Why are some people drawn to risky behaviors while others remain more cautious? New research with mice suggests a single gene may be key.

Scientists at the Fred Hutchinson Cancer Research Center in Seattle found that a neurodevelopmental gene called neuroD2 is related to the development of the amygdala, the brain's emotional center. They also found that this gene directs the formation of both emotional memory and the fear response.

"Most of us are familiar with the fact that we can remember things better if those memories are formed at a time when there is a strong emotional impact -- times when we are frightened, angry or falling in love. That's called emotional-memory formation. The amygdala is the part of the brain that is responsible for formation of emotional memory," research leader Dr. James Olson, associate member of Hutchinson's Clinical Research Division, said in a prepared statement.

His team studied mice with a single copy of neuroD2, and found that these mice had a reduced ability to form emotional memories and conditioned fear, compared to normal mice with two copies of the gene. The researchers also found that mice with a single copy of neuroD2 had fewer nerve cells in the amygdala than normal mice.

The study appears in this week's online issue of the Proceedings of the National Academy of Sciences.

"The contribution we have made is showing that neuroD2 is related to the development of the amygdala. This is the first time that a specific neurodevelopment gene has been related to these emotional activities in the brain," Olson said.

Further research is needed to better understand how this gene may affect human behaviors such as risk-taking and the fear response.

"The question is, are there differences in the neuroD2 gene-coding sequence or differences downstream of the neuroD2 pathway during brain development that could affect either psychiatric or emotional functions in humans? It's a completely unexplored question," Olson said. And he said it's "the immediate next question you would go to if you want to understand how this gene impacts human behavior."