Personality Differences in Genetically Identical Twins Explained

Personality isn't just nature--it's also nurture. Now, researchers have discovered a bit more about how different personalities develop even among identical twins. The findings could allow researchers to better understand how exactly the brain forms during a person's lifetime.

In order to examine why people develop such different personalities, the researchers examined 40 genetically identical mice that were kept in an enclosure that offered a large variety of activity and exploration options. The mice themselves were equipped with special micro-chips that emitted electromagnetic signals. These chips allowed the scientists to construct the mice's movement profiles and to quantify their exploratory behavior.

"The animals were not only genetically identical, they were also living in the same environment," said principal investigator Gerd Kempermann in a news release. "However, this environment was so rich that each mouse gathered its own individual experiences in it."

It's these individual experiences that help define a mouse's (and possibly a person's) personality. The researchers discovered highly individualized behavioral patterns, and the differences only increased over time.

"These differences were associated with differences in the generation of new neurons in the hippocampus, a region of the brain that supports learning and memory," said Kempermann. "Animals that explored the environment to a greater degree also grew more new neurons than animals that were more passive."

In fact, this study is the first of its kind to show that personal experiences and ensuing behavior contribute to individualization of the brain. The generation of new neurons in the hippocampus allows the brain to react to new information flexibly. This individualization actually cannot be reduced to differences in environment or genetic makeup.

The study could allow researchers to better understand how personal experiences influence behavior and the development of personality. It has important implications for psychology, education science and medicine.

"Our findings show that development itself contributes to differences in adult behavior," said Ulman Lindenberger, one of the researchers, in a new release. "This is what many have assumed, but now there is direct neurobiological evidence in support of this claim. Our results suggest that experience influences the aging of the human mind."

The findings are published in the journal Science.