while being exposed to the smell of peppermint. The smell of peppermint did not trigger any traumatic memories for them.

However the scientists found that after these traumatised rats had babies, the baby rats too quickly learnt to fear the smell of peppermint. These mothers "taught" their babies to fear the smell of peppermint. 

The researchers also found the process, through which the mothers taught the babies the fear of the peppermint. They found that the mother rat releases an alarm odour, when they smelt peppermint. The baby rats quickly picked up this odour, and learnt to fear the smell of peppermint, themselves.

Meanwhile, the babies of the rats who were not traumatised were not taught to fear the smell of peppermint.

"During the early days of an infant rat's life, they are immune to learning information about environmental dangers," said Debiec. "But their mother is the source of threat information, we have shown they can learn from her and produce lasting memories."

Debiec, who is from Poland, says that he has been told by many of his patients (who were children of holocaust victims) that they had nightmares, in which they saw flashes of the holocaust, although they had never seen the holocaust themselves.

He believes that a similar phenomenon exists in humans too, and that human babies can quickly learn such responses from their mothers as well. Although he says that there is a long way to go in this research for them to find a treatment for such patients, he believes that this research has helped them take a giant stride forward in understanding what works behind fear, in the human mind.