For any anime fans out there, when I read the phrase "inherit memory", I immediately thought of Tanjiro from Demon Slayer when he had some sort of vision or dream where he saw somebody that looked exactly like him, but had his own family and spoke with this samurai-looking guy with a similar scar on his forehead just like Tanjiro had. Later on, it was mentioned how some people get inherited memories from their ancestors, and so Tanjiro concluded that the person in the dream was actually one of his ancestors.
Fiction aside, some researchers have conducted an experiment that purports how certain "memories" or "experiences" may be passed down to next generations. And the answer, according to them, lies in genetics. Furthermore, it's more than just memories or experiences, they suggest that even traits such as temperament, longevity, resilience to mental ill-health, and even ideological leanings can be embedded in the genetic framework of an individual and inherited by their descendants.
Originally, one of the earlier experiments on epigenetics was conducted by a team from Emory University in Georgia, led by Prof. Kerry Ressler, in which they used mice to study the effects of lived experience and acquired knowledge, and how those are transmitted from one generation of mice to the next.
First, they stimulated the mice by exposing them to the scent of cherries, immediately followed by a mild electric shock. After associating the smell of cherries with the pain from the shock, the mice had internalized a certain fear or anxiety about cherries. Next, the researchers bred the mice once. and then those pups were bred again.
When the researchers exposed the grandpups to the smell of cherries, it was quite surprising to discover that the grandpups had the same reaction to the cherries as their grandparents did. From this, the team identified a particular gene that had been changed. Instead of the nerve cells directing the stimulus of the cherries to the pleasure and reward circuits, it was rerouted to the amygdala, the part of the brain that registered fear.
In order to ensure that these results were not affected by other factors such as learning by imitation, the researchers bred the original mice again and raised the new pups away from their parents. Some of the grandpups were also fostered out. Both these groups still reacted the same way to the cherries as the traumatized mice. Furthermore, the researchers also bred mice who had no such traumatic experience and had the pups fostered by the traumatized mice, and the pups were unaffected.
This leads to the conclusion that certain traumatic events may change the way neurons are wired to react to certain stimuli and that can be passed on to the next generations through DNA. But the whole study doesn't end there. The researchers also tried to reverse the effect of the traumatic linking. And they found that after some repetitions, the traumatized mice's neural circuits had reverted to their original wiring. After breeding them again, the researchers found that the trauma wasn't passed on to subsequent generations.
With this study as the background, another team of researchers led by Prof. Rachel Yehuda at the Icahn School of Medicine at Mount Sinai Medical School in New York in 2020, tried to examine whether the same neural circuitry can be found in humans by looking into the genetics of Holocaust survivors and their children, and they saw that, for people who have gone through trauma, there were particular changes to the gene linked to levels of cortisol.
In 2021, Prof. Yehuda looked at genes linked to the immune system, and they found that the changes caused by the traumatic event had affected the way the immune system interacted with the central nervous system. The disruptions caused by the immune system had been linked to depression, anxiety, psychosis, and autism.
Although we won't necessarily have the same kind of experience that Tanjiro had in the show, wherein he saw vividly the experience of his ancestor as if looking through their eyes, there are certain things that our ancestors may have passed on to us if they had gone through traumatic or life-altering experiences. Those changes may have been embedded into the genes and affect later generations, causing them to be more susceptible to diseases or mental health concerns.
(Image credit: Johnny Cohen/Unsplash)