What your mother did when she was a child may have an effect on your memory

Feb 3 2009

A new study by researchers from Rush University Medical Center and Tufts University School of Medicine using mice indicate that a child's memory and the severity of learning disorders may be affected by what his or her mother did when she was a child.

Findings from the study will be published in the February 4th issue of The Journal of Neuroscience .

Neuroscience researchers studied the brain function of pre-adolescent mice that have a genetically-created defect in memory. When these young mice were given an enriched environment, which is exposure to stimulatory objects, enhanced social interaction and voluntary exercise for two weeks, the memory defect, caused by inhibiting the formation of Ras-GRF1 and Ras-GRF2 proteins, was reversed.

After a few months, the same mice were fertilized and they gave birth to offspring that had the same genetic mutation. However, the offspring had no indications of the memory defect even though the offspring were never exposed to an enriched environment like their mothers.

Previous research in mouse models has shown that early exposure to an enriched environment while pregnant can also positively affect offspring.

"What is so unique about this study is that we provided an enriched environment during pre-adolescence, months before the mice became pregnant, yet the beneficial effect reached into the next generation," said Dean Hartley, PhD, neuroscience researcher at Rush University Medical Center and study co-investigator. "The offspring had improved memory even without an enriched environment."

"We were able to demonstrate that environmental enrichment during youth has dramatic additional powers," said Hartley. "It can enhance the memory in future offspring of enriched juvenile mice."

To prove that that improved memory of the offspring was not the result of better nurturing by mothers who were enriched when they were young, a number of offspring were raised by non-enriched foster mothers. Even in the offspring raised by non-enriched mothers, they still maintained an improved memory.

"This example of 'inheritance of acquired characters' was first proposed by Jean- Baptiste Lamarck in the early 1800s. However, it is incompatible with classical Mendelian genetics, which states that we inherit qualities from our parents through specific DNA sequences they inherited from their parents. We now refer to this type of inheritance as epigenetics, which involves environmentally-induced changes in the structure of DNA and the chromosomes in which DNA resides that are passed on to offspring," said Larry Feig, PhD, professor of biochemistry at Tufts University School of Medicine.

Previous research has shown that a relatively brief exposure to an enriched environment in both normal and memory-deficient mice unlocks an otherwise latent biochemical control mechanism that enhances a cellular process in nerve cells called long-term potentiation (LTP). LTP is thought to be involved in learning and memory. This enhancement was detected in pre-adolescent mice but not in adult mice, reflecting the brain's higher plasticity in the young.

"This is the first study to demonstrate an inheritance of a change in a signaling pathway that promotes LTP and enhancement of memory formation, and that defects caused by a genetic mutation can be reversed by what the mother is exposed to during her youth," said Hartley.

The phenomenon described in this study indicates that juvenile enrichment affects LTP in the next generation. However, the study found that it does not in subsequent generations because the effect of the enriched environment wears off faster in the offspring.