It’s no surprise that the phobias and fears of parents may be passed on to children. Parents are, after all, role models for their kids, good or bad. But, according to recent research, phobias developed during our lifetimes may be passed on to our children even before child rearing begins—at the moment of conception.
This parental legacy was the focus of a study at the Yerkes National Primate Research Center at Emory University. Scientists at the center conditioned lab mice to avoid the smell of cherry blossoms by giving the mice a mild electric shock when they were exposed to the flower’s aroma. A learned aversion was confirmed by verifying that the mice were startled by the aroma later when there was no accompanying shock. Then it was the researchers’ turn to be startled. They discovered that the offspring of the conditioned mice also had an aversion to the blossom smell, and were also better able to detect this scent compared to non-conditioned mice.
Inheritance of the phobia at the gene level was confirmed by a number of striking findings. Baby mice from conditioned parents who were then raised from birth by a foster mother with no phobia had the cherry blossom phobia as adults. The phobic behavior also occurred in mice conceived by in vitro fertilization that were then raised by a foster mother. And baby mice from non-conditioned parents did not develop the phobia when they were raised by a conditioned mother.
But the most fascinating finding may be what happened one generation later. The grandchildren of the conditioned mice also had the aversion, even if they were raised from birth by neutral mice with no phobia history.
Examinations of the phobic offspring revealed that more space in the smell-processing part of their brains was devoted to the cherry blossom odor. This change may have been due to activation of nose cells and of the odor receptor gene in brain cells. These alterations appear to be an example of “epigenesis”—a change in a gene based on the effects of chemicals or factors other than a change in the genetic code itself. (For more on epigenesis, see Cellular Time Machine Heralds New Era in Healing
Epigenesis shows that our genes respond to stressors from the environment. By changing gene activity, these stressors can then affect both how we perceive stimuli in the environment and how we respond to them. Repeated exposure to aversive stimuli can thereby make the aversion permanent, hard-wiring it into our brains. Once the change becomes part of our genetic makeup, it can be passed down to the next generation.
This inheritance of acquired traits has been borne out by a number of studies of people traumatized by war, famine, and other adverse circumstances. Emotional and psychological fallout from such trauma has been seen in the children of these victims, even in offspring born well after the traumatizing event. There’s a plus side to this type of heritability, however. Avoidance of what can hurt us has genuine survival value. Parents who learn to fear dangerous situations can pass on this aversion genetically, giving their children valuable predispositions for survival right from the start.
Epigenetics is helping to lead the way to a better understanding of the actual basis of phobias and other behaviors, which could then open up a pathway to new treatment breakthroughs. “Knowing how the experiences of parents influence their descendants helps us to understand psychiatric disorders that may have a trans-generational basis, and possibly to design therapeutic strategies,” notes Kerry Ressler, M.D., Ph.D., professor of psychiatry and behavioral sciences at Emory School of Medicine, who was one of the investigators in the mice study.
The million-dollar question: Can a genetic alteration resulting in undesirable behavior be reversed? It will take a lot more than studies of flower-avoiding mice to answer that one.